AU615375B2

AU615375B2 - A catalyst for the selective reduction of nitrogen oxides with ammonia

Info

Publication number: AU615375B2
Application number: AU50026/90A
Authority: AU
Inventors: Reinhold Dr. Brand; Bernd Dr. Engler; Wolfgang Dr. Honnen; Edgar Dr. Koberstein; Johannes Dr. Ohmer
Original assignee: Degussa GmbH
Current assignee: Evonik Operations GmbH
Priority date: 1989-02-28
Filing date: 1990-02-21
Publication date: 1991-09-26
Anticipated expiration: 2010-02-21
Also published as: EP0385164B1; BR9000900A; RU2058814C1; EP0385164A3; ATE95443T1; EP0385164A2; DE3906136C1; ES2046549T3; DK0385164T3; AU5002690A; DD296854A5; JPH02290250A; CA2010970A1; DE59002961D1; KR900012674A

Abstract

A catalyst for the selective reduction of nitrogen oxides by means of ammonia contains, in addition to titanium oxide as component A), at least one oxide selected from the group comprising W, Si, B, Al, P, Zr, Ba, Y, La and Ce and at least one oxide selected from the group comprising V, Nb, Mo, Fe and Cu as component B), the atomic ratio between the elements of the components A) and B) being 1 : 0.001 to 1. The catalyst is obtainable by kneading reactive titanium oxide of high specific surface area comprising predominantly anatase with the substances comprising component B) or their precursors with the addition of processing agents to give a homogeneous kneaded mass, extruding this, drying the extrudate and calcination in air at 300 - 800 DEG C.

Description

i 615375 S F Ref: 120755 FORM COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Class Int Class .0 00 0 *000

S.

@000 0 0000 00 Complete Specification Lodged: Accepted: Published: Priority: Related Art: Name and Address of Applicant: Degussa Aktiengesellschaft Weissfrauenstrasse 9 D-6000 Frankfurt am Main FEDERAL REPUBLIC OF GERMANY Address for Service: Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Complete Specification for the invention entitled: A Catalyst for the Selective Reduction of Nitrogen Oxides with Ammonia The following statement is a full description of this invention, including the best method of performing it known to me/us 5845/4 89 116 KY Abstract

L-

A catalyst for the selective reduction of nitrogen oxides with ammonia In addition to titanium oxide as component a catalyst for the selective reduction of nitrogen oxides with ammonia contains at least one oxide of W, Si, B, Al, P, Zr, Ba, Y, La, Ce and at least one oxide of V, Nb, Mo, Fe, Cu as component B) the atomic ratio between the *elements of components A) and B) being from 1 0.001 to 1.

The catalysts can be obtained by kneading reactive titanium oxide having a high specific surface of, predominantly, o. anatase with the substances of component B) or precursors thereof with addition of processing aids to form a homogeneous kneaded paste extruding this paste, drying the extrudate and calcining it in air at 300 to 800"C.

S O.S

S

3 89 116 KY A catalyst for the selective reduction of nitrogen oxides with ammonia Description Nitrogen oxides which are formed in combustion processes are among the main causes of acid rain or photosmog and the ensuing damage to the environment. Along with fluorochlorocarbons, nitrogen oxides in particular are suspected of being responsible for the observed depletion of the 0oozone layer above the polar regions.

o* Sources of nitrogen oxide emission are vehicle traffic, stationary combustion engines, power stations, thermal 0000 power stations, steam generators for industrial purposes *000 0 and industrial production plants.

Although, in boiler-fired power stations, a reduction in the nitrogen oxide concentration of the exhaust gases can be obtained by using very pure fuels or by optimizing i the combustion systems (primary measures), there are both technical and economic limits to these primary measures.

•"'Accordingly, secondary measures also have to be taken to keep to the legally stipulated emission limits. Secondary *measures for nitrogen oxide reduction are, typically, catalytic reduction processes in which ammonia is generally used as a selective reducing agent.

known There are already numereus catalysts for reducing nitrogen oxide emission by catalytic reduction. Thus, DE- ASS 12 59 298, 12 53 685 and 11 15 230 describe oxidic catalysts with no noble metal content while DE-OS 22 14 604 describes oxidic catalysts containing noble metals.

DE-PS 24 58 888 describes another catalyst which consists of an "intimate mixture" of the following components: A) titanium in the form of oxides B) at least one metal from the group 4 89 116 KY B-i iron and vanadium in the form of oxides and/or from the group B-2 molybdenum, tungsten, nickel, cobalt, copper, chromium and uranium in the form of oxides C) tin in the form of oxides D) metals from the group consisting of beryllium, magnesium, zinc, boron, aluminium, yttrium, rare earth elements, silicon, niobium, antimony, bismuth and manganese in the form of oxides.

The components are present in atomic ratios of A B C S. D of 1 0.01 to 10 0 to 0.2 0 to 0.15. nitrogen oxide o A catalyst having this composition is used for the reduction gas mixtures containing oxygen and ammonia at temperatures in the range from 150 to 550°C and at space 000 velocities of 300 to 100,000 h These catalysts may be produced by measures known per se. However, these measures must always guarantee that the components A) and B) and, optionally, C) can be obtained as an intimate mixture in the form of their oxides. The fol- .lowing are mentioned as typical examples of such production processes: la: homogeneous dissolving process ib: co-precipitation processes 2 combinations of the dissolving and precipitation processes 3 mixed precipitate processes.

Solutions and/or precipitates, such as for example 0* hydroxides or aqueous gels, are used as precursors of components B) and being intimately mixed and then subjected to calcination. The precursors are pyrolized, giving the desired intimate mixture of the oxides of the components critical to the catalysis process. The calcination temperature has to be in the range from 300 to 800°C.

Below 300°C, it is not possible to obtain an intimate 'II_ I_ I: i i i i. i 89 116 KY mixture of the oxides and therefore no active catalyst; above 800°C, sintering occurs and results in loss of the active catalyst surface.

The starting materials used for titanium as component A) include, for example, various titanium acids, titanium hydroxide and various titanium salts, such as halides, titanium sulfate, titanyl sulfate and the like. Organic compounds of titanium, for example titanium alkoxides, may also be used as starting material for the titanium. Titanium oxide in the calcined rutile or anatase form is not suitable.

.g The catalyst material described in DE-PS 35 31 809 is *based on a further development of these catalyst production processes described in DE-AS 24 58 888. Titanium dioxide 15 is used as starting material for the production of this :eo catalyst material and is ground together with vanadium oxide and one or more oxides of the elements tungsten, molybdenum, phosphorus, chromium, copper, iron, uranium and the Rbped to at least one heat treatment. !-Fkthi S 20 heat tratm c the tungsten and molybdenum are completely C o} or partly replaced by phosphorus in the form of its oxides or phosphates. The mills used are preferably eccentric disc mills and ring chamber mills. The calcination step S"takes place at a temperature in the range from 200 to 900°C.

With all hitherto known catalysts of this type, com- eeeo• ponents A) and B) (for example A Ti; B W, Mo. etc.) must be present in the form of an intimate mixture of their oxides. This mixture is then subjected to a shaping process from which the catalysts can be obtained in the form of loose material or honeycomb monoliths by compression moulding or extrusion.

This means that shaping of the catalyst, for example by extrusion, has to be preceded by a process of which the object is to form the intimate mixture as starting materi- C I C I

S.

7 89 116 KY *see 500 00S

S

6 .0 es @50 0 00 0 So S

SO

00 al. This procedure, which is widely used at the present time, is attended by the following disadvantages: elaborate, multistage, energy-intensive process steps are necessary; the production of the intimate mixture in accordance with DE-AS 24 58 888 is not environment-friendly on account of emission and wastewater problems; the operation of mills for grinding activation is energy-intensive and requires elaborate noise control measures and dust control systems; the preliminary process steps for forming the intimate mixture are a serious cost factor in the production of the catalyst.

Accordingly, the problem addressed by the present invention is greatly to simplify and, hence, distinctly to reduce the cost of catalyst produCt~iol e saving process steps in the production of so-called whee catalysts (which consist throughout of catalytically active material) for the selective reduction of nitrogen oxides in oxygencontaining exhaust gases in the presence of ammonia. In addition, the invention seeks to enable the properties of the catalyst to be directly and finely controlled through the management of the process.

This problem is essentially solved by the choice of certain titanium oxide materials and by processing these materials by kneading; there is no longer any need for the already known measures for the formation of an intimate oxide mixture.

The subject of the invention is the teaching expressed in the claims.

Suitable titanium oxides are reactive high-surface titanium oxides having a specific BET surface of from 40 to 500 m 2 /g which are completely or predominantly present in anatase form. These materials may be commercial products produced by precipitation or by flame hydrolysis. Apart L i i -I 89 116 KY from their high specific surface, these generally highly disperse products have a very narrow particle size distribution with an average primary particle size of the order of 30 nm.

The individual elements of group B) may be used, for example, in the form of the following starting compounds: tungsten oxide, ammonium para- or meta-tungstate, silicon dioxide, silicotungstic acid, silica, boron oxide, boric acid, aluminium oxide, phosphorus oxide, ammonium phosphate, phosphotungstic acid, phosphomolybdic acid, zirconium dioxide, zirconium phosphate, barium oxide, yttrium oxide, lanthanum oxide, cerium acetate, cerium nitrate, cerium oxide, borotungstic acid, vanadium oxide, vanadyl oxalate, ammonium metavanadate, vanadotungstic acids, vanadomolybdic acids, vanadophosphomolybdic acids, phosphovanadic acid, niobium oxide hydrate, niobium oxalate, niobium vanadic acids, ammonium molybdate, molybdenum oxide, iron oxide, iron phosphate, iron hydroxide, organic iron salts, such as iron oxalate, copper acetate, copper- (II) oxide, Cu-, Ce-, La-containing heteropoly acids, etc.

The substances mentioned may be used in the form of solutions or even in the form of solid substances.

Apart from the actual catalyst material, a number of additives known per se are required for the production of solid type the whele catalysts according to the invention.

Deionized water, aqueous ammonia solution, monoethanolamine and alcohols may be used as the moistening agent.

Glass fibers of various sizes, for example, may be used as supporting materials.

Suitable binders, which provide the paste to be produced with sufficient stability in the so-called green state after shaping, are cellulose derivatives such as, for example, carboxymethyl cellulose or even unsubstituted celluloses.

Polyethylene, polypropylene, polyvinyl alcohol, poly-

-J

8 89 116 KY ethylene oxide, polyacrylamide or polystyrene may also be used as the binder.

To facilitate compression moulding or to improve extrudability, moulding aids and/or lubricants such as, for example, bentonites, aluminas, organic acids, paraffin, waxes, silicone oils, are added.

size Finally, the porosity (pore volume, poreVdistribution) of the whole catalysts may be adjusted as required by the addition of suitable air-entraining agents. Additives such as these are, for example, finely divided carbons or wood pulp, which burn out at the calcination temperatures applied.

Kneading units are used for intensively kneading the starting materials to a homogeneous kneaded paste. Kneadj 15 ers with sigma or masticator blades are preferred. The use j of a certain titanium oxide in accordance with the invention in conjunction with an intensive kneading step for preparing the catalyst paste affords considerable advantages over the conventional production process. Thus, there is no longer any need for elaborate, environmente. polluting and, hence, expensive process steps. Co-precipitation and grinding processes for preparing an intimate oxide mixture are no longer necessary. This leads to a S. distinct reduction in production costs and also eliminates dependence on expensively produced starting materials.

In addition, contraction, a key parameter in regard to solid type the tendency of whole catalysts to crack and in regard to S. their breaking strength, can be regulated as required by the use of suitable starting materials and by adaptation of the kneading process in regard to intensity, temperature and time, including intermediate conditioning steps (cf.

claims 3 to In addition, the new catalyst production process, by saving several process steps, guarantees more direct and, at the same time, more flexible control of the catalyst r II i i 89 116 KY properties. Thus, the resistance of the catalysts to sintering can be improved by the choice of a suitable stabilizer component from group B 1 This is reflected in the fact that the high BET surface of the final catalyst remains substantially constant under in-use conditions and in the fact that the temperature-induced phase transition of the titanium dioxide from the anatase to the rutile modification is suppressed. Dictinotly longer useful liv of the eatalysts obtainable in accordance with the zri-a-t.c are ho dirog ct rcult f th.. prcperties.

Figure 1 (for Example 13) illustrates the reduction in activity fall-off during long-term use in flue gases of dry coal-burning plants with operating temperatures above 300°C if her SiO z is used as stabilizer in the catalyst.

'15 Through the physicochemical properties of the starting materials (TiO, anatase, stabilizers from group B 1 activators from group B 2 and through the choice of the other additives and through processing in a kneader in accordance size with the invention, the pore volume and pore iadius diso'20 tribution of a given kneaded paste can be controlled by e0** empirical variation of its moisture content during the size kneading process. The pore rad s- distribution can be varied within wide limits over the mesopore and macropore range, mono- bi- and trimodal pore r~ae distributions and transitional forms in between being adjustable as required.

The correct choice of these parameters leads to a consid-

C

erable increase in the activity of the catalyst. However, size poreVdistribution and pore volume also have a major influence.on resistance to poisoning and hence directly on the stationary Li etime uceful life of the catalysts.

In this connection, particular significance is also attributed to the pK value of the solid surface. In the catalyst according to the invention, the pK value may be varied within wide limits through the choice of the stabilizers or activators. The use of heteropoly acids as As a direct result of these properties catalysts obtainable in accordance with the claims have distinctly longer stationary lifetimes.

I I ~r 89 116 KY activators and/or stabilizers is particularly mentioned in this regard. Interestingly, it has been found that, when used in the particularly problematical flue gases of coalfired slag-tap furnaces, catalysts made of these materials enri che show a distinctly lower tendency to take up- arsenic and other catalyst poisons by comparison, for example, with the catalysts according to DE-PS 25 58 888. This is attributable to increased poisoning resistance through reduced heavy metal adsorption to the catalyst surface. As a result, catalysts can be used over industrially useful periods in the high-dust operation of coal-fired slag-tap na fur-aces. By contrast, known comparison catalysts are rapidly deactivated mainly by heavy metals present in the *flue gas.

Figures 2 and 3 show the surprisingly high increase in S activity of catalysts according to the invention by como• parison with a catalyst conventionally produced in accordance with Comparison Example 1.

The invention is further illustrated by the following Examples.

.,The catalysts were tested both in dust-free model exhaust gases in a laboratory test plant and also in the exhaust gas of an oil-burning plant. In addition, longterm tests were carried out in the flue gas of a dry coalburning plant.

The catalyst tests were carried out at temperatures in the range from 200 to 500°C. The space velocities were 6 between 10,000 and 40,000 h i 1 The reducing agent, ammonia, and the nitrogen oxide were used in the particular molar ratio feound to be favourable of 0.6 to 1.6 -afi preferably 0.8 to 1.2? which was found to be favourable.

Comparison Example Litres deionized water, 6 kg 15% by weight aqueous

NH

3 solution, 1.8 kg monoethanolamine and a solution of r I I-

I

89 116 KY

S

a 0.

0 Cr

S

*5 C a II I ammonium metavanadate corresponding to 350 g V 2 5 O were added to 35 kg of an intimate mixture of the oxides TiO 2 and W0 3 in a ratio by weight of 9 1 prepared in accordance with DE-PS 24 58 888. The mixture is intensively kneaded with a varying moisture content and at temperatures of 70 to 620 g SiO 2 1.4 kg alkali-free clay and 3.5 kg glass fibres (length 1 to 8 mm) were then successively added.

The mixture is kneaded for 6 to 8 hours to form a homogeneous kneaded paste, 410 g polyethylene oxide, 410 g carboxymethyl cellulose, 230 g lactic acid and 11.5 kg fully deionized water additionally being added to establish the plasticity required for subsequent shaping.

The catalyst paste is then extruded in an extruder to honeycomb monoliths with passages of square cross-section (cell division: 3.4 mm or 7.4 mm).

The extrudates are dried at an increasing temperature of 20 to 60"C in an air-conditioned drying chamber and, after a stepwise increase in temperature, are finally calcined for 24 hours at 620"C.

Examples 1 to 9 The composition of the catalysts is shown in Table 1.

The following basic procedure was adopted to prepare the catalysts: 4.4 kg ammonium paratungstate (APW), 22 litres deionized water, 7.5 kg 15% by weight aqueous NH 3 solution, 1.8 kg monoethanolamine and a solution of ammonium metavanadate corresponding to 390 g V 2 0 5 are added to 35 kg of the TiOz anatase mentioned in claim 1 with a BET surface of 98 m 2 /g.

670 g SiO 2 2.5 kg glass fibres (length 1 to 8 mm) and kg alkali-free clay are then successively added with intensive kneading at a temperature in the range from 60 to The mixture is kneaded for 5 to 7 hours to form a homogeneous kneaded paste (Werner Pfleiderer LUK kneader), 450 g polyethylene oxide, 450 g carboxymethyl *1 *S.

S 30 12 89 116 KY cellulose, 250 g lactic acid and 12.3 litres "eionized water being additionally incorporated to establish the necessary plasticity. To fine-tune the moisture content and the plasticity of the kneaded paste, more ammonia water S 5 had to be added before the end of the kneading process.

The catalyst paste is then extruded in an extruder to honeycomb monoliths with passages of square cross-section (cell division: 3.4 mm). After drying at an increasing temperature of 20 to 60°C in an air-conditioned drying chamber, followed by a stepwise increase in temperature, the mouldings are calcined for 24 hours at 620'C.

I In Examples 6 to 9, TiO 2 -P-25 produced by flamehydrolysis (Degussa), tungsten oxide or boron oxide and Nb 2 0 5 the latter in the form of niobium oxalate dissolved in water, were respectively used instead of TiO 2 anatase, ammonium paratungstate (APW) and ammonium metavanadate (AMV) i Se •e tj> a SSd C S C C S C 116 K 13 89116tiKY Table 1 Example Comp. A Comp. B 1 Ratio by weight Comp. B 2 Proportion of B 2 oxide A oxide/B 1 oxide in g/100 g A-B 1 mixed oxide 1 Anatase APW 9 1 AMV 2 Anatase APW 9.5 0.5 AMV 3 Anatase APW 9.9 0.1 AMy 4 Anatase APW 9 1 AMV Anatase APW 9 1 AVL 6 Anatase W0 3 9 1 AMV 7 P-25 W0 3 9 1 AMV 8 Anatase B 2 0 3 9.7 0.3 AMV 9 Anatase APW 9 1 Nb 2

(C

2 0 4 5 I 14 89 116 KY Examples 10 to 13 4.4 kg ammonium paratungstate (APW) and 10 kg 15% by weight aqueous NH 3 solution are added to 35 kg of the TiOz anatase mentioned in claim 1, BET surface 75 m 2 in a kneader which has been switched on. The suspension obtained is kneaded for 3 hours at 80*C to dryness (residual moisture 5 to 10% by weight). 22 Litres deionized water, kg 15% by weight aqueous NH 3 solution, 1.8 kg monoethanolamine and a solution of ammonium metavanadate (AMV) corresponding to 390 g V 2 0 5 are then added to the mixture thus obtained. The resulting paste is further processed as described in Examples 1 to 9 and extruded to form the same honeycomb monoliths. The monoliths are also dried and calcined by the method described in Examples 1 to 9.

*15 In Example 11, the ammonium metavanadate was replaced by ammonium molybdate (AM) and, in Examples 12 and 13, the ammonium paratungstate was replaced by BaO or SiO 2 as shown in Table 2.

A

R

:o 0. :0 .0 000 0, 0 0, 000 89 116 KY Table 2 Example Comp. A Comp. B 1 Ratio by weight Comp. B 2 Proportion of B 2 oxide A oxide/B 2 oxide in g/1OO g A-B 1 mixed oxide Anatase APW 9 1 AMV 11 Anatase APW 9 1 AM 12 Anatase BaO 9.5 0.5 AMV 13 Anatase SiO 2 9 1 AMl 16 89 116 KY Examples 14 to 17 kg aluminium oxide and 12.5 kg 50% by weight aqueous NH 3 solution are added to 35 kg of the TiO 2 anatase mentioned in claim 1 with BET surface of 40 m/g. The paste is kneaded for 2 to 3 hours at 80"C to a residual moisture content of 5 to 10% by weight. The powder is then precalcined for 2 hours at 400*C.

22 Litres deionized water, 75 kg 50% by weight aqueous

NH

3 solution, 2.0 kg monoethanolamine, 210 g pulp (coarsefibre cellulose) and then a solution of ammonium metavanadate corresponding to 390 g V 2 0 5 are added to the precalcined oxide mixture in the kneader. 2.3 kg alkali-free clay, 2.2 kg glass fibres (length 1 to 8 mm), 200 g polyethylene oxide, 2 00 gcarboxymethyl cellulose and 250 g additionaLLy 15 lactic acid are then added with intensive kneading at 60 to 90*C. The mixture is kneaded for 5 to 7 hours to form a

•S

homogeneous kneaded paste, more ammonia water being added to establish the necessary plasticity. Finally, the catalyst paste is extruded in an extruder to honeycombs having square passages (cell division: 7.4 mm). After drying at 5 an increasing temperature (20 to 60°C) in an air-conditioned drying chamber, followed by a stepwise increase in temperature, the mouldings are calcined for 24 hours at 700*C.

In Examples 15 to 17, the aluminium oxide was replaced by ammonium paratungstate or lanthanum oxide and, in Example 16, the ammonium metavanadate was replaced by copper(II) acetate dissolved in water, as shown in Table 3.

00 se 0* 00 0 0* 0 17 89 116 KY Table 3 Example Comp. A Comp. B 1 Ratio by weight Comp. B 2 Proportion of B 2 oxide A oxide/B 1 oxide in g/100 g A-B 1 mixed oxide 14 Anatase A1 2 0 3 9 1 AMV Anatase APW 9 1 AMV 16 Anatase APW 9.5 0.5 CU (CH 3 COO) 2 17 Anatase La 2 0 3 9.5 0.5 AMV 18 89 116 KY Examples 18 to 21 kg zirconium oxide, 390 g V 2 0 5 and 15 kg 15% by weight aqueous NH 3 solution are added to 35 kg of the TiO 2 anatase mentioned in claim 1 with a BET surface of 280 m 2 /g.

The thinly liquid paste is kneaded for 2 to 4 hours at to a residual moisture content of 5 to 10% by weight. The dry powder is then precalcined for 2 hours at 700"C.

kg f-lly deionized water, 75 kg 15% by weight NH 3 solution and 2.0 kg monoethanolamine are added to the precalcined mixture, followed by further processing as in Examples 1 to 9. The final catalyst paste is extruded to honeycombs as in Examples 14 to 17.

SIn Examples 19 to 21, zirconium dioxide was replaced by ammonium paratungstate or phosphorus pentoxide and, in Example 20, V 2 0 5 was replaced by iron(III) oxide, as shown in Table 4.

S

e* o S S S r o *0 see *06 0 *0 00* iq 89 116 KY Table 4 Example Comp. A Comp. B 1 Ratio by weight Comp. B 2 Proportion of B 2 oxide A oxide/B 1 oxide in g/100 g A-B 1 mixed oxide 18 Anatase ZrO 2 9 1 V 2 0 5 19 Anatase APW 9 1 V 2 0 5 Anatase APW 9 1 Fe 2

O

3 21 Anatase P 2 0 5 9.5 0.5 V 2 0 5

I

i I i- 89 116 KY Examples 22 to 26 422 g ammonium-2-hydrogen-12-vanadophosphate and 28 litres deionized water are added to 35 kg of the TiO 2 anatase mentioned in claim 1 with a BET surface of 98 m 2 /g.

The paste is intensively kneaded at temperatures of to 70-C, 670 g SiO 2 2.5 kg glass fibres (length 1 to 8 mm) and 6.0 kg alkali-free clay being additionally introduced.

In addition, 450 g polyethylene oxide, 900 g carboxymethyl cellulose, 250 g lactic acid and 15 litres deionized water are added to establish the necessary plasticity.

The mixture is kneaded for 5 to 7 hours to a homogeneous kneaded paste which is then processed as in Examples 1 e to 9 to honeycomb monoliths.

S In Examples 23 to 26, the ammonium-2-hydroxy-12vanadophosphate was replaced by heteropoly acids, as shown in Table Table *00

S

S. B Example Comp. A Comp. B 1

B

2 Ratio by weight A oxide/B 2 oxide 22 Anatase (NH 4 5

H

2

[P(V

2 0 36 9.99 0.01 23 Anatase (NH) 8 [V 6 W0 3 7 9.9 0.1 24 Anatase H 4 [P(Mo 1

VO

40 9.99 0.01 Anatase H 6 [P(MoV 3

O

40 9.99 0.01 26 Anatase (NH 4 6 H[P(Mon 1 Cu0 40 9.99 :0.01 Examples 27 to 31 4.3 kg ammonium paratungstate, 22 litres deionized water, 7.5 kg 15% by weight aqueous NH 3 solution and 1.8 kg monoethanolamine are added to 35 kg of the TiO 2 anatase

I

21 89 116 KY mentioned in Example 1 with a BET surface of 98 m 2 As in Examples 1 to 9, the paste is provided with additives (plasticizers, supporting materials, etc.), intensively kneaded (2 to 7 hours at 60 to 90*C) and extruded to honeycomb monoliths which, in this case, count as catalyst precursors. The monoliths are dried and calcined as in Examples 1 to 9 and, after cooling (ac in claim 1.0 g vanadium pentoxide per 100 g titanium dioxide/tungsten oxide mixture is applied by impregnation with a solution of ammonium-2-hydrogen-±2-vanadophosphate in a quantity of water correspondingto the water absorption capacity of the o* yas mentioned in claim- f wing honeycomb monolith. The monoliths are dried at 150°C Zla air flo-ws through and are subsequently conditioned for 2 hours at 400°C.

In Examples 28 to 31, the ammonium paratungstate and ammonium-2-hydrogen-12-vanadophosphate are respectively replaced by the quantities shown in Table 6 of ammonium metatungstate, yttrium oxide, zirconium dioxide or silicon dioxide and V 2 0O (in the form of aqueous solutions of 20 vanadium oxalate), ammonium-6-tungstato-6-vanadate or 11molybdo-l-vanadophosphoric acid.

*9 0 9 00 0** ~0* *0 0 0 0** *0 0 22 89 116 KY Table 6 Example Comp. A Comp. B 1 Ratio by weight Comp. B 2 Proportion of B 2 oxide A oxide/B 1 oxide i n g/100 g A-B 1 mixed oxide 27 Anatase APW 9 1 (NH 4 )AHI[P (V 1 2 0 3 6 1 28 Anatase AMW 9 1 V 2

(C

2 0 4 5 29 Anatase Y 2 0 3 9.8 0.2 V 2

(C

2 0 4 5 Anatase Zr0 2 9 1 (NH 4 8 [1V 6

W

6 0 3 7 31 Anatase Si0 2 9 1 H 4 [IP (Mol 1 V0 4 0 23 89 116 KY Testing of the catalysts produced The catalysts prepared in accordance with Examples 1 to 31 were tested in the exhaust gas of an oil-burning plant which was adjusted to meet the following test conditions by the introduction of additional pollutants (NOx and SOz) and ammonia required for nitrogen oxide reduction.

Test conditions: Exhaust gas composition: NOx 800 ppA NH3 800 ppm SO2 500 ppm 02 5.0 by vol.

HzO 11.0 by vol.

CO

2 12.0 by vol.

N

2 balance ee*15 The catalyst tests were carried out at a temperature in the range from 250 to 500°C and at a space velocity of 20,000 h Selected results of the measurements and longterm tests in dry coal-burning plants under the conditions 20 already described are shown in the form of graphs in Figures 1, 2 and 3. The basic measured data are shown in Tables 7 and 8.

66* 0.

0* 0 i .SO• 0* S 0 0 000 OSO S S S S S S S 0 *5 S S S *4 SO S S S S S S S S *5 S S 5 50 S SO@**S 0* S S 89 116 KY Table 7* ,ExampleI No.

1 6 10 13 1A 18 23 27 Comparison T Example 250 46.0 43.8 39.5 40.5 45.2 44.2 42.5 45.8 34.5 290 63.1 60.1 57.5 58.5 62.7 60.5 67.6 62.7 52.0 320 75.7 72.2 69.4 71.1 73.5 72.5 70.7 74.9 63.9 360 86.0 84.1 81.3 82.6 84.0 83.0 81.1 85.4 74.7 400 93.4 90.6 87.0 88.2 91.5 89.9 87.5 92.7 81.8 450 94.3 92.3 87.8 89.0 92.4 91.1 88.4 94.0 83.1 500 90.4 86.6 80.8 81.5 87.5 86.6 83.3 88.5 76.0 v aIu e s *The figures shown represent NO xconversions (nNO in percent based on NO concentration

X

x the starting a I7 3

S

0 S S 0* *550

S

005*

S

59* Sd SO S

S

*5S*

S

*55* 0*5S S S S *5 4* S S

OS

*5000e

S

a. 54 89 116 KY Table 8* Dry coal-burning plant (T=45 0

-C)

t[h] Examples Comparison 1 6 13 Example Zero measurement 95 92 89 83 500 91.5 86 84.5 75.5 1000 89.5 85 84 73.5 2000 88 85 83.5 73 3000 88 84.5 83.5 72.5 4000 87.5 84.5 83.5 f 71.5 va Lues *The 44ae s shown represent NO xconversions (iNo in xx percent, based on the starting NO xconcentration

Claims

1. A catalyst for the selective reduction of nitrogen oxides with ammonia containing the following components: A) titanium oxide Bi) at least one oxide of tungsten, silicon, boron, aluminium, phosphorus, zirconium, barium, yttrium, lanthanum, cerium and B 2 at least one oxide of vanadium, niobium, molybdenum, iron, copper, I with an atomic ratio between the elements of components A) 10 and B) of 1 0.001 to 1 and preferably 1 0.002 to 0.4, obtainable by intensively kneading component A) in the form of a reactive high-surface titanium oxide having a BET surface of 40 to 500, preferably 50 to 300 and more prefer- ably 75 to 150 m 2 which is completely or predominantly present in the anatase modification, together with com- ponents Bi) and B 2 preferably their precursors, with addition of the additives typically used for the compres- sion moulding or extrusion of ceramic pastes, moistening agents, supporting substances, binders, moulding aids and, optionally, air-entraining agents, to form a homogeneous kneaded paste, extruding the kneaded paste to mouldings, drying the mouldings with a gradual increase in temperature to at most 60*C and then calcining them with a stepwise increase in temperature in ambient air at final tempera- tures in the range from 300 to 800*C.

2. A catalyst as claimed in claim 1, obtainable by using hydroxides, oxides, salts or heteropoly acids or salts thereof, preferably ammonium salts, as starting material for components Bi) and B 2

3. A catalyst as claimed in claim 1 or 2, obtainable by i Il 7 89 116 KY 0 S Si. I SC mixing component A) and component Bi) in the kneader and subjecting the resulting mixture to dry preliminary knead- ing at pH 7 to 11 -a4 preferably at pH 8 to 101 to a residu- al moisture content of 3 to 12% by weight -a-ld-preferably of r-em 5 to 10% by weight before component B 2 is added.

4. A catalyst as claimed in claim 3, obtainable by precalcining the dry-prekneaded mixture of components A) and Bi) at temperatures of 400 to 700"C before component B 2 is added.

5. A catalyst as claimed in claims 1 to 3, obtainable by precalcining the paste consisting of components Bz) and B 2 at 300 to 800'C and preferably at 400 to 700°C before it is kneaded to a homogeneous kneaded paste.

6. A catalyst as claimed in claims 1 to 5, characterized in that components and B 2 are used in the form of a heteropoly acid or one of its salts, preferably the ammon- ium salts, the metals of groups and B 2 present in the heteropoly acid being present in an atomic ratio of 12 1 to 1 12.

7. A catalsyt as claimed in claim 1 or 2, obtainable by leaving the starting material for component B 2 out of the kneading process and applying it by impregnation in the form of a salt or a heteropoly acid or one of its salts, preferably the ammonium salts, in aqueous solution to the preferably calcined catalyst precursor consisting of components A) and B 1

8. A catalyst for the selective reduction of nitrogen oxides with ammonia substantially as hereinbefore described with reference to any one of the Examples excluding the comparative examples.

9. A process for the selective reduction of nitrogen oxides with ammonia, which process comprises contacting nitrogen oxides with ammonia in the presence of a catalyst as defined in any one of claims 1 to 6. DATED this TWELFTH day of FEBRUARY 1990 Degussa Aktiengesellschaft Patent Attorneys for the Applicant SPRUSON FERGUSON 5.55.5 S S. S 5