METHOD OF PREPARATION OF A MONOLITHIC CATALYST FOR SELECTIVE CATALYTIC REDUCTION OF NITROGEN OXIDES

Abstract

Method of preparing monolithic SCR catalyst with a plurality of gas flow channels comprising the steps of (a) providing a monolithic shaped substrate with a plurality of parallel gas flow channels; (b) coating the substrate with a wash coat slurry comprising vanadium oxide precursor compounds and titania and optionally tungsten oxide precursor compounds; and (c) drying the thus coated substrate with a drying rate of 5 mm/min or less along flow direction through the gas flow channels; and (d) activating the dried coated substrate by calcining.

Claims

1. Method of preparing monolithic SCR catalyst with a plurality of gas flow channels comprising the steps of (a) providing a monolithic shaped substrate with a plurality of parallel gas flow channels; (b) coating the substrate with a wash coat slurry comprising vanadium oxide precursor compounds and titania; and (c) drying the thus coated substrate with a drying rate of 5 mm/min or less along flow direction through the gas flow channels; and (d) activating the dried coated substrate by calcining.

2. The method of claim 1, wherein the drying rate is controlled by controlling drying air flow rate to 0-3 m/s and a drying temperature of below 70? C.

3. The method of claim 1, wherein the drying of the coated substrate is performed by means of micro wave or long wave heating.

4. The method of claim 1, wherein the drying of the coated substrate is performed by placing the substrate in a position horizontally relative to gravity.

5. The method of claim 1, wherein the wash coat slurry further comprises tungsten precursor compounds.

6. The method of claim 1, wherein the monolithic shaped substrate is composed of a number of corrugated sheets stacked upon each other.

7. The method of claim 6, wherein each of the corrugated sheets are provided with a flat sheet prior to be stacked.

8. The method of claim 1, wherein the corrugated shaped substrate is formed by rolling up a single corrugated sheet.

9. The method of claim 8, wherein the single corrugated sheet is provided with a fiat sheet prior to rolling up.

10. The method of claim 6, wherein the corrugated sheets are made of fiberglass.

11. The method of claim 1, wherein monolithic shaped substrate is obtained by extrusion of ceramic material.

12. The method of claim 1, wherein the activated coated substrate comprises vanadium pentoxide and titania.

13. The method of claim 12, wherein the activated coated substrate further comprises tungsten trioxide.

14. The method of claim 1, wherein the monolithic SCR catalyst is in form of a wall flow filter.

15. The method of claim 1, wherein the drying air rate is 0 and the drying is performed at room temperature.

Description

EXAMPLES

Example 1

[0045] A honeycomb structured substrate was washcoated with a titania slurry containing containing 1.95 wt % ammonium metavanadate and 9.66 wt % ammonium meta-tungstate to a wash coat layer thickness of 0.3-0.5 mm. The washcoated substrate was dried with warm air at 50? C. and an air flow rate 2 m/sec resulting in a drying rate of 0.8-1.2 mm/min and calcined at 450? C. for 2 h. After drying the washcoated substrate was calcined at 450? C. for 2 hours. The distribution profile of vanadium and tungsten over wall thickness in the calcined substrate is shown in FIG. 3. As seen in FIG. 3, the slow dried substrate has almost no concentration gradients in the distribution of tungsten across the thickness of the washcoat, and the concentration gradient of vanadium is very much reduced compared to the gradients in the fast dried substrate prepared in the following comparison example (see FIG. 2)

Comparison Example

[0046] A washcoated honeycomb structured substrate was prepared as in Example 1. The substrate was dried with warm air at 250? C. and an air flow rate of 2 m/sec resulting in a drying rate of 6-8 mm/min and calcined at 450 for 2 h and calcined at 450? C. for 2 hours.

Example 2

[0047] The SCR activity of the honeycomb catalysts prepared in Example 1 and in the Comparison Example was tested at temperatures between 200 and 550? C. at a NO/NH.sub.3 of 1.2. The test results are shown in FIG. 1. As apparent from FIG. 1, the honeycomb catalyst dried at a rate of 0.8-1.2 mm/min has an improved SCR activity at temperatures above 350? C. compared to the catalyst dried at a higher drying rate of 6-8 mm/min.