ZEOLITE HAVING SPECIFIC RATIO OF DIVALENT COPPER IONS SUPPORTED THEREON, AND PREPARATION METHOD THEREFOR AND CATALYST COMPOSITION COMPRISING SAME
The present invention relates to zeolite containing Cu2+ (α) and Cu2+ (β) having different NO adsorption capacities loaded at a specific ratio, wherein the zeolite is chabazite (CHA)-type zeolite, particularly chabazite (CHA)-type zeolite loaded with divalent copper ions in which the NO adsorption area ratio of Cu2+ (α)/Cu2+ (β) after exposure to NO (nitrogen oxide) for 180 sec is 80% or more. In addition, the present invention relates to a method of preparing zeolite that is ion-exchanged in a slurry state and to a catalyst including the specified chabazite (CHA)-type zeolite.
- 1. A zeolite loaded with copper ions in which a Cu2+ (α
- )/Cu2+ (β
) ratio after exposure to NO for 180 sec in a NO DRIFTS spectrum is 80% or more.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
- )/Cu2+ (β
- 11. A method of preparing a Fe-ion-exchanged zeolite, the method comprising preparing a zeolite slurry by dispersing an iron precursor and H-zeolite in a slurry state and drying and calcining the zeolite slurry.
The present invention relates to zeolite containing divalent copper ions loaded at a specific ratio, a method of preparing the same, and a catalyst composition including the same, and more particularly, to a selective NOx reduction catalyst composition.
Chabazite-type zeolite, which is a selective NOx reduction catalyst provided in an exhaust gas treatment system, is a catalyst component used for reduction and removal of nitrogen oxide in automobile exhaust gas in the presence of an NH3 reducing agent. A hybrid selective reduction catalyst, disclosed in Korean Patent Application Publication No. 2014-0131401 by the present applicant, is provided in the form of a hybrid SCR catalyst having a double-layer structure in which a V2O5/TiO2 layer is formed at an upper layer or a lower layer and a zeolite layer impregnated with a metal (Cu or Fe) is formed at a lower layer or an upper layer, or in the form of a hybrid SCR catalyst having a single-layer structure in which V2O5/TiO2 and metal-impregnated zeolite are mixed. Furthermore, the above patent pertains to an SCR catalyst having improved ammonia occlusion capacity that is able to efficiently convert NOx to harmless substances in the acceleration/deceleration section of a diesel engine and to an exhaust gas discharge device using the same, in which diesel engine exhaust gas purification capability, particularly nitrogen oxide purification capability at low temperatures, is increased. Zeolite impregnated with a metal, especially Cu (hereinafter referred to as Cu-zeolite), rather than the hybrid catalyst, may be used alone as a NOx reduction catalyst.
Meanwhile, in order to apply Cu-zeolite as a NOx reduction catalyst for a vehicle, the zeolite catalyst composition is typically applied onto the inner walls of a honeycomb carrier. Briefly describing the overall process of preparing the catalyst composition, Cu-zeolite is purchased from a commercial source, mixed with deionized water, a binder and an additive, and dispersed to afford a Cu-zeolite catalyst composition, which is then applied on a carrier, dried and calcined, thereby completing a catalyst structure. Cu-zeolite, which is purchased from a commercial source, is typically prepared through liquid-phase ion exchange (hereinafter referred to as LPIE), and is specifically prepared by subjecting ammonium zeolite and a copper precursor to ion exchange by adjusting the temperature and acidity, followed by filtration, washing and drying, which is a method known in the art.
However, in the case of adjusting the amount of copper that is loaded in the catalyst composition, the problem of such diversity cannot be solved with commercially available Cu-zeolite. Meanwhile, the process of preparing a Cu-zeolite catalyst composition, in which Cu-zeolite is directly synthesized through liquid-phase ion exchange, rather than purchased, followed by mixing with deionized water, a binder and an additive and then dispersion as described above, is complicated, takes a long time, and increases manufacturing costs. Above all, there is a problem in that NOx high-temperature activity is lowered upon the preparation of a NOx reduction catalyst using Cu-zeolite that is prepared through conventional liquid-phase ion exchange or purchased.
With the goal of solving these problems, the present inventors have prepared Cu-zeolite using a novel process, not LPIE. The present inventors have prepared Cu-zeolite having a novel structure through a so-called in-slurry ion exchange (hereinafter referred to as ISIE) process. Unlike Cu-zeolite prepared through LPIE, the present inventors have ascertained that Cu-zeolite prepared through ISIE according to the present invention is configured such that Cu is selectively ion-exchanged at specific positions in the zeolite pores and is thus structurally differentiated from conventional zeolites. In chabazite (CHA)-type zeolite, Cu2+ ion-exchanged within small pores comprising 6 oxygen rings and Cu2+ ion-exchanged within large pores comprising 8 oxygen rings are represented as Cu2+ (α) and Cu2+ (α), respectively. Since NO (nitrogen monoxide) adsorbed to Cu2+ (α) and Cu2+ (β) shows DRIFTS (Diffuse Reflectance Infrared Fourier Transform Spectroscopy) absorption bands at different positions, the Cu2+ (α)/Cu2+ (β) ratio may be calculated accurately, and the structures thereof may be distinguished from each other. Therefore, Cu-zeolite was specified using, as a parameter, the NO adsorption ratio depending on the Cu2+ position. The present inventors adopted a spectral area ratio of Cu2+ (α)/Cu2+ (β) of the catalyst composition after exposure to NO (nitrogen monoxide) for 180 sec, as a new parameter. Chabazite (CHA)-type zeolite loaded with two or more copper ions in which the area ratio of Cu2+ (α)/Cu2+ (β) after exposure to NO for 180 sec is 80% or more is prepared through ISIE, and the preparation of the catalyst using CHA zeolite having the above novel structure is capable of achieving excellent high-temperature activity.
According to the present invention, zeolite containing divalent copper ions loaded at a specific ratio determined as a parameter is vastly superior in nitrogen oxide (NOx) purification activity at high temperatures, compared to conventional chabazite-type zeolite catalysts in which the adsorption ratio of Cu2+ (α)/Cu2+ (β) after exposure to NO for 180 sec is less than 80%. Moreover, ISIE confers a simple and rapid way to exchange copper ions in zeolite and facilitates control of the amount of copper that is loaded.
As used herein, the term “catalyst” or “catalyst structure” refers to a structure configured such that a catalyst composition including zeolite is applied to the inside of a typical honeycomb carrier or support. As is apparent by those skilled in the art, the carrier or support may indicate a structure, which may be made of an inorganic material or a metal and in which multiple passages are defined by multiple inner walls and the catalyst composition is applied on some or all of the inner walls. The catalyst structure is distinguished from what is meant by the term “catalyst composition”, and the catalyst composition is also distinguished from zeolite, which is a component thereof. Herein, the catalyst composition should be understood to include zeolite and a binder or an additive, such as an alkali metal or an alkaline earth metal, required for application onto the catalyst structure. In the present invention, “zeolite” means a structure in which a tetrahedron of (Si,Al)O4 has a three-dimensional skeleton and cavities due to the presence of apical oxygen, as will be easily understood by those skilled in the art, but in particular, chabazite-type zeolite having a SiO2/Al2O3 molar ratio of 5 to 50 is described as an example.
As copper-ion-exchanged chabazite-type zeolite, Cu-zeolite having a SiO2/Al2O3 molar ratio of 30 and an average particle diameter of 1.5 μm or more is known in the art. Cu-zeolite available from a commercial source is prepared through known LPIE. By catalyst manufacturers, a catalyst structure is manufactured in a manner in which commercially available Cu-zeolite is purchased, mixed with deionized water (DI water), a binder such as alumina, silica or zirconia, and an additive, and dispersed, thus preparing a Cu-zeolite catalyst composition, which is then applied on a honeycomb carrier, followed by drying and calcination. Here, the additive includes an alkali metal, an alkaline earth metal, a sugar or the like, which is known in the art. The completed honeycomb catalyst structure is attached to a vehicle engine exhaust system to reduce nitrogen oxides discharged from the engine to harmless substances.
The present inventors have prepared Cu-zeolite having a novel structure through a novel process called ISIE and a catalyst composition using the same. Compared to conventional Cu-zeolite obtained through LPIE, zeolite prepared through ISIE is very similar in terms of structure (SEM image), crystal structure (XRD pattern) and other properties (H2-TPR and NH3-TPD), but is different in the oxidation state of the ion-exchanged metal and the position thereof in zeolite pores, and thus the high-temperature activity of the catalyst according to the present invention can be confirmed to increase based on these parameter differences.
ISIE, which is a one-pot process used for the preparation of zeolite in the present invention, is different from conventional LPIE in that it obviates washing and filtration in the preparation of metal-impregnated zeolite. In LPIE, a soluble, especially water-soluble, Cu precursor, and ammonium zeolite are adjusted in temperature and acidity in a liquid phase, pretreated, washed and then filtered and thus copper-ion-exchanged, but in ISIE, a Cu precursor, preferably insoluble CuO, and H-zeolite are subjected to ion exchange through contact and milling in a slurry state, and thus ISIE is understood to be a process that obviates additional washing and filtration. Specifically, DI water is added with CuO, H-zeolite and a binder, for example, a Zr material, stirred at room temperature for 10 min or more, milled, further added with an additive, and dispersed to afford a Cu-zeolite catalyst composition, which is then applied on a honeycomb carrier, followed by drying and calcination, thereby preparing a catalyst structure. Although not particularly limited in theory, CuO is deemed to undergo slow copper ionization through slurry milling and to be transferred to the proper position in zeolite. The zeolite prepared through ISIE according to the present invention is compared with the conventional zeolite prepared through LPIE.
The Case-1 sample is zeolite that has a SiO2/Al2O3 molar ratio of 30 and in which 3 wt % of CuO is loaded based on the total weight thereof, and the Case-2 sample is zeolite that has a SiO2/Al2O3 molar ratio of 5 and in which 2.5 wt % of CuO is loaded based on the total weight thereof and potassium and calcium oxides are contained as additives in amounts of 1 to 5 wt %. As shown in
In the present invention, the crystal structures of zeolites obtained through ISIE and LPIE are compared.
As shown in
However, as will be described below, the zeolite prepared in the present invention is different in terms of NOx reduction, in particular NOx reduction activity at high temperatures, from conventional zeolite, and thus the present inventors have sought to determine the parameters that distinguish them structurally.
As disclosed in documents, two divalent copper ions are known to be present depending on the NO adsorption capacity.
As shown in
With reference to
Below is a description of the method of preparing the catalyst composition schematically shown in
It is preferred that these materials be mixed to afford the material composition for chabazite-type zeolite. In the material composition, the SiO2/Al2O3 molar ratio preferably falls in the range of 16 to 100. Given the molar ratio of the material composition ranging from 16 to 100, it is easy to obtain chabazite-type zeolite having a SiO2/Al2O3 molar ratio of 5 to 50. The material composition comprising water, the silica material, the alumina material, and the structure-directing agent is preferably crystallized in a sealed pressure vessel at a temperature between 100 and 200° C. for a sufficient period of time, thus obtaining chabazite-type zeolite. The chabazite-type zeolite thus obtained is configured such that one or both of the structure-directing agent and the alkali metal may be contained in the pores thereof. Hence, these are preferably removed as necessary. The removal of alkali metal, etc. may be performed through exchange treatment using an acidic solution, pyrolysis or appropriate combination thereof, thereby preparing H-zeolite. In the preparation method, chabazite-type zeolite is provided by way of example, and 8-membered oxygen-ring small-pore zeolite, for example, LTA, AEI, AFT, AFV, AFX, KFI, SAV, SFW, TSC, FAU, MFI, BEA, FER, or MOR, may be applied.
The H-zeolite synthesized above or commercially purchased is mixed with a Cu precursor such as CuO, a binder such as Zr acetate, and an additive, and is dispersed, thus preparing a Cu-zeolite catalyst composition. As the Cu precursor, copper acetate, copper nitrate, or copper sulfate may be used. CuO is understood to be ion-exchanged through contact and milling in a slurry state with the H-zeolite. DI water is added with CuO, H-zeolite and Zr acetate, stirred at room temperature for 10 min or more, and then milled. Also, the additive is added thereto and dispersed, thus preparing a Cu-zeolite catalyst composition in a slurry state, which is then applied on the inner walls of a honeycomb carrier, understood by those skilled in the art, dried and calcined at 450° C., resulting in a catalyst structure. In the present invention, the additive may include an alkali metal, an alkaline earth metal, a sugar or the like, which is known in the art. In an embodiment of the present invention, as described above, the Case-1 sample is a catalyst composition including zeolite having a SiO2/Al2O3 molar ratio of 30 and loaded with 3 wt % of CuO based on the total weight thereof, and the Case-2 sample is a catalyst composition including zeolite having a SiO2/Al2O3 molar ratio of 5 and loaded with 2.6 wt % of CuO based on the total weight thereof and added with 1 to 5 wt % of potassium and calcium oxides as additives. The completed honeycomb catalyst structure is attached to a vehicle engine exhaust system to reduce nitrogen oxides into harmless substances.
Moreover, an embodiment in which Fe is exchanged in lieu of Cu was performed in the same manner as above. The results are shown in