Exhaust gas cleaning apparatus and method for internal combustion engine
First Claim
1. An exhaust gas purifying apparatus for an internal combustion engine, having a SOx absorbent and a NOx purifying catalyst each arranged in an exhaust path of the internal combustion engine in which lean burn is effected, said SOx absorbent absorbing SOx in an inflow exhaust gas under an oxidizing atmosphere in which the O2 concentration of said exhaust gas is higher than a stoichiometric ratio required for completely burning a reductive component contained in said exhaust gas, and releasing the absorbed SOx under a reducing atmosphere in which the Os concentration of an exhaust gas is lower than a stoichiometric ratio required for completely burning a reductive component contained in said exhaust gas, said NOx purifying catalyst capturing NOx in said exhaust gas under the oxidizing atmosphere in which the O2 concentration of said exhaust gas is higher than a stoichiometric ratio required for completely burning a purifying component contained in said exhaust gas,wherein as said NOx purifying catalyst, there is provided a NOx chemisorption reduction catalyst chemically capturing NOx as NO2 on a surface of said NOx purifying catalyst under said oxidizing atmosphere and reducing the chemically captured NO2 with said reductive component to N2 to release the N2 from the surface of said NOx purifying catalyst under said reducing atmosphere.
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Abstract
An apparatus and method of highly efficiently purifying nitrogen oxides are provided. An NOx chemisorption reduction catalyst chemically absorbs NOx under a condition that an exhaust gas of an internal combustion engine is an oxidizing atmosphere and deoxidizes adsorbed NOx under a reducing atmosphere. An SOx absorbent absorbs SOx contained in the exhaust gas of the oxidizing atmosphere, and deoxidizes and release SOx absorbed in the reducing atmospheric exhaust gas. The catalyst and absorbent are arranged in the exhaust path to purify the exhaust gas while preventing or suppressing SOx-poisoning of the NOx chemisorption reduction catalyst.
56 Citations
24 Claims
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1. An exhaust gas purifying apparatus for an internal combustion engine, having a SOx absorbent and a NOx purifying catalyst each arranged in an exhaust path of the internal combustion engine in which lean burn is effected, said SOx absorbent absorbing SOx in an inflow exhaust gas under an oxidizing atmosphere in which the O2 concentration of said exhaust gas is higher than a stoichiometric ratio required for completely burning a reductive component contained in said exhaust gas, and releasing the absorbed SOx under a reducing atmosphere in which the Os concentration of an exhaust gas is lower than a stoichiometric ratio required for completely burning a reductive component contained in said exhaust gas, said NOx purifying catalyst capturing NOx in said exhaust gas under the oxidizing atmosphere in which the O2 concentration of said exhaust gas is higher than a stoichiometric ratio required for completely burning a purifying component contained in said exhaust gas,
wherein as said NOx purifying catalyst, there is provided a NOx chemisorption reduction catalyst chemically capturing NOx as NO2 on a surface of said NOx purifying catalyst under said oxidizing atmosphere and reducing the chemically captured NO2 with said reductive component to N2 to release the N2 from the surface of said NOx purifying catalyst under said reducing atmosphere.
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17. An exhaust gas purifying apparatus for an internal combustion engine, having a SOx absorbent and a NOx reduction catalyst each arranged in an exhaust path of the internal combustion engine in which lean burn is effected, said SOx absorbent absorbing SOx in an inflow exhaust gas under an oxidizing atmosphere in which the O2 concentration of said exhaust gas is higher than a stoichiometric ratio required for completely burning a reductive component contained in said exhaust gas, and releasing the absorbed SOx under a reducing atmosphere in which the O2 concentration of an exhaust gas is lower than a stoichiometric ratio required for completely burning a reductive component contained in said exhaust gas, said NOx purification catalyst capturing NOx in said exhaust gas under the oxidizing atmosphere in which the O2 concentration of said exhaust gas is higher than a stoichiometric ratio required for completely burning a reductive component contained in said exhaust gas,
wherein as said NOx purifying catalyst, there is provided a NOx chemisorption reduction catalyst chemically capturing NOx as NO2 on a surface of said NOx purifying catalyst under said oxidizing atmosphere and reducing the chemically captured NO2 with said reductive component to N2 to release the N2 from the surface of said NOx purifying catalyst under said reducing atmosphere, an operational condition determining means for determining an operational condition of said internal combustion engine, and an air fuel ratio controlling means, and wherein said NOx chemisorption reduction catalyst includes a porous support of inorganic oxide, an oxide of a NOx chemisorption component, an oxide of a rare-earth metal and a noble metal, and said NOx chemisorption component comprises at least one kind of element selected from a group consisting of lithium, sodium, potassium, strontium, magnesium and calcium, and titanium.
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18. An exhaust gas purifying method of purifying NOx contained in an exhaust gas, by arranging, in an exhaust path of an internal combustion engine, in which lean burn is effected, a SOx absorbent absorbing SOx in an inflow exhaust gas under an oxidizing atmosphere in which the O2 concentration of said exhaust gas is higher than a stoichiometric ratio required for completely burning a reductive component contained in said exhaust gas, and releasing the absorbed SOx under a reducing atmosphere in which the O2 concentration of an exhaust gas is lower than a stoichiometric ratio required for completely burning a reductive component contained in said exhaust gas, and a NOx purification catalyst capturing NOx in said exhaust gas under the oxidizing atmosphere in which the O2 concentration of said exhaust gas is higher than a stoichiometric ratio required for completely burning a reductive component contained in said exhaust gas,
wherein said NOx purification catalyst, is formed of a NOx chemisorption reduction catalyst chemically capturing NOx as NO2 on a surface of said NOx purifying catalyst under said oxidizing atmosphere and reducing the chemically captured NO2 with said reductive component to the N2 from the surface of said NOx purifying catalyst under said reducing atmosphere, and the NOx chemically captured on a surface of said NOx chemisorption reduction catalyst when an exhaust gas flowed in said NOx chemisorption reduction catalyst is under said oxidizing atmosphere, is reduced and released as N2 by controlling an air fuel ratio so that the exhaust gas flowed in said NOx chemisorption reduction catalyst becomes a reducing atmosphere, and wherein said NOx chemisorption reduction catalyst includes a porous suppport of inorganic oxide, an oxide of a NOx chemisorption component, an oxide of a rare-earth metal and a noble metal, and said NOx chemisorption component comprises at last one kind of element selected from a group consisting of lithium, sodium, potassium, strontium and calcium, and titanium.
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21. A method of recovering a NOx chemisorption reduction catalyst, arranged in an exhaust path of an internal combustion engine and detracted from the NOx purifying ability by adsorption or absorption of SOx in an exhaust gas, wherein when a running distance or time reaches a predetermined condition, an operation is switched to a fuel rich combustion operation or stoichiometric combustion operation to release SOx from said NOx chemisorption reduction catalyst even if the operation is in a fuel lean combustion operation.
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22. A method of recovering a NOx chemisorption reduction catalyst, arranged in an exhaust path of an internal combustion engine and detracted from the NOx purifying ability by adsorption or absorption of SOx in an exhaust gas, wherein
said method comprises the steps of estimating an amount of sulfur oxides discharged to the exhaust gas from a sulfur concentration contained in a fuel and a consumed amount of the fuel; -
estimating an amount of said sulfur oxides absorbed into said catalyst, a produced amount of sulfurous salts and a converted amount from the sulfurous salts to sulfuric salts from an exhaust gas temperature and/or a catalyst temperature; and
allowing a rich gas or a stoichiometric gas to flow through said passage to reduce and decompose the sulfurous salts by forming a reductive atmosphere when an amount of the sulfurous salts or the sulfuric salts existing in the catalyst estimated from the cumulative values reaches a predetermined value.
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23. A method of recovering a NOx chemisorption reduction catalyst, arranged in an exhaust path of an internal combustion engine and detracted from the NOx purifying ability by adsorption or absorption of SOx in an exhaust gas, wherein
said method comprises the steps of estimating an amount of sulfur oxides discharged to the exhaust gas from a sulfur concentration contained in a fuel and a consumed amount of the fuel; -
estimating an amount of said sulfur oxides absorbed into said catalyst, a produced amount of sulfurous salts and a converted amount from the sulfurous salts to sulfuric salts from an exhaust gas temperature and/or a catalyst temperature; and
allowing a rich gas or a stoichiometric gas to flow through said passage to reduce and decompose the sulfurous salts by forming a reductive atmosphere when an amount of the sulfurous salts or the sulfuric salts existing in the catalyst estimated from the accumulated amounts under an oxygen rich atmosphere reaches a predetermined value.
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24. A method of recovering a NOx chemisorption reduction catalyst, arranged in an exhaust path of an internal combustion engine and detracted from the NOx purifying ability by adsorption or absorption of SOx in an exhaust gas, wherein
said method comprises the steps of detecting a concentration of nitrogen oxides in the exhaust gas at the timing when a predetermined time elapses after switching from operating under a reductive atmosphere condition to operation under an oxygen rich condition using a signal from a nitrogen oxide sensor arranged downstream of the exhaust gas purifying catalyst of the exhaust gas passage; estimating a decreasing ratio of nitrogen oxide purifying rate from said concentration of nitrogen oxides by calculation; and
allowing a rich gas or a stoichiometric gas to flow through said passage to reduce and decompose the sulfurous salts by forming a reductive atmosphere when an amount of the sulfurous salts and an amount of the sulfuric salts existing in the catalyst estimated from the decreasing ratio of nitrogen oxide purifying rate reaches a predetermined value.
Specification