Ethylene oxide catalyst and process for preparing the catalyst

• US 4,766,105 A
• Filed: 10/31/1986
• Issued: 08/23/1988
• Est. Priority Date: 10/31/1986
• Status: Expired due to Term

• Current Assignee: Shell Oil Company (Shell Plc)
• Original Assignee: Shell Oil Company (Shell Plc)
• Inventors: Lauritzen, Ann M.
• Primary Examiner(s): SHINE, WILLIAM
• Application Number:
  US06/926,025
• Time in Patent Office: 662 Days
• Field of Search: 502/216, 502/317, 502/347, 502/348, 549/536
• US Class Current: 502/216
• CPC Class Codes: B01J 23/688 with manganese, technetium or rhenium
• CPC Class Codes: C07D 301/10 with catalysts containing silver or gold
• CPC Class Codes: Y02P 20/52 using catalysts, e.g. selective catalysts

Abstract

This invention relates to an ethylene oxide catalyst having an improved selectivity which catalyst comprises silver, a promoting amount of alkali metal, a promoting amount of rhenium and a promoting amount of rhenium co-promotor selected from sulfur, molbydenum, tungsten, chromium and mixtures thereof supported on a porous refractory support.

Claims

1. An ethylene oxide catalyst for the vapor phase production of ethylene oxide from ethylene and oxygen comprising a catalytically effective amount of silver, a promoting amount of alkali metal and a promoting amount of rhenium and a promoting amount of rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof supported on a suitable support having a surface area ranging from about 0.05 to about 10 m² /g.

6. The catalyst of claims 1, 2, 3, 4 or 5 wherein the rhenium co-promoter comprises an oxidic compound.

7. The catalyst of claim 6 wherein the support comprises alpha alumina.

8. The catalyst of claim 7 wherein the support surface area ranges from about 0.05 to about 5 m² /g.

9. The catalyst of claim 8 wherein the support surface area ranges from about 0.1 to about 3 m² /g.

10. The catalyst of claim 9 wherein the silver ranges from about 1 to about 25 percent by weight of the total catalyst, and the alkali metal promoter ranges from about 20 to about 1500 parts by weight, measured as the metal, per million parts by weight of the total catalyst.

11. The catalyst of claim 10 wherein the silver ranges from about 5 to about 20 percent by weight of the total catalyst and the alkali metal promoter ranges from about 50 to about 1000 parts by weight, measured as the metal, per million parts by weight of the total catalyst.

12. The catalyst of claim 11 wherein the alkali metal, rhenium and rhenium co-promoter are found on the surface of the support or on the surface of the catalyst.

13. The catalyst of claim 11 wherein the alkali metal, rhenium and rhenium co-promoter are found individually or in any mixture thereof on the catalyst, on the support or on both the catalyst and the support.

14. The catalyst of claim 11 wherein the selectivity is measured at an oxygen conversion level of about 40% at a gas hourly space velocity of about 3300 and when the catalyst has been placed on stream for about 16±

4 hours.

19. The catalyst of claim 1 wherein said promoting amount of alkali metal, rhenium and rhenium co-promoter in combination with the silver and support is such as to provide a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from alkali metal, rhenium and rhenium co-promoter.

20. The catalyst of claim 19 wherein the selectivity is measured at an oxygen conversion level of about 40% at a gas hourly space velocity of about 3300 and when the catalyst has been placed onstream for about 16±

4 hours.

21. The catalyst of claim 1 wherein the silver ranges from about 1 to about 25 percent by weight of the total catalyst, the alkali metal promoter ranges from about 20 to about 1500 parts by weight, measured as the metal, per million parts by weight of total catalyst, the rhenium ranges from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst and the rhenium co-promoter ranges from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst.

2. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising silver, alkali metal promoter, from about 0.2 to about 5 millimoles of rhenium promoter, measured as the metal, per kilogram of total catalyst, and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of a rhenium co-promoter comprising sulfur, molybdenum, tungsten, chromium or mixtures thereof supported on a porous, refractory support;

the combination of silver, alkali metal promoter, rhenium promoter, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from alkali metal, rhenium and rhenium co-promoter.

3. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising silver, alkali metal promoter, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof, supported on a porous, refractory support wherein the rhenium is applied to the support in the form of a perrhenate or rhenium heptoxide and the rhenium co-promoter is applied to the support in the form of an oxidic compound or an oxyanion;

the combination of silver, alkali metal promoter, rhenium, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from alkali metal, rhenium and rhenium co-promoter.

15. The catalyst of claims 3 or 5 wherein the rhenium co-promoter which is applied to the support is selected from sulfate, sulfite, sulfonate, molybdate, tungstate, chromate and mixtures thereof.

16. The catalyst of claim 15 wherein the support comprises alpha alumina, the silver ranges from about 1 to about 25 percent by weight of the total catalyst and the alkali metal promoter ranges from about 20 to about 1500 ppm by weight of the total catalyst.

17. The catalyst of claim 16 wherein the silver ranges from about 5 to about 20 percent by weight and the alkali metal promoter ranges from about 50 to about 1000 ppm by weight.

18. The catalyst of claim 17 wherein the selectivity is measured at an oxygen conversion level of about 40% at a gas hourly space velocity of about 3300 and when the catalyst has been placed on stream for about 16±

4 hours.

4. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising silver, alkali metal promoter, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst in a form which is extractable in a dilute (20 millimolar) aqueous solution of sodium hydroxide, and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof supported on a porous, refractory support;

the combination of silver, alkali metal promoter, rhenium and rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from alkali metal, rhenium and rhenium co-promoter.

5. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising silver, alkali metal promoter, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst in a form which is extractable in a dilute (20 millimolar) aqueous solution of sodium hydroxide and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof supported on a porous, refractory support wherein the rhenium is applied to the support in the form of a perrhenate or rhenium heptooxide and the rhenium co-promoter is applied to the support in the form of an oxidic compound or an oxyanion;

the combination of silver, alkali metal promoter, rhenium, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from alkali metal, rhenium and rhenium co-promoter.

22. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising silver, alkali metal promoter, from about 0.2 to about 5 millimoles of rhenium promoter, measured as the metal, per kilogram of total catalyst, and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of a rhenium co-promoter comprising sulfur, molybdenum, tungsten, chromium or mixtures thereof supported on a porous, refractory support having a surface area ranging from about 0.05 to about 10 m² /g;

the combination of silver, alkali metal promoter, rhenium promoter, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from alkali metal, rhenium and rhenium co-promoter.

23. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising silver, alkali metal promoter, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof, supported on a porous, refractory support having a surface area ranging from about 0.05 to about 10 m² /g wherein the rhenium is applied to the support in the form of a perrhenate or rhenium heptoxide and the rhenium co-promoter is applied to the support in the form of an oxidic compound or an oxyanion;

the combination of silver, alkali metal promoter, rhenium, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from alkali metal, rhenium and rhenium co-promoter.

24. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising silver, alkali metal promoter, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst in a form which is extractable in a dilute (20 millimolar) aqueous solution of sodium hydroxide, and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof supported on a porous, refractory support having a surface area ranging from about 0.05 to about 10 m² /g;

the combination of silver, alkali metal promoter, rhenium and rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from alkali metal, rhenium and rhenium co-promoter.

25. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising silver, alkali metal promoter, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst in a form which is extractable in a dilute (20 millimolar) aqueous solution of sodium hydroxide and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof supported on a porous, refractory support having a surface area ranging from about 0.05 to about 10 m² /g wherein the rhenium is applied to the support in the form of a perrhenate or rhenium heptoxide and the rhenium co-promoter is applied to the support in the form of an oxidic compound or an oxyanion;

the combination of silver, alkali metal promoter, rhenium, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from alkali metal, rhenium and rhenium co-promoter.

26. An ethylene oxide catalyst for the vapor phase production of ethylene oxide from ethylene and oxygen comprising a catalytically effective amount of silver, a promoting amount of a higher alkali metal comprising potassium, rubidium, cesium, or mixtures thereof, a promoting amount of rhenium and a promoting amount of a rhenium co-promoter comprising sulfur, molybdenum, tungsten, chromium or mixtures thereof, supported on a suitable support having a surface area ranging from about 0.05 to about 10 m² /g.

40. The catalyst of any of claims 26-35 wherein the rhenium co-promoter comprises an oxidic compound.

41. The catalyst of claim 40 wherein the support comprises alpha alumina.

42. The catalyst of claim 41 wherein the support comprises alpha alumina which has a surface area ranging from about 0.05 to about 5 m² /g and a water pore volume ranging from about 0.10 to about 0.75 cc/g.

43. The catalyst of claim 42 wherein the support surface area ranges from about 0.1 to about 3 m² /g.

44. The catalyst of claims 26 or 27 wherein the silver ranges from about 1 to about 25 percent by weight of the total catalyst, the higher alkali metal promoter ranges from about 20 to about 1500 parts by weight, measured as the metal, per million parts by weight of total catalyst, the rhenium ranges from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst, the rhenium co-promoter ranges from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst and the support comprises alpha alumina with a surface area ranging from about 0.05 to about 5 m² /g.

45. The catalyst of claim 44 wherein said promoting amount of higher alkali metal, rhenium and rhenium co-promoter in combination with the silver and support is such as to provide a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from higher alkali metal, rhenium and rhenium co-promoter.

46. The catalyst of claim 45 wherein the selectivity is measured at an oxygen conversion level of about 40% at a gas hourly space velocity of about 3300 and when the catalyst has been placed onstream for about 16±

4 hours.

47. The catalyst of claim 44 wherein the higher alkali metal ranges from about 50 to about 1000 ppm by weight.

48. The catalyst of claim 47 wherein the higher alkali metal comprises potassium.

49. The catalyst of claim 47 wherein the higher alkali metal comprises rubidium.

50. The catalyst of claim 47 wherein the higher alkali metal comprises cesium.

51. The catalyst of claim 47 wherein the higher alkali metal comprises potassium and cesium.

52. The catalyst of claim 47 wherein the higher alkali metal comprises rubidium and cesium.

53. The catalyst of claim 47 wherein the higher alkali metal comprises cesium, rubidium and potassium.

54. The catalyst of claim 47 wherein the alkali metal, rhenium and rhenium co-promoter are found on the surface of the support.

55. The catalyst of claim 47 wherein the alkali metal, rhenium and rhenium co-promoter are found on the surface of the catalyst.

56. The catalyst of claim 47 wherein the alkali metal, rhenium and rhenium co-promoter are found individually or in any mixture thereof on the catalyst, on the support or on both the catalyst and the support.

27. An ethylene oxide catalyst for the vapor phase production of ethylene oxide from ethylene and oxygen comprising a catalytically effective amount of silver, a promoting amount of a higher alkali metal selected from the group consisting of potassium, rubidium, cesium and mixtures thereof, a promoting amount of rhenium and a promoting amount of a rhenium co-promoter selected from the group consisting of sulfur, molybdenum, tungsten, chromium and mixtures thereof, supported on a porous, refractory support having a surface area ranging from about 0.05 to about 10 m² /g.

28. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising silver, a higher alkali metal promoter comprising potassium, rubidium, cesium or mixtures thereof, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst and from about 0.2 to about 5 millimoles, measured as the element per kilogram of total catalyst, of a rhenium co-promoter comprising sulfur, molybdenum, tungsten, chromium or mixtures thereof supported on a porous, refractory support;

the combination of silver, higher alkali metal promoter, rhenium promoter, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from higher alkali metal, rhenium and rhenium co-promoter.

57. The catalyst of claims 28, 29, 30 or 31 wherein the silver ranges from about 1 to about 25 percent by weight of the total catalyst and the alkali metal promoter ranges from about 20 to about 1500 parts by weight, measured as the metal, per million parts by weight of the total catalyst.

58. The catalyst of claim 57 wherein the silver ranges from about 5 to about 20 percent by weight of the total catalyst and the alkali metal promoter ranges from about 50 to about 1000 parts by weight, measured as the metal, per million parts by weight of the total catalyst.

59. The catalyst of claim 58 wherein the alkali metal comprises potassium.

60. The catalyst of claim 58 wherein the alkali metal comprises rubidium.

61. The catalyst of claim 58 wherein the alkali metal comprises cesium.

62. The catalyst of claim 58 wherein the alkali metal, rhenium and rhenium co-promoter are found on the surface of the catalyst.

63. The catalyst of claim 58 wherein the alkali metal, rhenium and rhenium co-promoter are found on the surface of the support.

64. The catalyst of claim 58 wherein the alkali metal, rhenium and rhenium co-promoter are found individually or in any mixture thereof on the catalyst, on the support or on both the catalyst and the support.

65. The catalyst of claim 58 wherein the selectivity is measured at an oxygen conversion level of about 40% at a gas hourly space velocity of about 3300 and when the catalyst has been placed onstream for about 16±

4 hours.

29. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising silver, a higher alkali metal promoter comprising potassium, rubidium, cesium or mixtures thereof, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof supported on a porous, refractory support wherein the rhenium is applied to the support in the form of a perrhenate or rhenium heptoxide and the rhenium co-promoter is applied to the support in the form of an oxidic compound or an oxyanion;

the combination of silver, higher alkali metal promoter, rhenium, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from higher alkali metal, rhenium and rhenium co-promoter.

69. The catalyst of claims 29, 31, 33 or 35 wherein the rhenium co-promoter which is applied to the support is selected from sulfate, sulfite, sulfonate, molybdate, tungstate, chromate and mixtures thereof.

30. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising silver, a higher alkali metal promoter comprising potassium, rubidium, cesium or mixtures thereof, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst in a form which is extractable in a dilute (20 millimolar) aqueous solution of sodium hydroxide, and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof supported on a porous, refractory support;

the combination of silver, higher alkali metal promoter, rhenium, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from higher alkali metal, rhenium and rhenium co-promoter.

31. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising silver, a higher alkali metal promoter comprising potassium, rubidium, cesium or mixtures thereof, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst in a form which is extractable in a dilute (20 millimolar) aqueous solution of sodium hydroxide and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof, supported on a porous, refractory support wherein the rhenium is applied to the support in the form of a perrhenate or rhenium heptoxide and the rhenium co-promoter is applied to the support in the form of an oxidic compound or an oxyanion;

the combination of silver, higher alkali metal promoter, rhenium, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from higher alkali metal, rhenium and rhenium co-promoter.

32. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising from about 1 to about 25 percent by weight of total catalyst of silver, from about 50 to about 1000 parts by weight, measured as the metal, per million parts by weight of total catalyst of a higher alkali metal promoter selected from potassium, rubidium, cesium and mixtures thereof, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof supported on a porous, refractory support comprising alpha alumina having a surface area ranging from about 0.1 to about 3 m² /g and a water pore volume ranging from about 0.25 to about 0.55 cc/gm;

the combination of silver, higher alkali metal, rhenium, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from higher alkali metal, rhenium and rhenium co-promoter.

66. The catalyst of claims 32, 33, 34 or 35 wherein the silver ranges from about 5 to about 20 percent by weight.

67. The catalyst of claims 32, 33, 34 or 35 wherein the alkali metal, rhenium and rhenium co-promoter are found on the surface of the support or on the surface of the catalyst.

68. The catalyst of claims 32, 33, 34 or 35 wherein the alkali metal, rhenium and rhenium co-promoter are found individually or in any mixture thereof on the catalyst, on the support or on both the catalyst and the support.

70. The catalyst of claim 66 wherein the higher alkali metal comprises potassium.

71. The catalyst of claim 66 wherein the higher alkali metal comprises rubidium.

72. The catalyst of claim 66 wherein the higher alkali metal comprises cesium.

33. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising from about 1 to about 25 percent by weight of total catalyst of silver, from about 50 to about 1000 parts by weight, measured as the metal, per million parts by weight of total catalyst of a higher alkali metal promoter selected from potassium, rubidium, cesium and mixtures thereof, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof supported on a porous, refractory support comprising alpha alumina having a surface area ranging from about 0.1 to about 3 m² /g and a water pore volume ranging from about 0.25 to about 0.55 cc/gm wherein the rhenium is applied to the support in the form of a perrhenate or rhenium heptoxide and the rhenium co-promoter is applied to the support in the form of an oxidic compound or an oxyanion;

the combination of silver, higher alkali metal, rhenium, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from higher alkali metal, rhenium and rhenium co-promoter.

34. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising from about 1 to about 25 percent by weight of total catalyst of silver, from about 50 to about 1000 parts by weight, measured as the metal, per million parts by weight of total catalyst of a higher alkali metal promoter selected from potassium, rubidium, cesium and mixtures thereof, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst in a form which is extractable in a dilute (20 millimolar) aqueous solution of sodium hydroxide and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof supported on a porous, refractory support comprising alpha alumina having a surface area ranging from about 0.1 to about 3 m² /g and a water pore volume ranging from about 0.25 to about 0.55 cc/gm;

the combination of silver, higher alkali metal, rhenium, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from higher alkali metal, rhenium and rhenium co-promoter.

35. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising from about 1 to about 25 percent by weight of total catalyst of silver, from about 50 to about 1000 parts by weight, measured as the metal, per million parts by weight of total catalyst of a higher alkali metal promoter selected from potassium, rubidium, cesium and mixtures thereof, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst in a form which is extractable in a dilute (20 millimolar) aqueous solution of sodium hydroxide and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of a rhenium co-promoter selected from sulfur, molbydenum, tungsten, chromium and mixtures thereof supported on a porous, refractory support comprising alpha alumina having a surface area ranging from about 0.1 to about 3 m² /g and a water pore volume ranging from about 0.25 to about 0.55 cc/gm wherein the rhenium is applied to the support in the form of a perrhenate or rhenium heptoxide and the rhenium co-promoter is applied to the support in the form of an oxidic compound or an oxyanion;

the combination of silver, higher alkali metal, rhenium, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from higher alkali metal, rhenium and rhenium co-promoter.

36. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising silver, a higher alkali metal promoter comprising potassium, rubidium, cesium or mixtures thereof, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst and from about 0.2 to about 5 millimoles, measured as the element per kilogram of total catalyst, of a rhenium co-promoter comprising sulfur, molybdenum, tungsten, chromium or mixtures thereof supported on a porous, refractory support having a surface area ranging from about 0.05 to about 10 m² /g;

the combination of silver, higher alkali metal promoter, rhenium promoter, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from higher alkali metal, rhenium and rhenium co-promoter.

37. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising silver, a higher alkali metal promoter comprising potassium, rubidium, cesium or mixtures thereof, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof supported on a porous, refractory support having a surface area ranging from about 0.05 to about 10 m² /g wherein the rhenium is applied to the support in the form of a perrhenate or rhenium heptoxide and the rhenium co-promoter is applied to the support in the form of an oxidic compound or an oxyanion;

the combination of silver, higher alkali metal promoter, rhenium, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from higher alkali metal, rhenium and rhenium co-promoter.

38. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising silver, a higher alkali metal promoter comprising potassium, rubidium, cesium or mixtures thereof, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst in a form which is extractable in a dilute (20 millimolar) aqueous solution of sodium hydroxide, and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof supported on a porous, refractory support having a surface area ranging from about 0.05 to about 10 m² /g;

the combination of silver, higher alkali metal promoter, rhenium, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from higher alkali metal, rhenium and rhenium co-promoter.

39. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising silver, a higher alkali metal promoter comprising potassium, rubidium, cesium or mixtures thereof, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst in a form which is extractable in a dilute (20 millimolar) aqueous solution of sodium hydroxide and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof, supported on a porous, refractory support having a surface area ranging from about 0.05 to about 10 m² /g wherein the rhenium is applied to the support in the form of a perrhenate or rhenium heptoxide and the rhenium co-promoter is applied to the support in the form of an oxidic compound or an oxyanion;

the combination of silver, higher alkali metal promoter, rhenium, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from higher alkali metal, rhenium and rhenium co-promoter.

73. An ethylene oxide catalyst for the vapor phase production of ethylene oxide from ethylene and oxygen comprising a catalytically effective amount of silver, a promoting amount of cesium, a promoting amount of rhenium and a promoting amount of rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof on a porous refractory support comprising alpha alumina having a surface area ranging from about 0.05 to about 10 m² /g.

78. The catalyst of claim 73 wherein the silver ranges from about 1 to about 25 percent by weight of the total catalyst, the cesium ranges from about 20 to about 1500 parts by weight, measured as the metal, per million parts by weight of the total catalyst, the rhenium ranges from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst and the rhenium co-promoter ranges from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst.

79. The catalyst of claim 78 wherein the cesium ranges from about 50 to about 1000 ppm by weight of the total catalyst.

80. The catalyst of claim 79 wherein the support has a surface area ranging from about 0.05 to about 5 m² /g.

81. The catalyst of claim 80 wherein the support surface area ranges from about 0.1 to about 3 m² /g.

82. The catalyst of claim 73 wherein said promoting amount of cesium, rhenium and rhenium co-promoter in combination with the silver and support is such as to provide a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from alkali metal, rhenium and rhenium co-promoter.

85. The catalyst of claims 73, 74, 75, 76 or 77 wherein the cesium, rhenium and rhenium co-promoter are found on the surface of the support or on the surface of the catalyst.

86. The catalyst of claims 73, 74, 75, 76 or 77 wherein the cesium, rhenium and rhenium co-promoter are found individually or in any mixture thereof on the catalyst, on the support, or on both the catalyst and the support.

74. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising from about 1 to about 25 percent by weight of total catalyst of silver, from about 50 to about 1000 parts by weight, measured as the metal, per million parts by weight of total catalyst of cesium promoter, from about 0.2 to about 5 millimoles of rhenium promoter, measured as the metal, per kilogram of total catalyst and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof supported on a porous, refractory support comprising alpha alumina having a surface area ranging from about 0.1 to about 3 m² /g and a water pore volume ranging from about 0.25 to about 0.55 cc/gm;

the combination of silver, cesium promoter, rhenium promoter, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from cesium, rhenium and rhenium co-promoter.

83. The catalyst of claims 74, 75, 76, 77 or 82 wherein the selectivity is measured at an oxygen conversion level of about 40% at a gas hourly space velocity of about 3300 and when the catalyst has been placed onstream for about 16±

4 hours.

75. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising from about 1 to about 25 percent by weight of total catalyst of silver, from about 50 to about 1000 parts by weight, measured as the metal, per million parts by weight of total catalyst of cesium promoter, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof supported on a porous refractory support comprising alpha alumina having a surface area ranging from about 0.1 to about 3 m² /g and a water pore volume ranging from about 0.25 to about 0.55 cc/g wherein the rhenium is applied to the support as ammonium or alkali metal perrhenate or rhenium heptoxide or mixtures thereof and the rhenium co-promoter is applied to the support in the form of an oxidic compound or an oxyanion;

the combination of silver, cesium promoter, rhenium, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from cesium, rhenium and rhenium co-promoter.

84. The catalyst of claim 75 wherein the rhenium co-promoter which is applied to the support is selected from sulfate, sulfite, sulfonate, molybdate, tungstate, chromate and mixtures thereof.

76. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising from about 1 to about 25 percent by weight of total catalyst of silver, from about 50 to about 1000 parts by weight, measured as the metal, per million parts by weight of total catalyst of cesium promoter, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst in a form which is extractable in a dilute (20 millimolar) aqueous solution of sodium hydroxide and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof supported on a porous, refractory support comprising alpha alumina having a surface area ranging from about 0.1 to about 3 m² /g and a water pore volume ranging from about 0.25 to about 0.55 cc/gm;

the combination of silver, cesium, rhenium, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from cesium, rhenium and rhenium co-promoter.

77. A catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen comprising from about 1 to about 25 percent by weight of total catalyst of silver, from about 50 to about 1000 parts by weight, measured as the metal, per million parts by weight of total catalyst of cesium promoter, from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst in a form which is extractable in a dilute (20 millimolar) aqueous solution of sodium hydroxide and from about 0.2 to about 5 millimoles measured as the element, per kilogram of total catalyst, of a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof supported on a porous refractory support comprising alpha alumina having a surface area ranging from about 0.1 to about 3 m² /g and a water pore volume ranging from about 0.25 to about 0.55 cc/g wherein the rhenium is applied to the support as ammonium or alkali metal perrhenate or rhenium heptoxide or mixtures thereof and the rhenium co-promoter is applied to the support as a sulfate, sulfite, sulfonate, molybdate, tungstate, chromate and mixtures thereof;

the combination of silver, cesium promoter, rhenium, rhenium co-promoter and support affording a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from cesium, rhenium and rhenium co-promoter.

87. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous refractory support with a catalytically effective amount of silver, a promoting amount of alkali metal, a promoting amount of rhenium and a promoting amount of a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof.

102. The process of claims 87, 88, 92, 93, 97 or 98 wherein the amount of silver added by impregnation ranges from about 1 to about 25 percent by weight, the amount of alkali metal added by impregnation ranges from about 20 to about 1500 ppm by weight, measured as the metal, the amount of rhenium added by impregnation ranges from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst and the amount of rhenium co-promoter added by impregnation ranges from about 0.2 to about 5 millimoles measured as the element, per kilogram of total catalyst.

103. The process of claims 87, 88, 92, 93, 97 or 98 wherein the amount of silver found on the surface of the support ranges from about 1 to about 25 percent by weight, the amount of alkali metal found on the catalyst ranges from about 20 to about 1500 ppm by weight, measured as the metal, the amount of rhenium found on the catalyst ranges from about 0.2 to about 5 millimoles of rhenium measured as the metal, per kilogram of total catalyst and the amount of rhenium co-promoter found on the catalyst ranges from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst.

104. The process of claims 87, 88, 92, 93, 97 or 98 wherein the amount of silver found on the surface of the support ranges from about 1 to about 25 percent by weight, the amount of alkali metal found on the surface of the support ranges from about 20 to about 1500 ppm by weight, measured as the metal, the amount of rhenium found on the surface of the support ranges from about 0.2 to about 5 millimoles of rhenium, measured as the metal, per kilogram of total catalyst and the amount of rhenium co-promoter found on the surface of the support ranges from about 0.2 to about 5 millimoles, measured as the element, per kilograms of total catalyst.

105. The process of claims 87, 88, 89, 92, 93, 94, 97, 98 or 99 wherein after impregnation the silver is reduced to metallic silver.

88. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and oxygen which comprises impregnating a porous refractory support with one or more solutions comprising silver, alkali metal, rhenium and/or a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof wherein the concentration of the silver (measured as the metal) in the solution ranges from about 1 g/l to the solubility limit of silver in the solution, the concentration of alkali metal (measured as the metal) in the solution ranges from about 1×

10^-3 g/l to about 12 g/l, the concentration of the rhenium (measured as the metal) ranges from about 5×

10^-3 g/l to about 20 g/l and the concentration of rhenium co-promoter (measured as the element) ranges from about 1×

10^-3 g/l to about 20 g/l to provide the catalyst with a catalytically effective amount of silver, a promoting amount of alkali metal, a promoting amount of rhenium, and a promoting amount of rhenium co-promoter.

89. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous refractory support with one or more solutions comprising solvent having silver compound(s) dissolved therein, and/or alkali metal compound(s) dissolved therein and/or rhenium-containing compound(s) dissolved therein and/or rhenium co-promoter compound(s) selected from compound(s) of sulfur, molybdenum, tungsten, chromium and mixtures thereof dissolved therein sufficient to deposit on the support from about 1 to about 25 percent by weight of total catalyst of silver compound(s), measured as the metal, from about 20 to about 1500 ppm by weight of alkali metal compound(s), measured as the metal, from about 0.2 to about 5 millimoles per kilogram of total catalyst, measured as the metal, of rhenium-containing compound(s) and from about 0.2 to about 5 millimoles per kilogram of total catalyst, measured as the element, of rhenium co-promoter compound(s) to provide the catalyst with a catalytically effective amount of silver, a promoting amount of alkali metal, a promoting amount of rhenium and a promoting amount of rhenium co-promoter.

112. The process of claims 89, 94 or 99 wherein the silver compound is selected from silver oxalate, silver oxide, silver carbonate, silver lactate and mixtures thereof.

113. The process of claims 89, 94 or 99 wherein the alkali metal compound is a hydroxide and/or a nitrate.

114. The process of claims 89, 94 or 99 wherein the rhenium-containing compound is ammonium and/or alkali metal perrhenate and/or rhenium heptoxide.

115. The process of claims 89, 94 or 99 wherein the sulfur compound is ammonium or alkali metal sulfate, sulfite or sulfonate or sulfuric, sulfurous or sulfonic acid, the tungsten compound is ammonium or alkali metal tungstate or tungstic acid, the molybdenum compound is ammonium or alkali metal molybdate or molybdic acid and the chromium compound is ammonium or alkali metal chromate or dichromate or chromic or dichromic acid.

116. The process of claims 89, 94 or 99 wherein the alkali metal compound is cesium hydroxide or cesium nitrate, the rhenium compound is ammonium or alkali metal perrhenate or rhenium heptoxide, the sulfur compound is ammonium or alkali metal sulfate, sulfite or sulfonate or sulfuric, sulfurous or sulfonic acid, the tungsten compound is ammonium or alkali metal tungstate or tungstic acid, the molybdenum compound is ammonium or alkali metal molybdate or molybdic acid and the chromium compound is ammonium or alkali metal chromate or dichromate or chromic or dichromic acid.

117. The process of claims 89, 94 or 99 wherein the silver compound is selected from silver oxalate, silver oxide, silver carbonate, silver lactate and mixtures thereof, the alkali metal compound is cesium hydroxide or cesium nitrate, the rhenium compound is ammonium or alkali metal perrhenate or rhenium heptoxide, the sulfur compound is ammonium or alkali metal sulfate, sulfite or sulfonate or sulfuric, sulfurous or sulfonic acid, the tungsten compound is ammonium or alkali metal tungstate or tungstic acid, the molybdenum compound is ammonium or alkali metal molybdate or molybdic acid and the chromium compound is ammonium or alkali metal chromate or dichromate or chromic or dichromic acid.

90. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous, refractory support with one or more solutions comprising silver ions, alkali metal ions, rhenium-containing ions, rhenium co-promoter ions selected from ions containing sulfur, molybdenum, tungsten, chromium and mixtures thereof or mixtures of any of the aforementioned ions thereof sufficient to deposit on the carrier from about 1 to about 25 percent by weight of total catalyst of silver, from about 20 to about 1500 parts by weight, measured as the metal, per million parts by weight of total catalyst, of alkali metal compound(s), from about 0.2 to about 5 millimoles of rhenium-containing compound(s), measured as the metal, per kilogram of total catalyst, and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst of rhenium co-promoter compound(s) selected from compound(s) of sulfur, molybdenum, tungsten, chromium and mixtures thereof;

and after impregnation, reducing the silver on the support to metallic silver to cause the combination of silver, alkali metal promoter, rhenium, rhenium co-promotor and support to have a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from alkali metal, rhenium and rhenium co-promoter.

91. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous, refractory support with one or more solutions comprising silver ions, alkali metal ions, rhenium-containing ions, rhenium co-promoter ions containing sulfur, molybdenum, tungsten, chromium and mixtures thereof or mixtures of any of the aforementioned ions thereof sufficient to deposit on the support from about 1 to about 25 percent by weight of total catalyst of silver, from about 20 to about 1500 parts by weight, measured as the metal, per million parts by weight of total catalyst, of alkali metal compound(s), from about 0.2 to about 5 millimoles of rhenium compound(s), measured as the metal, per kilogram of total catalyst, said rhenium compound(s) providing in the final catalyst rhenium in a form which is extractable in a dilute (20 millimolar) aqueous sodium hydroxide solution and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of rhenium co-promoter compound(s) selected from compound(s) containing sulfur, molybdenum, tungsten, chromium and mixtures thereof;

and after impregnation, reducing the silver on the support to metallic silver to cause the combination of silver, alkali metal promoter, rhenium, rhenium co-promoter and support to have a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from alkali metal, rhenium and rhenium co-promoter.

92. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous refractory support comprising alpha alumina with a catalytically effective amount of silver, a promoting amount of higher alkali metal comprising potassium, rubidium, cesium or mixtures thereof, a promoting amount of rhenium and a promoting amount of rhenium co-promoter comprising sulfur, molybdenum, tungsten, chromium and mixtures thereof.

93. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous refractory support comprising alpha alumina with one or more solutions comprising silver, higher alkali metal selected from the group consisting of potassium, rubidium, cesium and mixtures thereof, rhenium and/or rhenium co-promoter selected from the group consisting of sulfur, molybdenum, tungsten, chromium and mixtures thereof wherein the concentration of the silver (measured as the metal) in the solution ranges from about 1 g/l to the solubility limit of silver in the solution, the concentration of alkali metal (measured as the metal) in the solution ranges from about 1×

10^-3 to about 12 g/l, the concentration of the rhenium (measured as the metal) ranges from about 5×

10^-3 g/l to about 20 g/l and the concentration of rhenium co-promoter (measured as the element) ranges from about 1×

10^-3 g/l to about 20 g/l to provide the catalyst with a catalytically effective amount of silver, a promoting amount of higher alkali metal, a promoting amount of rhenium and a promoting amount of rhenium co-promoter.

94. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous refractory support comprising alpha alumina with one or more solutions comprising solvent having silver compound(s) dissolved therein, and/or higher alkali metal compound(s) selected from compound(s) of potassium, rubidium, cesium and mixtures thereof dissolved therein and/or rhenium-containing compound(s) dissolved therein and/or rhenium co-promoter compound(s) selected from compound(s) of sulfur, molybdenum, tungsten, chromium and mixtures thereof dissolved therein sufficient to deposit on the support from about 1 to about 25 percent by weight of total catalyst of silver compound(s), measured as the metal, from about 20 to about 1500 ppm by weight of higher alkali metal compound(s), measured as the metal, from about 0.2 to about 5 millimoles per kilogram of total catalyst of rhenium-containing compound(s), measured as the metal and from about 0.2 to about 5 millimoles per kilogram of total catalyst, measured as the element, of rhenium co-promoter compound(s) to provide a catalyst with a catalytically effective amount of silver, a promoting amount of higher alkali metal, a promoting amount of rhenium and a promoting amount of rhenium co-promoter.

95. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous, refractory support comprising alpha alumina with one or more solutions comprising silver ions, higher alkali metal ions selected from the group consisting of ions of potassium, rubidium, cesium and mixtures thereof, rhenium-containing ions, rhenium co-promoter ions selected from ions containing sulfur, molybdenum, tungsten, chromium and mixtures thereof or mixtures of any of the aforementioned ions thereof sufficient to deposit on the support from about 1 to about 25 percent by weight of total catalyst of silver, from about 20 to about 1500 parts by weight, measured as the metal, per million parts by weight of total catalyst, of higher alkali metal compound(s) selected from compound(s) of potassium, rubidium, cesium and mixtures thereof, from about 0.2 to about 5 millimoles of rhenium-containing compound(s), measured as the metal, per kilogram of total catalyst, and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst of rhenium co-promoter compound(s) selected from compound(s) of sulfur, molybdenum, tungsten, chromium and mixtures thereof and after impregnation, reducing the silver on the support to metallic silver to cause the combination of silver, higher alkali metal promoter, rhenium, rhenium co-promoter and support to have a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from higher alkali metal, rhenium and rhenium co-promoter.

96. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous, refractory support comprising alpha alumina with one or more solutions comprising silver ions, higher alkali metal ions selected from the group consisting of ions of potassium, rubidium, cesium and mixtures thereof, rhenium-containing ions, rhenium co-promoter ions containing sulfur, molybdenum, tungsten, chromium and mixtures thereof or mixtures of any of the aforementioned ions thereof sufficient to deposit on the support from about 1 to about 25 percent by weight of total catalyst of silver, from about 20 to about 1500 parts by weight, measured as the metal, per million parts by weight of total catalyst, of higher alkali metal compound(s) selected from compound(s) of potassium, rubidium, cesium and mixtures thereof, from about 0.2 to about 5 millimoles of rhenium-containing compound(s), measured as the metal, per kilogram of total catalyst, said rhenium-containing compound(s) providing in the final catalyst rhenium in a form which is extractable in a dilute (20 millimolar) aqueous sodium hydroxide solution and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst of rhenium co-promoter compound(s) selected from compound(s) containing sulfur, molybdenum, tungsten, chromium and mixtures thereof;

and after impregnation, reducing the silver on the support to metallic silver to cause the combination of silver, higher alkali metal, rhenium, rhenium co-promoter and support to have a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from higher alkali metal, rhenium and rhenium co-promoter.

97. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous refractory support comprising alpha alumina with a catalytically effective amount of silver, a promoting amount of cesium, a promoting amount of rhenium and a promoting amount of rhenium co-promoter comprising sulfur, molybdenum, tungsten, chromium or mixtures thereof.

98. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and oxygen which comprises impregnating a porous refractory support comprising alpha alumina with one or more solutions comprising silver, cesium, rhenium and/or rhenium co-promoter selected from the group consisting of sulfur, molybdenum, tungsten, chromium and mixtures thereof wherein the concentration of the silver (measured as the metal) in the solution ranges from about 1 g/l to the solubility limit of silver in the solution, the concentration of cesium (measured as the metal) in the solution ranges from about 1×

10^-3 g/l to about 12 g/l, the concentration of the rhenium (measured as the metal) ranges from about 5×

10^-3 g/l to about 20 g/l and the concentration of rhenium co-promoter (measured as the element) ranges from about 1×

10^-3 g/l to about 20 g/l to provide the catalyst with a catalytically effective amount of silver, a promoting amount of cesium, a promoting amount of rhenium and a promoting amount of rhenium co-promoter.

99. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which comprises impregnating a porous refractory support comprising alpha alumina with one or more solutions comprising solvent having silver compound(s) dissolved therein, cesium compound(s) dissolved therein, rhenium-containing compound(s) dissolved therein and rhenium co-promoter compound(s) selected from compound(s) of sulfur, molybdenum, tungsten, chromium and mixtures thereof dissolved therein sufficient to deposit on the support from about 1 to about 25 percent by weight of total catalyst of the silver compound(s), measured as the metal, from about 20 to about 1500 ppm by weight of cesium compound(s) measured as the metal, from about 0.2 to about 5 millimoles per kilogram of total catalyst of rhenium-containing compound(s), measured as the metal, and from about 0.2 to about 5 millimoles per kilogram of total catalyst, measured as the element, of rhenium co-promoter compound(s) to provide the catalyst with a catalytically effective amount of silver, a promoting amount of cesium, a promoting amount of rhenium and a promoting amount of rhenium co-promoter.

100. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous, refractory support comprising alpha alumina with one or more solutions comprising silver ions, cesium ions, rhenium-containing ions, rhenium co-promoter ions selected from ions containing sulfur, molybdenum, tungsten, chromium and mixtures thereof or mixtures of any of the aforementioned ions thereof sufficient to deposit on the support from about 1 to about 25 percent by weight of total catalyst of silver, from about 20 to about 1500 parts by weight, measured as the metal per million parts by weight of total catalyst, of cesium, from about 0.2 to about 5 millimoles of rhenium-containing compound(s), measured as the metal, per kilogram of total catalyst, and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst of rhenium co-promoter compound(s) selected from compound(s) of sulfur, molybdenum, tungsten, chromium and mixtures thereof and after impregnation, reducing the silver on the support to metallic silver to cause the combination of silver, cesium, rhenium, rhenium co-promoter and support to have a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from cesium, rhenium and rhenium co-promoter.

106. The process as in any of claims 87-101 wherein after impregnation the silver is reduced to metallic silver by heating at a temperature between about 75°

C. to about 400°

C.

107. The process as in any of claims 87-101 wherein after impregnation the silver is reduced to metallic silver by heating at a temperature between about 50°

C. to about 600°

C.

108. The process of claims 88, 89, 90, 91, 93, 94, 95, 96, 98, 99, 100 or 101 wherein the solution containing silver also comprises water and vicinal alkylenediamine(s) of from 2 to 4 carbon atoms.

109. The process of claims 88, 89, 90, 91, 93, 94, 95, 97, 98, 99, 100 or 101 wherein the solution containing silver also comprises water and ethylenediamine.

110. The process of claims 88, 89, 90, 91, 93, 94, 95, 97, 98, 99, 100 or 101 wherein the solution containing silver also comprises water, vicinal alkalenediamine(s) of from 2 to 4 carbon atoms and vicinal alkanolamine(s) of from 2 to 4 carbon atoms.

111. The process of claims 88, 89, 90, 91, 93, 94, 95, 96, 98, 99, 100 or 101 wherein the solution containing silver also comprises water, ethylenediamine and monoethanolamine.

118. The process of claims 90, 91, 95, 96, 100 or 101 wherein the rhenium-containing ions are perrhenate ions.

119. The process of claims 90, 91, 95, 96, 100 or 101 wherein the rhenium co-promoter ions are selected from sulfate, sulfite, sulfonate, molybdate, tungstate, chromate ions and mixtures thereof.

120. The process of claims 90, 91, 95, 96, 100 or 101 wherein the rhenium-containing ions are perrhenate ions and the rhenium co-promoter ions are selected from sulfate, sulfite, sulfonate, molybdate, tungstate, chromate ions and mixtures thereof.

121. The process of claims 90, 91, 95, 96, 100 or 101 wherein the selectivity is measured at an oxygen conversion of about 40% at a gas hourly space velocity of about 3300 and when the catalyst has been placed onstream for about 16±

4 hours.

101. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous, refractory support comprising alpha alumina with one or more solutions comprising silver ions, cesium ions, rhenium-containing ions, rhenium co-promoter ions containing sulfur, molybdenum, tungsten, chromium and mixtures thereof or mixtures of any of the aforementioned ions thereof, sufficient to deposit on the support from about 1 to about 25 percent by weight of total catalyst of silver, from about 20 to about 1500 parts by weight, measured as the metal, per million parts by weight of total catalyst, of cesium compound(s), from about 0.2 to about 5 millimoles of a rhenium-containing compound(s), measured as the metal, per kilogram of total catalyst, said rhenium-containing compound(s) providing in the final catalyst rhenium in a form which is extractable in a dilute (20 millimolar) aqueous sodium hydroxide solution and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of rhenium co-promoter compound(s) containing sulfur, molybdenum, tungsten, chromium and mixtures thereof;

and after impregnation, reducing the silver on the support to metallic silver to cause the combination of silver, cesium, rhenium, rhenium co-promoter and support to have a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from cesium, rhenium and rhenium co-promoter.

122. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous refractory support having a surface area ranging from about 0.05 to about 10 m² /g with a catalytically effective amount of silver, a promoting amount of alkali metal, a promoting amount of rhenium and a promoting amount of a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof.

123. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and oxygen which comprises impregnating a porous refractory support having a surface area ranging from about 0.05 to about 10 m² /g with one or more solutions comprising silver, alkali metal, rhenium and/or a rhenium co-promoter selected from sulfur, molybdenum, tungsten, chromium and mixtures thereof wherein the concentration of the silver (measured as the metal) in the solution ranges from about 1 g/l to the solubility limit of silver in the solution, the concentration of alkali metal (measured as the metal) in the solution ranges from about 1×

10^-3 g/l to about 12 g/l, the concentration of the rhenium (measured as the metal) ranges from about 5×

10^-3 g/l to about 20 g/l and the concentration of rhenium co-promoter (measured as the element) ranges from about 1×

10^-3 g/l to about 20 g/l to provide the catalyst with a catalytically effective amount of silver, a promoting amount of alkali metal, a promoting amount of rhenium, and a promoting amount of rhenium co-promoter.

124. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous refractory support having a surface area ranging from about 0.05 to about 10 m² /g with one or more solutions comprising solvent having silver compound(s) dissolved therein, and/or alkali metal compound(s) dissolved therein and/or rhenium-containing compound(s) dissolved therein and/or rhenium co-promoter compound(s) selected from compound(s) of sulfur, molybdenum, tungsten, chromium and mixtures thereof dissolved therein sufficient to deposit on the support from about 1 to about 25 percent by weight of total catalyst of silver compound(s), measured as the metal, from about 20 to about 1500 ppm by weight of alkali metal compound(s), measured as the metal, from about 0.2 to about 5 millimoles per kilogram of total catalyst, measured as the metal, of rhenium-containing compound(s) and from about 0.2 to about 5 millimoles per kilogram of total catalyst, measured as the element, of rhenium co-promoter compound(s) to provide the catalyst with a catalytically effective amount of silver, a promoting amount of alkali metal, a promoting amount of rhenium and a promoting amount(s) of rhenium co-promoter(s).

125. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous, refractory support having a surface area ranging from about 0.05 to about 10 m² /g with one or more solutions comprising silver ions, alkali metal ions, rhenium-containing ions, rhenium co-promoter ions selected from ions containing sulfur, molybdenum, tungsten, chromium and mixtures thereof or mixtures of any of the aforementioned ions thereof sufficient to deposit on the carrier from about 1 to about 25 percent by weight of total catalyst of silver, from about 20 to about 1500 parts by weight, measured as the metal, per million parts by weight of total catalyst, of alkali metal compound(s), from about 0.2 to about 5 millimoles of rhenium-containing compound(s), measured as the metal, per kilogram of total catalyst, and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst of rhenium co-promoter compound(s), selected from compound(s) of sulfur, molybdenum, tungsten, chromium and mixtures thereof;

and after impregnation, reducing the silver on the support to metallic silver to cause the combination of silver, alkali metal promoter, rhenium, rhenium co-promoter and support to have a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from alkali metal, rhenium and rhenium co-promoter.

126. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous, refractory support having a surface area ranging from about 0.05 to about 10 m² /g with one or more solutions comprising silver ions, alkali metal ions, rhenium-containing ions, rhenium co-promoter ions containing sulfur, molybdenum, tungsten, chromium and mixtures thereof or mixtures of any of the aforementioned ions thereof sufficient to deposit on the support from about 1 to about 25 percent by weight of total catalyst of silver, from about 20 to about 1500 parts by weight, measured as the metal, per million parts by weight of total catalyst, of alkali metal compound(s), from about 0.2 to about 5 millimoles of rhenium compound(s), measured as the metal, per kilogram of total catalyst, said rhenium compound(s) providing in the final catalyst rhenium in a form which is extractable in a dilute (20 millimolar) aqueous sodium hydroxide solution and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of rhenium co-promoter compound(s) selected from compound(s) containing sulfur, molybdenum, tungsten, chromium and mixtures thereof;

and after impregnation, reducing the silver on the support to metallic silver to cause the combination of silver, alkali metal promoter, rhenium, rhenium co-promoter and support to have a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from alkali metal, rhenium and rhenium co-promoter.

127. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous refractory support comprising alpha alumina having a surface area ranging from about 0.05 to about 10 m² /g with a catalytically effective amount of silver, a promoting amount of higher alkali metal comprising potassium, rubidium, cesium or mixtures thereof, a promoting amount of rhenium and a promoting amount of rhenium co-promoter comprising sulfur, molybdenum, tungsten, chromium and mixtures thereof.

128. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous refractory support comprising alpha alumina having a surface area ranging from about 0.05 to about 10 m² /g with one or more solutions comprising silver, higher alkali metal selected from the group consisting of potassium, rubidium, cesium and mixtures thereof, rhenium and/or rhenium co-promoter selected from the group consisting of sulfur, molybdenum, tungsten, chromium and mixtures thereof wherein the concentration of the silver (measured as the metal) in the solution ranges from about 1 g/l to the solubility limit of silver in the solution, the concentration of alkali metal (measured as the metal) in the solution ranges from about 1×

10^-3 to about 12 g/l, the concentration of the rhenium (measured as the metal) ranges from about 5×

10^-3 g/l to about 20 g/l and the concentration of rhenium co-promoter (measured as the element) ranges from about 1×

10^-3 g/l to about 20 g/l to provide the catalyst with a catalytically effective amount of silver, a promoting amount of higher alkali metal, a promoting amount of rhenium and a promoting amount of rhenium co-promoter.

129. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous refractory support comprising alpha alumina having a surface area ranging from about 0.05 to about 10 m² /g with one or more solutions comprising solvent having silver compound(s) dissolved therein, and/or higher alkali metal compound(s) selected from compound(s) of potassium, rubidium, cesium and mixtures thereof dissolved therein and/or rhenium-containing compound(s) dissolved therein and/or rhenium co-promoter compound(s) selected from compound(s) of sulfur, molybdenum, tungsten, chromium and mixtures thereof dissolved therein sufficient to deposit on the support from about 1 to about 25 percent by weight of total catalyst of silver compound(s), measured as the metal, from about 20 to about 1500 ppm by weight of higher alkali metal compound(s), measured as the metal, from about 0.2 to about 5 millimoles per kilogram of total catalyst of rhenium-containing compound(s), measured as the metal and from about 0.2 to about 5 millimoles per kilogram of total catalyst, measured as the element, of rhenium co-promoter compound(s) to provide a catalyst with a catalytically effective amount of silver, a promoting amount of higher alkali metal, a promoting amount of rhenium and a promoting amount of rhenium co-promoter.

130. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous, refractory support comprising alpha alumina having a surface area ranging from about 0.05 to about 10 m² /g with one or more solutions comprising silver ions, higher alkali metal ions selected from the group consisting of ions of potassium, rubidium, cesium and mixtures thereof, rhenium-containing ions, rhenium co-promoter ions selected from ions containing sulfur, molybdenum, tungsten, chromium and mixtures thereof or mixtures of any of the aforementioned ions thereof sufficient to deposit on the support from about 1 to about 25 percent by weight of total catalyst of silver, from about 20 to about 1500 parts by weight, measured as the metal, per million parts by weight of total catalyst, of higher alkali metal compound(s) selected from compound(s) of potassium, rubidium, cesium and mixtures thereof, from about 0.2 to about 5 millimoles of rhenium-containing compound(s), measured as the metal, per kilogram of total catalyst, and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst of rhenium co-promoter compound(s) selected from compound(s) of sulfur, molybdenum, tungsten, chromium and mixtures thereof and after impregnation, reducing the silver on the support to metallic silver to cause the combination of silver, higher alkali metal promoter, rhenium, rhenium co-promoter and support to have a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from higher alkali metal, rhenium and rhenium co-promoter.

131. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous, refractory support comprising alpha alumina having a surface area ranging from about 0.05 to about 10 m² /g with one or more solutions comprising silver ions, higher alkali metal ions selected from the group consisting of ions of potassium, rubidium, cesium and mixtures thereof, rhenium-containing ions, rhenium co-promoter ions containing sulfur, molybdenum, tungsten, chromium and mixtures thereof or mixtures of any of the aforementioned ions thereof sufficient to deposit on the support from about 1 to about 25 percent by weight of total catalyst of silver, from about 20 to about 1500 parts by weight, measured as the metal, per million parts by weight of total catalyst, of higher alkali metal compound(s) selected from compound(s) of potassium, rubidium, cesium and mixtures thereof, from about 0.2 to about 5 millimoles of rhenium-containing compound(s), measured as the metal, per kilogram of total catalyst, said rhenium-containing compound(s) providing in the final catalyst rhenium in a form which is extractable in a dilute (20 millimolar) aqueous sodium hydroxide solution and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst of rhenium co-promoter compound(s) selected from compound(s) containing sulfur, molybdenum, tungsten, chromium and mixtures thereof;

and after impregnation, reducing the silver on the support to metallic silver to cause the combination of silver, higher alkali metal, rhenium, rhenium co-promoter and support to have a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from higher alkali metal, rhenium and rhenium co-promoter.

132. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous refractory support comprising alpha alumina having a surface are ranging from about 0.05 to about 10 m² /g with a catalytically effective amount of silver, a promoting amount of cesium, a promoting amount of rhenium and a promoting amount of rhenium co-promoter comprising sulfur, molybdenum, tungsten, chromium or mixtures thereof.

133. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and oxygen which comprises impregnating a porous refractory support comprising alpha alumina having a surface area ranging from about 0.05 to about 10 m² /g with one or more solutions comprising silver, cesium, rhenium and/or rhenium co-promoter selected from the group consisting of sulfur, molybdenum, tungsten, chromium and mixtures thereof wherein the concentration of the silver (measured as the metal) in the solution ranges from about 1 g/l to the solubility limit of silver in the solution, the concentration of cesium (measured as the metal) in the solution ranges from about 1×

10^-3 g/l to about 12 g/l, the concentration of the rhenium (measured as the metal) ranges from about 5×

10^-3 g/l to about 20 g/l and the concentration of rhenium co-promoter (measured as the element) ranges from about 1×

10^-3 g/l to about 20 g/l to provide the catalyst with a catalytically effective amount of silver, a promoting amount of cesium, a promoting amount of rhenium and a promoting amount of rhenium co-promoter.

134. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which comprises impregnating a porous refractory support comprising alpha alumina having a surface area ranging from about 0.05 to about 10 m² /g with one or more solutions comprising solvent having silver compound(s) dissolved therein, cesium compound(s) dissolved therein, rhenium-containing compound(s) dissolved therein and rhenium co-promoter compound(s) selected from compound(s) of sulfur, molybdenum, tungsten, chromium and mixtures thereof dissolved therein sufficient to deposit on the support from about 1 to about 25 percent by weight of total catalyst of the silver compound(s), measured as the metal, from about 20 to about 1500 ppm by weight of cesium compound(s) measured as the metal, from about 0.2 to about 5 millimoles per kilogram of total catalyst of rhenium-containing compound(s), measured as the metal, and from about 0.2 to about 5 millimoles per kilogram of total catalyst, measured as the element, a rhenium co-promoter compound(s) to provide the catalyst with a catalytically effective amount of silver, a promoting amount of cesium, a promoting amount of rhenium and a promoting amount of rhenium co-promoter.

135. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous, refractory support comprising alpha alumina having a surface area ranging from about 0.05 to about 10 m² /g with one or more solutions comprising silver ions, cesium ions, rhenium-containing ions, rhenium co-promoter ions selected from ions containing sulfur, molybdenum, tungsten, chromium and mixtures thereof or mixtures of any of the aforementioned ions thereof sufficient to deposit on the support from about 1 to about 25 percent by weight of total catalyst of silver, from about 20 to about 1500 parts by weight, measured as the metal per million parts by weight of total catalyst, of cesium, from about 0.2 to about 5 millimoles of rhenium-containing compound(s), measured as the metal, per kilogram of total catalyst, and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst of rhenium co-promoter compound(s) selected from compound(s) of sulfur, molybdenum, tungsten, chromium and mixtures thereof and after impregnation, reducing the silver on the support to metallic silver to cause the combination of silver, cesium, rhenium, rhenium co-promoter and support to have a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from cesium, rhenium and rhenium co-promoter.

136. A process for preparing a catalyst for the vapor phase production of ethylene oxide from ethylene and molecular oxygen which process comprises impregnating a porous, refractory support comprising alpha alumina having a surface area ranging from about 0.05 to about 10 m² /g with one or more solutions comprising silver ions, cesium ions, rhenium-containing ions, rhenium co-promoter ions containing sulfur, molybdenum, tungsten, chromium and mixtures thereof or mixtures of any of the aforementioned ions thereof, sufficient to deposit on the support from about 1 to about 25 percent by weight of total catalyst of silver, from about 20 to about 1500 parts by weight, measured as the metal, per million parts by weight of total catalyst, of cesium compound(s), from about 0.2 to about 5 millimoles of a rhenium-containing compound(s), measured as the metal, per kilogram of total catalyst, said rhenium-containing compound(s) providing in the final catalyst rhenium in a form which is extractable in a dilute (20 millimolar) aqueous sodium hydroxide solution and from about 0.2 to about 5 millimoles, measured as the element, per kilogram of total catalyst, of rhenium co-promoter compound(s) containing sulfur, molybdenum, tungsten, chromium and mixtures thereof;

and after impregnation, reducing the silver on the support to metallic silver to cause the combination of silver, cesium, rhenium, rhenium co-promoter and support to have a higher selectivity to ethylene oxide at a given oxygen conversion level than is obtained under the same reaction conditions with the same combination of silver and support and none, one or two of the promoters selected from cesium, rhenium and rhenium co-promoter.