AU700120B2

AU700120B2 - Catalytic compositions for the reduction of nitrogen oxides, based on tantalum, vanadium, niobium, copper or antimony

Info

Publication number: AU700120B2
Application number: AU36567/95A
Authority: AU
Inventors: Philippe Barthe; Pierre Macaudiere; Thierry Seguelong
Original assignee: Rhone Poulenc Chimie SA
Current assignee: Rhodia Chimie SAS
Priority date: 1994-10-13
Filing date: 1995-10-06
Publication date: 1998-12-24
Anticipated expiration: 2015-10-06
Also published as: BR9509354A; FI971497A; WO1996011740A1; FI971497A0; CA2202185A1; MX9702654A; CN1171062A; JPH10502020A; AU3656795A; EP0785820A1; KR970706888A

Description

Nox.

According to one aspect, the present invention consists in a process for treating gases with a high oxygen content and which continuously have an excess of oxygen related to the stoichiometric value k 1, in order to reduce nitrogen oxide emissions, wherein a catalytic composition based on antimony is used.

According to another aspect, the present invention consists in a process according to the previous aspect wherein a combination of antimony with at least one element chosen from the group consisting of zinc and elements of groups IllIb, IVb and Vb of the Periodic Table is used.

10 According to another aspect, the present invention consists in a process for treating gases with a high oxygen content and which continuously have an excess of oxygen %99 9 related to the stoichiometric value k 1, in order to reduce nitrogen oxide emissions, 99 wherein a catalytic composition consisting essentially of tantalum is used.

*According to another aspect, the present invention consists in a process for treating 99 15 gases with a high oxygen content and which continuously have an excess of oxygen related to the stoichiometric metric value 1, in order to reduce nitrogen oxide emissions, wherein a catalytic composition consisting essentially of at least one element selected from a first group including tantalum, vanadium and niobium and at least one other element selected from a second group including zinc and the elements of groups IIlb, IVb and Vb of the Periodic Table is used.

According to another aspect, the present invention consists in a process for treating gases with a high oxygen content and which continuously have an excess of oxygen related to the stoichiometric value k 1, in order to reduce nitrogen oxide emissions, in which the gases are treated either in the presence of a reducing agent 2a chosen from among a hydrocarbon or organic compound containing oxygen, or in the absence of a reducing agent, wherein a catalytic composition based on at least one element selected from the group including tantalum, vanadium, niobium and antimony is used.

The present invention provides, as a first embodiment, a catalytic composition for reducing the content of nitrogen oxides in a gas having a high oxygen content, which is based on at least one element selected from tantalum, vanadium, niobium and antimony.

The present invention provides, as a second embodiment, a catalytic composition 10 which is based on at least one element selected from tantalum, vanadium, niobium and antimony and at least one other element from copper, silver and gold.

The present invention provides, as a third embodiment, a catalytic composition S•which is based on at least one element selected from tantalum, vanadium, niobium, 9. "•antimony and copper, and on at least one other element selected from zinc and the s15 elements of groups IIIb, IVb and Vb of the Periodic Table.

999999 oo The present invention provides, as a fourth embodiment, a catalytic composition which comprises copper and at least one other element selected from group Via of the Periodic Table.

The compositions of the invention have an action in the reduction of the emissions of nitrogen oxides either in the treatment of gases or in the presence or absence of a hydrocarbon and/or of an organic compound containing oxygen. In some cases, these compositions are effective at a low temperature.

I

3 Other characteristics, details and advantages of the invention will become even more fully apparent on reading the description which follows, as well as the various concrete but non-limiting examples intended to illustrate it.

The Periodic Table of the elements which is referred to in the description is that published in the supplement to the Bulletin de la Soci6t6 Chimique de France No. 1 (January 1966).

As mentioned above and according to a first embodiment of the invention, the catalytic composition comprises at least one element chosen from tantalum, vanadium, niobium and antimony.

According to the second embodiment of the invention, the catalytic composition comprises two categories of elements. It comprises, in effect, at least one element chosen from a first group consisting of tantalum, vanadium, niobium and antimony. It also comprises a second element chosen from a second group consisting of copper, silver and gold.

According to the third embodiment of the invention, the catalytic composition comprises a further two categories of elements. It comprises firstly at least one element chosen from a first group consisting of tantalum, vanadium, niobium, antimony and copper, and at least one other element chosen from a second group comprising zinc and the elements of groups IIIb, IVb and Vb of the Periodic Table.

As regards the elements of group IIIb, gallium and indium will be used more particularly.

Tin will be mentioned in particular for group IVb I I 4 and antimony and bismuth will be mentioned for group Vb.

The compositions according to the second embodiment and those of the third embodiment based on tantalum, vanadium, niobium and antimony have the advantage of being effective at a low temperature. Thus, it has been possible to demonstrate an activity of these compositions at temperatures as low as 300 0 C or, more particularly, as low as 200 0

C.

According to the fourth embodiment of the invention, the composition comprises copper and at least one other element chosen from group VIa of the Periodic Table.

Elements of group Via which may be mentioned more particularly are molybdenum and tungsten.

According to a particular variant, the compositions of the invention may also comprise a support.

Any support usually used in the field of catalysis may be used as support, for example ZrO,, A1 2 0 3 TiO 2 or SiO,, lanthanide oxides such as CeO 2 it being optionally possible for these supports to be doped, or alternatively spinel-type oxides, zeolites, silicates, crystalline silicoaluminium phosphates or crystalline aluminium phosphates, it being possible for these silicates or phosphates to comprise metal substituents such as, for example, titanium, iron, magnesium, zinc, manganese, cobalt, gallium, lanthanum, copper, molybdenum, chromium, germanium or boron.

A1 2 0 3 TiO 2 ZrO,, SiO, and spinels such as, for example, MgAl,04 may be used more particularly as support.

According to a particular embodiment of the invention, cerium oxide may be used as support.

For alumina, there may in particular be mentioned 5 the aluminas obtained by rapid dehydration of at least one aluminium hydroxide such as bayerite, hydragillite or gibbsite, nordstrandite and/or of at least one aluminium oxyhydroxide such as boehmite, pseudoboehmite or diaspore.

According to a particular variant, a stabilized alumina may be used. Rare-earth metals, barium, silicon and zirconium may be mentioned as stabilizing element. Lanthanum or a lanthanum-neodymium mixture may be mentioned more particularly as rare-earth metal.

For titanium dioxide, it is also possible to use an oxide stabilized, for example, by a rare-earth metal such as lanthanum, or by barium, strontium, phosphorus, silicon, zirconium or aluminium.

The elements described above which constitute the composition may be present therein in various types of phases, generally in the form of oxides or mixed oxides, it being possible for these mixed oxides to contain certain elements of the support in the case of supported compositions.

The amounts and, in particular, the respective amounts of the elements which constitute the compositions of the invention may vary within wide proportions. The invention thus applies to compositions in which tantalum, vanadium, niobium, antimony and copper are in majority in atomic percentage terms relative to the other elements, such as to those in which these other elements are in majority. In the case of supported compositions, this amount is generally between 1 and 50% and more particularly, especially in the case of copper, between 10 and 50%, expressed as an atomic 6 content of element relative to the sum of elemental atoms and moles of support.

The compositions of the invention may, lastly, comprise precious metals of the type used conventionally in catalysis and, in particular, in vehicle postcombustion catalysis.

Examples of metals which may be mentioned are platinum, palladium and rhodium, palladium being preferred.

Particular embodiments of the invention which will lastly be mentioned are the compositions which comprise copper, at least one other element selected from groups Va, IIIb, IVb and Vb of the Periodic Table and a support made of cerium oxide.

Another particular embodiment which may be mentioned is the compositions essentially comprising the elements mentioned above, that is to say the compositions in which only these elements have a catalytic action, possibly in combination with precious metals of the type described above.

The catalytic compositions of the invention may be prepared by any process which makes it possible to obtain an intimate mixture of the constituents of the compositions of the invention. Various processes may be mentioned by way of example.

According to a first process, these compositions are obtained by grogging precursors of the elements and, if necessary, of the support.

These precursors are generally oxides, hydroxides, carbonates or oxalates. They are mixed together and ground and then optionally shaped under pressure, for example 7 pastilled. The mixture is then calcined.

According to a second process, a solution or a slip of salts of the elements and, where appropriate, of the support is first formed.

Salts which may be chosen are salts of inorganic acids such as nitrates, sulphates or chlorides.

It is also possible to use salts of organic acids and, in particular, salts of saturated aliphatic carboxylic acids or salts of hydroxycarboxylic acids. Examples which may be mentioned are the formates, acetates, propionates, oxalates and citrates.

Next, either the solution or the slip is precipitated by addition of a precipitating agent in the presence, where appropriate, of the support, or it is atomized before calcination.

In the latter case, a sol may be used instead of a salt of the elements.

According to another process and in the case of supported compositions, the support is impregnated with a solution or a sol of the abovementioned elements. After impregnation, the support is optionally dried and it is then calcined. The solutions which may be used are the same as those which have been described above. For tantalum and niobium, alcoholic solutions of these elements are more generally used, in particular chloride solutions.

For the preparation by impregnation of a composition according to the second or third embodiment of the invention, either a coimpregnation of the elements of the various groups may be carried out or the process may be performed in two 8 stages.

In this case, the support is first impregnated with a solution of one of the two groups of elements. The support is optionally dried. In a second stage, the support is impregnated with a solution of an element from the other group. The support thus impregnated is optionally dried and is calcined.

Dry impregnation is more particularly used. Dry impregnation consists in adding a volume of an aqueous solution of the element, which is equal to the pore volume of the solid to be impregnated, to the product to be impregnated.

The compositions of the invention may be in various forms, such as granules, beads, cylinders or honeycombs of variable sizes.

The invention also provides a catalytic system comprising a composition as defined above, for example a system comprising a coating of known composition, in particular a base of a refractory oxide (wash coat) based on these compositions, on a substrate of the metal monolith or ceramic monolith type, for example.

The systems are mounted in a known way in catalytic devices such as vehicle exhaust pots in the case of application to the treatment of exhaust gases.

The invention also provides the use of a composition or catalytic system as defined above in the manufacture of a catalyst or catalytic device for motor vehicle postcombustion.

The gases which may be treated by the compositions 9 of the present invention are, for example, those exiting gas turbines, central heating boilers or internal combustion engines, in particular diesel engines or engines which run on a lean mixture.

The invention applies to the treatment of gases which have a high oxygen content and which contain nitrogen oxides, for the purpose of reducing the emissions of these oxides. The expression "gas having a high oxygen content" means gases which continuously have an excess of oxygen relative to the stoichiometric value X 1. The value X is correlated to the air:fuel ratio in a manner which is known per se, in particular in the field of internal combustion engines. In other terms, the invention applies to the treatment of gases obtained from systems of the type described in the above paragraph and working continuously under conditions such that X is always strictly greater than 1. The invention also applies to the treatment of gases, such as exhaust gases, which have an oxygen content (expressed by volume) of at least more particularly of at least 10%, it being possible for this content to be, for example, between and The gases may contain a reducing agent or may be treated in the presence of a reducing agent such as a hydrocarbon and, in such a case, one of the reactions which it is sought to catalyse is the reaction HC (hydrocarbon)

NO,.

The hydrocarbons which may be used as reducing agent for removal of the NO, are, in particular, gases or liquids from the families of saturated carbides, ethylenic carbides, 10 acetylenic carbides, aromatic carbides and hydrocarbons from petroleum fractions such as, for example, methane, ethane, propane, butane, pentane, hexane, ethylene, propylene, acetylene, butadiene, benzene, toluene, xylene, kerosene and gas oil.

The gases may also contain, as reducing agent, organic compounds containing oxygen, or they may be treated in the presence of these compounds. These compounds may in particular be alcohols of the saturated alcohol type, for example, such as methanol, ethanol or propanol; ethers such as methyl ether or ethyl ether; esters such as methyl acetate, and ketones.

It should, however, be noted that, according to an advantageous characteristic of the invention, the treatment process may be performed on a gas without the presence of a reducing agent. This applies most particularly in the case of compositions which comprise copper and at least one other element chosen from groups Va, IIIb, IVb and Vb of the Periodic Table and a support made of cerium oxide.

I

11 Examples will now be given.

In the examples given below, and except where otherwise mentioned, the compositions are tested as follows in order to evaluate their catalytic performance.

1.5 g of the catalyst powder are loaded into a quartz reactor.

The reaction mixture entering the reactor has the following composition (by volume): NO 300 vpm

C

3 H 3 00 vpm 02

CO

2

H

2 0 N, qs 100% The overall flow rate is 10 NL/h.

The STY is of the order of 10,000 h-.

The NO and NO. (NO, NO NO 2 signals are continuously recorded, as is the temperature in the reactor.

The NO and NO, signals are given by an Ecophysics

NO,

analyzer, based on the principle of chemiluminescence: this gives the values of NO and NO,.

The catalytic activity is measured from the NO and NO, signals as a function of the temperature during a programmed temperature rise from 20 to 700 0 C at a rate of 3.75°C/min and from the following relationships: The degree of conversion into NO (DNO) in which is given by: D(NO) 100(NO*-NO)/NO 0 where NO is the signal for NO at time t 0, which corresponds to the signal for NO obtained 12 with the reaction mixture when the catalytic reactor is bypassed, and NO is the signal for NO at time t.

The overall degree of conversion of the NO, (DNO,) in which is given by:

D(NO

x 100(NO,°-NO,)/NO,o where NO," is the signal for NO, at time t 0, which corresponds to the signal for NO, obtained with the reaction mixture when the catalytic reactor is bypassed, and NO. is the signal for NO, at time t.

The degree of conversion of NO, into N 2 0 (DNO) in which is given by:

D(N

2 0) 100(N 2 0-N 2 where N 2 0° is the signal for N 2 O at time t 0, which corresponds to the signal for N 2 0 obtained with the reaction mixture when the catalytic reactor is bypassed, and N 2 0 is the signal for N 2 0 at time t.

Lastly, the term specific surface refers to the B.E.T. specific surface determined by adsorption of nitrogen in accordance with ASTM Standard D 3663-78, established using the Brunauer-Emmett-Teller method described in "The Journal of the American Society, 60, 309 (1938)".

13 EXAMPLE 1 This example relates to compositions based on niobium.

1) Synthesis of the catalysts Copper nitrate (Cu(NO 3 2 3H 2 O0), tin chloride (SnC1 4 gallium nitrate (Ga(N0 3 3 solution, indium nitrate (In(NO 3 3 solution, zinc nitrate (Zn(N0 3 solution and niobium chloride (NbCl s are used as starting materials.

The support used is undoped alumina, calcined at 1090°C for 8 h in order to bring its specific surface to 28 m 2 /g before deposition of the active elements.

The atomic content of active element is calculated as follows: [A120 3 0.10 where X Cu, Zn, Ga, Sn or In, where represents the number of moles of the species considered. The same content of niobium and of second doping element (5 atom of each) was deposited on the support, i.e.: [XI [A1 2 0 3 0.05 [A1 2 0 3 0.05 where X Cu, Zn, Ga, Sn or In.

The following procedure is used in order to prepare the catalytic compositions: Dry impregnation of the first element using an alcoholic solution of niobium resulting from the dissolution of NbCl 5 by anhydrous ethanol, the alumina having a pore volume of 0.70 cm 3 /g.

Drying in the oven (110*C, 2 h).

14 Dry impregnation of the second element X (X Cu, Zn, Ga, Sn, In), in all cases in the form of an aqueous solution.

Drying in the oven (110 0 C, 2h).

Calcination in air at 750 or 950 0 C for 2 h, rise of 5 0 C/min.

The products obtained have the following characteristics: Example 1.1: calcination at 750 0

C,

Example 1.2: calcination at 950 0

C,

Example 1.3: calcination at 750 0

C,

Example 1.4: calcination at 750 0

C,

Example 1.5: calcination at 750 0

C,

[Nb] 5 atom and SBET 19.5 m 2 /g.

[Nb] 5 atom and SBET 24.5 m 2 /g.

[Nb] 5 atom and SBET 23.0 m 2 /g.

[Nb] 5 atom and SBET 24.5 m 2 /g.

[Nb] 5 atom and SBET 21.5 m 2 /g.

[Cu] 5 atom [Zn] 5 atom [Ga] 5 atom [Sn] 5 atom [In] 5 atom 2) The catalytic performance results are given in Tables I to V below: 15 Table I Example 1.1 Temperatures DNO

DNO.

150 0 0 200 2.4 1.8 250 15.1 13.4 300 21.4 13 350 43.3 16.5 400 49.4 15.2 450 41.6 7.9 500 32.9 0.7 Table II Example 1. 2 Temperatures DNO

DNOX

150 0 0 200 0 0.8 250 0.1 4.2 300 3.1 7.4 350 7.7 11.6 400 9.4 14.6 450 11.6 16.3 500 12.6 17.7 550 11.6 16.5 600 8.2 12.9 650 7.5 8.8 700 5.8 5.7 16 Table III Example 1.3 Temperatures DNO DNO.

150 0 0 200 0 1 250 2.5 4.2 300 9.1 11.2 350 15 18.1 400 23.4 26.1 450 31.7 34.9 500 35 38.8 550 29.5 32.6 600 13.6 14.9 650 6.6 5.3 Table IV Example 1. 4 Temperatures DNO DNOx 150 0 0 200 1.4 2.1 250 4.7 5.9 300 10.7 12.2 350 17 18.4 400 25.2 26.6 450 30.4 32.9 500 27 29.7 550 18.6 20.9 600 12.6 11.8 650 9.3 6.2 700 11.- 9 Table V 17 Example Temperatures DNO

DNO,

250 0 0 300 4.7 5.1 350 21.8 22.7 400 23.5 27.9 450 35.4 37.2 500 29.9 33.5 550 21.8 22 600 12.9 9.8 650 7.4 3.4 700 10.8 1 Examples 1.3, 1.4 and 1.5 show a very good level of activity, for the specific surface considered 25 m 2 with a maximum conversion of NO, of greater than 30% at about 500 0 C. Furthermore, the temperature range for NO, conversion is very wide (between 350*C and 600 0 C approximately for an NO. conversion of greater than A reaction initiation temperature of below 200 0 C for Examples 1.3 and 1.4 should also be noted, this being very advantageous for a diesel engine.

In the case of Example 1.1, the conversion takes place over a wide temperature range of between 2500C and 400 0 C approximately. Furthermore, the reaction initiation temperature for NO, conversion is also below 200 0

C.

Example 1.2 gives results which are intermediate between the above examples.

18 EXAMPLE 2 This example relates to compositions based on tantalum.

1) Synthesis of the catalysts The same starting materials as those of the above example are used, along with tantalum chloride (TaCl s in place of niobium chloride.

The tantalum content and the content of other elements are identical to those of Example 1, the catalysts being prepared according to the same procedure.

The products obtained have the following characteristics: Example 2.1 [Ta] 5 atom and [Cu] 5 atom calcination at 750 0 C, SBET 20.0 m'/g.

Example 2.2 [Ta] 5 atom and [Zn] atom calcination at 950°C, SBET 22.5 m 2 /g.

Example 2.3 [Ta] 5 atom and [Ga] atom calcination at 950C, SBET 22.5 m 2 /g.

Example 2.4 [Ta] 5 atom and [Sn] atom calcination at 950 0 C, SBET 22.5 m 2 /g.

Example 2.5 [Ta] 5 atom and [In] atom calcination at 950°C, SBET 20.5 m 2 /g.

2) The catalytic performance results are given in Tables VI to X below.

19 Table VI Example 2.1 Temperatures DNO

DNOX

250 0 0.2 300 5 2 350 10.1 400 27.7 9.2 450 37.6 11.8 500 31.6 7.6 550 24.7 3.6 600 21.7 1.3 650 18.8 0 Table VII Example 2.2 Temperatures DNO

DNO

x 300 0 0 350 3 3.1 400 6.7 8.1 450 11.2 12.5 500 11.2 18.9 550 13.8 21 600 7.9 12.2 650 7.9 5.2 700 3.3 1.2 20 Table VIII Example 2.3 Temperatures DNO

DNO.

300 0 0 350 2.8 5.8 400 10.7 12.8 450 24.1 26.1 500 39.9 42.2 550 43.7 45.4 600 19.5 19.2 650 12.8 7.2 700 10.1 3.2 Table IX Example 2.4 Temperatures DNO

DNO.

250 0 0 300 4.7 4.9 350 21.9 23.1 400 28.2 32.9 450 30 36.2 500 25 32.5 550 18.6 21 600 8.9 650 4.7 2 21 Table X Example Temperatures DNO

DNO

X

250 0 0 300 6 6.4 350 26.3 30.8 400 30.3 34.6 450 32.2 36.3 500 32.1 33.8 550 22.3 23.8 600 11.1 11.7 650 4.8 3.8 Examples 2.3, 2.4 and 2.5 show a very good level of activity, for the specific surface considered 25 m 2 with a maximum of NO, conversion of greater than 30% at about 500 0 C. Furthermore, for Examples 2.4 and 2.5, the temperature range for NO x conversion is very wide, between 350 0 C and 550°C approximately, for an NO x conversion of greater than EXAMPLE 3 This example relates to a composition based on vanadium.

1) Synthesis of the catalyst Copper nitrate (Cu(NO 3 2 ,3H20) and sodium orthovanadate (Na 3

VO

4 in aqueous solution are used.

The support used is the same as that for Example 1.

The vanadium and copper contents are identical to those of Example 1, as is the procedure.

22 The product obtained has the following characteristics: Example 3.1 5 atom and [Cu] 5 atom calcination at 750C, SBET 14.0 m 2 /g.

2) The catalytic performance results are featured in Table XI. These results show: a good level of activity, for the specific surface considered 20 m 2 with a maximum of NO, conversion of the order of 65% at about 500 0

C.

a relatively wide range of temperature of activity, of about 100°C, between 450 0 C and 550 0 C in which the NO x conversion remains greater than 20 a reaction initiation temperature for NO x conversion of below 200 0

C.

Table XI Example 3.1 Temperatures DNO

DNO.

100 0 0 150 0 0.2 200 2.3 4.2 250 3.8 6.7 300 3.5 6.6 350 0.4 4.9 400 0 2.4 450 24.3 25.8 500 66 66.3 550 46.4 48.3 600 0 0 23 EXAMPLE 4 This example illustrates compositions based on a single active element.

These compositions are prepared with the same support as in Example 1 and, for niobium and tantalum, the same precursors as in Examples 1 and 2. For antimony, the precursor is antimony tartrate; for vanadium it is ammonium vanadate. The products obtained have the following characteristics: Example 4.1 [Sb] 5% calcination at 950 0 C, 2 h Example 4.2 [Nb] 5% calcination at 950 0 C, 2 h Example 4.3 [Ta] 5% calcination at 950°C, 2 h Example 4.4 5% calcination at 750C, 2 h The catalytic performance results are given in Tables XII to XV below.

24 Table XII Example 4.1 Temperatures DNO

DNO,

200 0 0 250 1.5 0 300 6.9 0 350 7.5 0 400 16.5 4.6 450 28.7 21.3 500 23.7 18 550 15.8 8.3 600 12.9 650 14.6 2.2 700 17.3 1 Example 4. 2 Table XIII Temperatures DNO DNO, 200 0 0 250 1 3.2 300 4.2 6.8 350 5.3 8.3 400 9.8 11.1 450 23.2 13.8 500 23.7 9.9 550 17.2 5.6 600 13.6 650 15.7 2 700 13.6 1.2 25 Table XIV Example 4.3 Temperatures DNO

DNO,

300 0 0 350 0 3 400 3.7 7.7 450 10.4 14.5 500 22.9 26.4 550 25 29.8 600 19.2 19.2 650 14 9.7 700 9.7 4.9 Table XV Example 4.4 Temperatures DNO DNO, 200 2.5 0 250 10.5 6.8 300 12.2 8.9 350 9.2 5.6 400 6.5 3 450 7.8 1.6 500 11.7 2.2 550 15.6 3 600 15 2.4 650 14.8 1.4 700 14.4 0.9 EXAMPLE This example illustrates a composition based on antimony and copper on a titanium support. The product is prepared in the same way as in Example 1.

26 For antimony, the precursor is the tartrate. The support is TiO 2 as a mixture of anatase and rutile with a surface of 60 The product obtained has the following characteristics: 7% and [Cu] 3% calcination at 750 0 C, 2h.

SBET 26 m 2 /g The catalytic performance results are given in Table XVI. 0.75 g of catalyst was loaded into the reactor in order to determine these performances.

Table XVI EXAMPLE 6 Temperatures DNO

DNO,

200 0 0 250 6 6 300 27.6 25.7 350 33.7 27.8 400 25.6 14.4 450 27.6 9.1 500 32.1 8.6 550 33.4 7.6 600 31.4 6.6 650 28.5 4.7 700 26.6 4.7 A composition based on niobium and gallium is prepared as in Example 1.

The support used is an alumina.

The product obtained has the following characteristics: [Nb] 20% and [Ga] 20% calcination at 27 750°C, 2h. SBET 118 m 2 /g.

The test was performed with an STY of 100,000 h- 1 and 150 mg of product.

The results are given in Table XVII.

Table XVII EXAMPLE 7 Temperatures DNO DNO, 200 0 0 250 0.5 300 2.4 350 3.1 2.4 400 6.1 5.6 450 14.1 13.3 500 30.6 550 50.6 49.5 600 61.7 49 650 42.2 28.7 700 20.1 10.9 This example relates to compositions based on copper.

1) Synthesis of the catalysts Copper nitrate (Cu(NO 3 2 ,3H 2 gallium nitrate (Ga(NO 3 3 solution, indium nitrate (In(NO 3 3 solution, tin chloride (SnCl 4 zinc nitrate (Zn(N0 3 solution, bismuth nitrate solution, ammonium metatungstate

((NH

4 6

H

2 W20O4) and ammonium heptamolybdate ((NH 4 MoO, 24 are used as starting materials.

The support used is undoped alumina, calcined at 1080 0 C for 8 h in order to bring its specific 28 surface to 37 m 2 /g before deposition of the active elements.

The atomic content of active element is calculated as follows: [A1,0 3 0.10 where X Mo, Ga, Sn, Zn, Bi, In and W.

where represents the number of moles in the species considered.

In order to prepare the catalytic compositions, the procedure is as follows: Dry impregnation of copper, the alumina having a pore volume of 0.70 cm'/g.

Drying in the oven (110 0 C, 2 h).

Dry impregnation of the second element X.

Drying in the oven (110 0 C, 2h).

Calcination in air at 750C for 2 h, a rise of 5 0 C/min.

The products obtained have the following characteristics: Example 7.1: [Cu] 5 atom and [Ga] calcination at 750 0 C, SBET 23 m'/g.

Example 7.2: [Cu] 7 atom and [Mo] calcination at 750 0 C, SBET 18.5 m 2 /g.

Example 7.3: [Cu] 9 atom and [Mo] calcination at 750 0 C, SBET 18.5 m 2 /g.

Example 7.4: [Cu] 5 atom and [Sn] calcination at 750 0 C, SBET 18 m 2 /g.

Example 7.5: [Cu] 5 atom and [Zn] calcination at 750 0 C, SBET 23.5 m 2 /g.

5 atom 3 atom 1 atom 5 atom 5 atom 29 Example 7.6: (Cu] a 5 atom and [Bi] 5 atom %calcination at 7500C, SEET 18 m 2 /g.

Example 7.7: [Cu] 5 atom and [In] 5 atom %,calcination at 750 0 C, SEET 22 m 2 /g.

Example 7.8: [Cu] 5 atom and [WI atom in this case, the support was first dryimpregnated with ammonium metatungstate and, in a second stage, the impregnation with copper and calcination at 7500C were then performed, SEET 25.3 m 2 /g.

2) The catalytic performance results are given in Tables XVIII to XXV below.

30 Table XVIII Example 7.1 Temperatures DNO DNOX 250 0 0 300 19.4 14.5 350 29.6 23.9 400 32.2 15.4 450 40.1 10.1 500 37.4 8.3 550 31.8 4.9 600 27.5 2.7 650 24.7 1.6 Table XIX Example 7.2 Temperatures DNO DNO.

200 0 0.8 250 4.2 2.8 300 14.5 8.4 350 25 17 400 15.2 4.7 450 21.3 2.1 500 29.3 3.2 550 27.5 1.3 600 24.5 0 31 Table XX Example 7.3 Temperatures DKO

DNO.

200 0 0 250 1.1 1.2 300 7.7 7.6 350 21.1 19 400 15 10.8 450 18.3 7.1 25.5 8.7 550 25.2 6.8 600 23 5.4 650 21. 1 5.1 Table XXI Example 7.4 Temperatures- DNO

DNO.

200 0.8 0.7 250 1.2 1.2 300 11.3 350 11.3 4.9 400 34.5 450 44.3 11.6 500 37.3 7.1 550 31.3 600 27.9 1.9 650 26.8 0 32 Table XXII Example Temperatures DNO DNO.

250 0 0 300 8.5 3.9 350 23.8 17.7 400 26.3 13.8 450 35.1 3.7 500 33.6 2.6 550 29.1 600 25.9 0 Table XXIII Example 7.6 Temperatures DNO DNO.

300 0.3 0 350 20.5 16.2 400 30.6 16.4 450 25.1 0 Table XXIV Example 7.7 Temperatures DNO DNO.

250 0 0 300 5.8 350 24.4 23.1 400 37.4 18.7 450 37.5 7.6 500 32.5 6.2 550 25.9 4.4 600 21.9 2.6 650 18.5 0.9 33 Table XXV Example 7.8 Temperatures DNO nw EXAMPLE 8 200 0 0 250 6.3 6.3 300 19.9 19.9 350 35.6 36.6 400 19.7 17.4 450 21.2 9.3 500 23.2 6.4 550 20.8 4.6 600 17.1 1.8 650 15.1 0.7 700 13.2 0.3 This example relates to compositions based on copper and comprising a CeO, support.

The compositions are tested using 50 mg thereof in the form of powder of particle size 125-250 Am, diluted in 150 mg of SiC of the same particle size.

The total gas flow rate is 30 Nl/h. The STY is 500,000 h- 1 The composition of the gas mixture treated is that given above in the preamble of Example 1, with, in addition, a CO content of 350 vpm.

In certain cases, the gas mixture treated contains no hydrocarbon and then corresponds to the following composition: NO 300 vpm, 02 34 CO, 10%, H 2 0 10% and N 2 qs 100%.

1) Synthesis of the catalysts Copper nitrate (Cu(NO 3 2 3H 2 gallium nitrate (Ga(N0 3 solution, bismuth nitrate (Bi(N0 3 3 .5H 2 0), hexachloroplatinic acid (H 2 PtCl,), a niobium alkoxide and sol and a tin sol are used as starting materials.

The niobium alkoxide is obtained by dissolving niobium chloride in ethanolic medium at 70°C for 2 hours with stirring. The niobium sol is obtained by precipitating the niobium alkoxide in ammoniacal medium.

Tin sol is prepared by adding, volume for volume, a solution of NH 4 OH (1.70 mol/l) to a solution of tin chloride (SnC1 4 0.50 mol/l). After washing several times with an ammoniacal buffer at the precipitation pH (in the region of 8.7) in order to remove the chlorides, the precipitate is prepared by centrifugation and is resuspended in water in order to form a sol.

The support used is cerium oxide, CeO from Rh8ne-Poulenc. The atomic content of active element is relative to the number of moles of cerium oxide, i.e.: (Ce0 2 0.10 where X Sn, Nb, Ga or Bi, where represents the number of moles of the element considered, or: [Cu] 0.1 and [CeO,] 0.9.

35 The method of preparation is a dry impregnation, which is carried out under the same conditions as those of Example 1. The calcination is performed in air, at 750°C for 2 hours, with a rise of The products obtained have the following characteristics: Example 8.1 and 8.2: [Sn] 5 atom and [Cu] 5 atom SBET 63 m 2 /g.

Example 8.3 and 8.4: [Ga] 5 atom and [Cu] 5 atom SBET 60 m 2 /g.

Example 8.7: [Bi] 5 atom and [Cu] 5 atom SBET 31 m 2 /g.

Example 8.8: [Nb] 3 atom and [Cu] 7 atom SBET 63 m 2 For this example, the impregnation was made on a support doped with platinum, the amount of platinum in the composition being 2500 ppm. The niobium is introduced as the alkoxide.

Example 8.9: This example is performed with the composition of Example 8.8, but the catalyst was aged for 6 h at 750 0 C, at a gas flow rate of 100 N1 h' 1 and at 10% 02, 10% CO 2 and 10% For the other examples, the products were prepared by the atomization method. A slip is formed having a concentration of reactants, expressed as oxide, of 180 g/1. The niobium is introduced in the form of a sol. This slip is then atomized with a Buchi atomizer, with an inlet temperature of 220°C and an outlet temperature of 130 0 C. Calcination is carried out 36 as in the above examples.

Example 8.5: (Nb) 3 atom and [Cu] 7 atom %,SEET 84 m 2 Ig.

Example 8.6: [Nb] 7 atom and (Cu] 3 atom %,SBET 67 m 2 /g.

2) The catalytic performance results are given in Tables XXVI to XXXIV below.

Table XXVI Example 8.1 0 Temperature DNO ()DN 2 O DNO. (1 0

C)

200 0 0 0 250 2.7 0 300 4.7 0 3.9 350 8.6 0 6.2 400 20.3 0 13.9 450 23.9 0 17.5 500 24.6 0 18.2 550 21.7 0 15.6 0 600 17.3 0 12.1 650 14.5 0 8.7 700 13.1 0 1 7.6 37 Table XXVI Example 8.2 In this example, the gas mixture contains no reducing agent of the hydrocarbon or CO type.

Temperature DNO DNO DNO, 200 0.2 0 0 250 3.5 0 300 9.4 0 5.6 350 20.9 0 13.1 400 44 0 26.6 450 36.9 0 21.1 500 24.9 0 14.1 550 15.3 0 600 11.7 0 5.6 650 8.8 0 4.2 700 7.8 0 3.8 Examples 8.1 and 8.2 demonstrate that the Cu-Sn/CeO 2 compounds are active with respect to the reduction of NO, emissions, in the presence or absence of a reducing agent of the HC and/or CO type. It will be noted that the catalytic activity is both higher and obtained at a lower temperature in the absence of reducing agent of the HC and/or CO type in the reaction mixture.

38 Examp~le 8.3 In this example, the gas mixtur, contains no reducing agent of the hydrocarbon or CO type.

Temperature DNO ()DN 2 0 DM0, M%

(OC)

200 2.4 0 0.2 250 5.4 0 3.1 300 5 0 2 350 11.2 0 7.1 400 36.1 0 26.7 450 40 0 30.7 500 33.2 0 24.9 550 27.4 0 20.2 600 21.9 0 15.2 650 18.7 0 12.2 700 17.4 0 10.7 t 39 Table XXx Temperature DNO DNO DNO, 200 0 0 0 250 0 0 0 300 0 0 0 350 6.3 0 4 400 10.9 0 6.6 450 13.8 0 8.1 500 16.1 0 550 13.5 0 7.4 600 9.2 0 4.4 650 6.3 0 2.2 700 5.3 0 Examples 8.3 and 8.4 demonstrate that the Cu-Ga/CeO, compounds are active with respect to the reduction of NO, emissions, in the presence or absence of a reducing agent of the HC and/or CO type. It will be noted that the catalytic activity is both higher and obtained at a lower temperature in the absence of reducing agent of the HC and/or CO type in the reaction mixture.

40 Table XX Example- In this example, the gas mixture contains no reducing agent of the hydrocarbon or CO type.

Temperature DNO M%

DN

2 O

DNO,(%

(OC)

200 0 0 0 250 2.6 0 2.1 300 5.3 0 3.2 350 11.2 0 5.9 400 38.1 0 450 38.5 0 25.7 500 26.2 0 16 550 19.6 0 11.5 600 15.6 0 650 14.6 0 7.7 700 14.6 0 8.1 41 Table XXII Example 8.6 In this example, the gas mixture contains no reducing agent of the hydrocarbon or CO type.

Temperature DNO D D 0

C)

200 0 0 0 250 0.6 0 0.2 300 7 0 4 400 33.7 0 19.6 450 34.1 0 19.2 3 0 0 500 24.7 0 12.9 550 17 0 7.7 600 11.2 0 4.3 650 8.3 0 2.9 700 7 0 2.1 Examples 8.5 and 8.6 demonstrate that the systems of the Cu-Nb/CeO 2 type are active with respect to the reduction of NO, emissions in the absence of a reducing agent of the HC and/or CO type. The formulations with an excess of Cu relative to the Nb (expressed in atomic terms) are even more active under these conditions.

42 Tabe =1 ExamTple 8.7 In this example, the gas mixture contains no reducing agent of the hydrocarbon or CO type.

Temperature DNO ()DN 2 0 DNO.

(OC)

200 0 0 0 250 0 0 0 300 3 0 1.7 350 4.5 0 3.9 400 28.3 0 18.1 450 35.3 0 23.9 500 27 0 17.4 550 19 0 10.7 600 15.5 0 650 13.9 0 7.1 700 12.9 0 6.8 43 Table XXXIII Example 8.8 In this example, the gas mixture contains no reducing agent of the hydrocarbon or CO type.

Temperature DNM0 DN 2 O DM0 5 (1 0

C)

200 0.3 0 0.7 250 0 0 0 300 5.9 0 4 350 6.6 0 4.3 400 42.4 0 26.1 450 36.9 0 22.4 500 24.5 0 14.1 550 14.7 0 6.9 600 9.8 0 4.3 650 6.6 0 2.2 700 4.6 0 1.8 44 Table XXXIV Example 8.9 In this example, the gas mixture contains no reducing agent of the hydrocarbon or CO type.

Temperature DNO

DN

2 O DNO, 200 0.4 0 0.3 250 0 0 0 300 1.4 0 0.3 350 6.6 0 3.8 400 30.6 0 18.7 450 38.9 0 25.6 500 28.7 0 18.3 550 19.9 0 11.7 600 14.6 0 7.3 650 10.9 0 700 8.7 0 2.8 Comparison of the Examples 8.8 and 8.9 makes it possible to demonstrate the stability in the performance of the catalyst after a thermal ageing treatment for 6 hours at 750 C in the presence of water, CO, and oxygen in the gas mixture. Catalytic activity did not decrease as a result of this treatment.

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:- 1. Process for treating gases with a high oxygen content and which continuously have an excess of oxygen related to the stoichiometric value k 1, in order to reduce nitrogen oxide emissions, wherein a catalytic composition based on antimony is used.

2. A process according to claim 1 wherein a combination of antimony with at least one element chosen from the group consisting of zinc and elements of groups IIIb, IVb and Vb of the Periodic Table is used.

3. A process for treating gases with a high oxygen content and which continuously have an excess of oxygen related to the stoichiometric value k 1, in order to reduce 10 nitrogen oxide emissions, wherein a catalytic composition consisting essentially of tantalum is used.

4. Process for treating gases with a high oxygen content and which continuously have San excess of oxygen related to the stoichiometric metric value k 1, in order to reduce nitrogen oxide emissions, wherein a catalytic composition consisting essentially of at 15 least one element selected from a first group including tantalum, vanadium and niobium and at least one other element selected from a second group including zinc and the elements of groups IIIb, IVb and Vb of the Periodic Table is used.

Process for treating gases with a high oxygen content and which continuously have an excess of oxygen related to the stoichiometric value X 1, in order to reduce nitrogen oxide emissions, in which the gases are treated either in the presence of a reducing agent chosen from among a hydrocarbon or organic compound containing oxygen, or in the absence of a reducing agent, wherein a catalytic composition based on at least one

Claims

6. Process according to claim 2 or 4, wherein the elements from the group IIb are gallium or indium, the element from group IVb is tin and the elements from group Vb are antimony or bismuth.
7. Process according to any one of claims 1 to 6, wherein the composition further contains a support.
8. A process according to claim 7, wherein the support is selected from alumina, silica, titanium, oxide, zirconium oxide, lanthanide oxides, spinel-type oxides, zeolites, 10 silicates, crystalline silicoaluminium phosphates and crystalline aluminium phosphates.
9. Process according to claim 7, wherein the composition includes a support made of cerium oxide. S 10. Process according to any one of claims 1 to 4 and 6 to 9, wherein the gases are treated either in the presence of a reducing agent, or in the absence of a reducing agent. S" 15 11. Process according to claim 10 wherein the reducing agent is a hydrocarbon or o o 9 organic compound. 99•°99 S 12. Process according to any one of the preceding claims, wherein the gases have an oxygen content (expressed in volume) of at least
13. Process according to claim 12, when the gases have an oxygen content of at least
14. Process according to any one of the preceding claims wherein the gases treated are exhaust gases from internal combustion engines. -47- Use of compositions as defined in any one of the preceding claims in the manufacture of catalysts or catalytic devices for motor vehicle post-combustion.
16. A process for treating gases with a high oxygen content as claimed in any one of claims 1 to 14, substantially as herein described with reference to any one of the examples. DATED this 2nd Day of November 1998 RHONE-POULENC CHIMIE Attorney: RUTH M. CLARKSON Fellow Institute of Patent Attorneys of Australia of BALDWIN SHELSTON WATERS *e S f 48 ABSTRACT CATALYTIC COMPOSITIONS FOR THE REDUCTION OF NITROGEN OXIDES, BASED ON TANTALUM, VANADIUM, NIOBIUM, COPPER OR ANTIMONY A catalytic composition for reducing the content of nitrogen oxides in a gas having a high oxygen content, which composition is based on at least one element selected from tantalum, vanadium, niobium and antimony, or is based on at least one element selected from tantalum, vanadium, niobium, antimony and copper, and on at least one other element selected from zinc and the elements of groups IIIb, IVb and Vb of the Periodic Table, or which comprises copper and at least one other element selected from group Via of the Periodic Table.