CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. National Stage of International Patent Application PCT/CN2016/091711, filed Jul. 26, 2016 and claims priority to International Patent Application No. PCT/CN2015/097704, filed Dec. 17, 2015. The disclosures of each of the applications noted above are incorporated herein by reference in their entirety.

TECHNICAL FIELD

Generally, the present invention relates to a catalyst for nitrogen oxides (NOx) removal. More specifically, the present invention relates to a selective catalytic reduction (SCR) catalyst containing vanadium and antimony on a support, preparation process thereof, and use thereof for NOx removal.

BACKGROUND

NOx emitted as exhaust gases from mobile source such as vehicles and stationary source such as a power plant would be harmful to environment and human beings. In order to remove NOx from exhaust gases, catalytic reducing methods have heretofore been developed. The catalytic reducing methods are suitable for dealing with large quantities of exhaust gases, and of these, a process comprising adding ammonia as a reducing agent to catalytically reduce NOx selectively to N2was reported to be superior. The catalysts used in such selective catalytic reduction (SCR) are required to reduce NOx over a broad temperature range and especially at a temperature as low as possible below 300° C.

SCR catalysts which are vanadium (V)/antimony (Sb) binary systems based on a support, such as V/Sb/TiO2have been disclosed, for example, in KR 101065242 B1, US 2009/143225 A1 and U.S. Pat. No. 4,221,768. It is believed that the incorporation of Sb as a promoter in conventional V-containing catalysts can result in improved SCR performance of the catalysts.

U.S. Pat. No. 8,975,206 B2 discloses a catalyst composition comprising a vanadate represented by XVO4/S, in which XVO4stands for Bi-, Sb-, Ga- and/or Al-vanadate, and S is a support comprising TiO2. Among others, VSbO4supported on TiO2/WO3/SiO2is given as an example, which is prepared by mixing V and Sb source solutions, drying at 120° C. and calcining at 550° C. for 20 hours to obtain VSbO4which is then supported on TiO2/WO3/SiO2. No XRD pattern showing the structure of the vanadates, especially of VSbO4is disclosed in the patent.

WO 2013/179129 A2 discloses a SCR filter comprising a substrate in the form of a wall flow filter and a catalyst carried on said substrate, the catalyst comprising a support and a vanadate component. Said vanadate has a structure defined by the formula of (Ax)(Ty)(Rz)VO4, wherein “A” is an alkaline earth metal, “T” is a transition metal, “R” is a rare earth metal, and “x”, “y” and “z” are molar ratios of respective metals to vanadium with 0≤x≤1, 0≤y≤1, 0≤z≤1 and x+y+z=1. This patent application only discloses FeVO4as the vanadate component. The SCR performance of the wall flow filter comprising FeVO4carried on the substrate is not discussed in the application.

In spite of the known SCR catalysts, there is still a need for SCR catalysts that exhibit excellent activity for NOx removal, especially in mobile and stationary exhaust gas emission applications.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a novel SCR catalyst with improved NOx removal, especially in mobile and stationary exhaust gas emission applications. The object can be achieved by a catalyst composition, a method for the preparation thereof, use of the catalyst composition for selective catalytic reduction of nitrogen oxides. Particularly, the present invention relates to following aspects.

1. Use of a catalyst composition comprising:a support comprising TiO2,a composite oxide containing vanadium and antimony, which has a rutile-type structure different from VSbO4and V0.92Sb0.92O4as determined by X-ray diffraction (XRD) analysis with CuKα radiation, andoptionally, one or more selected from the group consisting of oxides of silicon, oxides of vanadium and oxides of antimony,for selective catalytic reduction of nitrogen oxides.

2. Use according to the above aspect 1, wherein the composite oxide containing vanadium and antimony is characterized by an XRD diffraction peak of (110) or (101) plane at higher 2θ than those of VSbO4and V0.92Sb0.92O4by at least 0.1°.

3. Use according to the above aspect 2, wherein the composite oxide containing vanadium and antimony is characterized by an XRD diffraction peak of (101) plane at higher 2θ than those of VSbO4and V0.92Sb0.92O4by at least 0.2°, preferably at least 0.3°, and more preferably at least 0.5°.

4. Use according to any of the above aspects 1 to 3, wherein the composite oxide containing vanadium and antimony is characterized by an XRD diffraction peak of (110) plane at 2θ in the range of from 27.25° to 29.00° and an XRD diffraction peak of (101) plane at 2θ in the range of from 35.43° to 37.00°.

5. Use according to any of the above aspects 1 to 4, wherein vanadium, including those in both the composite oxide vanadium and antimony and the optional oxide(s) of vanadium, is present in the catalyst composition in the range of 0.5 to 6% by weight, preferably 1 to 4.5% by weight, and more preferably 2 to 4% by weight, calculated as elemental V; and wherein antimony, including those in both the composite oxide vanadium and antimony and the optional oxide(s) of antimony, is present in the catalyst composition in the range of 0.8 to 16% by weight, preferably 3.5 to 14% by weight, and more preferably 5 to 10% by weight, calculated as elemental Sb.

6. Use according to any of the above aspects 1 to 5, wherein the catalyst composition is in a shaped form, preferably in form of extrudate, or is carried on a substrate.

7. Use according to the above aspect 1, wherein the nitrogen oxides are present in exhaust gases from an internal combustion engine such as diesel engine, a power plant or an incinerator.

8. A process for preparing the catalyst composition as defined in any of the above aspects 1 to 6, which includes steps of:(i) mixing a vanadium/antimony oxide and optionally a silicon source with a support comprising TiO2in a solvent to obtain a suspension;(ii) optionally, applying the suspension onto a substrate;(iii) drying at a temperature in the range of 80 and 250° C.;(iv) calcining at a temperature of at least 500° C.

9. The process according to the above aspect 8, wherein the calcining in step (iv) is conducted at a temperature in the range of higher than 500° C. to 700° C., more preferably 550° C. to 700° C., still preferably 600° C. to 700° C., and most preferably 650° C. to 700° C.

10. The process according to the above aspect 8 or 9, wherein the vanadium/antimony oxide used in step (i) is prepared by(a) providing a suspension comprising vanadium oxide(s) and antimony oxide(s); and(b) drying the suspension to obtain the vanadium/antimony oxide at a temperature in the range of 80° C. to 250° C.

11. The process according to the above aspect 8 or 9, wherein the vanadium/antimony oxide used in step (i) is prepared by(a′) providing a suspension or solution comprising a vanadium source and an antimony source;(b′) precipitating and separating the vanadium/antimony oxide from the suspension or solution; and(c′) optionally, drying at a temperature in the range of 80° C. to 250° C.

12. The process according to any of the above aspects 8 to 11, which does not comprise step (ii), and optionally comprises a step of shaping in order to obtain the catalyst composition in a shaped form.

13. A catalyst composition obtained/obtainable by the process according to any of the above aspects 8 to 12.

14. Use of the catalyst composition according to the above aspect 13 for selective catalytic reduction of nitrogen oxides.

15. Use according to the above aspect 14, wherein the nitrogen oxides are present in exhaust gases from an internal combustion engine such as diesel engine, a power plant or an incinerator.

