USE OF VANADATES AS OXIDATION CATALYSTS

Abstract

Use of a ternary vanadate of formula (I): Fe.sub.x MeI.sub.y MeII.sub.z VO.sub.4 wherein MeI and MeII are different from each other and each stand for an element selected from the group consisting of Y, La, Ce, Pr, Nd, Sm, Er, Gd, Tb, Dy, Ho, Tm, Yb, Lu, Al, Bi and Sb and wherein x=0.05-0.9; y=0.05-0.9; z=0.05-0.9; x+y+z=1, as a catalyst for the oxidation of carbonaceous compounds in combustion engines.

Claims

1. A method of catalytically oxidizing carbonaceous compounds from a combustion engine, comprising: contacting a catalyst comprising a ternary vanadate of formula (I) with carbonaceous compounds from the combustion engine:
Fe.sub.x MeI.sub.y MeII.sub.z VO.sub.4 (I), wherein MeI and MeII are different from each other and each stand for an element selected from the group consisting of Y, La, Ce, Pr, Nd, Sm, Er, Gd, Tb, Dy, Ho, Tm, Yb, Lu, Al, Bi and Sb and wherein x=0.050.9 y=0.050.9 z=0.050.9 x+y+z=1, the catalyst catalysing oxidation of the carbonaceous compounds from the combustion engine.

2. The method according to claim 1, wherein MeI and MeII each stand for an element selected from the group consisting of Y, La, Ce, Pr, Er, Al, Bi.

3. The method according to claim 1, wherein MeI and MeII each stand for an element selected from the group consisting of Ce, La, Er, Al and Bi.

4. The method according to claims 1, wherein MeI and MeII are selected from the group of the following combinations: MeI=La, MeII=Er, MeI=Ce, MeII=Al MeI=Ce, MeII=Bi, MeI=La, MeII=Al, MeI=Er, MeII=Al, and MeI=Bi, MeII=Al.

5. The method according to claims 1, wherein x=0.1-0.8 y=0.1-0.8 z=0.1-0.8 x+y+z=1.

6. The method according to claim 5, wherein x=0.2-0.6 y=0.2-0.6 z=0.2-0.6 x+y+z=1.

7. The method according to claim 1, wherein the ternary vanadate is selected from the group consisting of: Fe.sub.0.33Ce.sub.0.34Al.sub.0.33VO.sub.4, Fe.sub.0.5Ce.sub.0.25Al.sub.10.25VO.sub.4, Fe.sub.0.33Ce.sub.0.34Bi.sub.0.33VO.sub.4, Fe.sub.0.25Ce.sub.0.5Bi.sub.0.25VO.sub.4, Fe.sub.0.25Ce.sub.0.25Bi.sub.0.5VO.sub.4, Fe.sub.0.5La.sub.0.25Er.sub.0.25VO.sub.4, Fe.sub.0.33La.sub.0.34Al.sub.0.33VO.sub.4, Fe.sub.0.33Er.sub.0.34Al.sub.0.33VO.sub.4, and Fe.sub.0.33Al.sub.0.33Bi.sub.0.34VO.sub.4.

8. The method according to claim 1, wherein the ternary vanadate is employed in combination with another compound selected from oxides, oxide precursors of Al, Ti, Ce, Zr, and mixtures thereof

9. (canceled)

10. A method of catalytically oxidizing exhaust gas from a combustion engine, comprising: contacting a catalyst comprising a ternary vanadate of formula (I) with exhaust gas from the combustion engine:
Fe.sub.x MeI.sub.y MeII.sub.z VO.sub.4 (I), wherein MeI and MeII are different from each other and each stand for an element selected from the group consisting of Y, La, Ce, Pr, Nd, Sm, Er, Gd, Tb, Dy, Ho, Tm, Yb, Lu, Al, Bi and Sb and wherein x=0.05-0.9 y=0.05-0.9 z=0.05-0.9 x+y+z=1, the catalyst promoting oxidation of the exhaust gas from the combustion engine.

11. The method according to claim 10, the catalyst promoting oxidation of soot in the exhaust gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0022] Surprisingly it has been discovered that ternary vanadates as defined above show unexpected positive effects for oxidation of diesel exhaust particulates in the catalytic oxidation of (diesel) soot.

[0023] Specifically, the compounds used according to the present invention show a better catalytic activity (expressed as a lower T.sub.50-value) compared with state of the art materials e.g. with FeVO.sub.4 or CeVO.sub.4,preferably in comparison to both FeVO.sub.4 and CeVO.sub.4, which may be defined as reference materials. The T.sub.50-value is defined as the temperature at which 50% (w/w) of soot in a mixture containing catalyst and soot is oxidized.

[0024] Furthermore, the compounds used according to the present invention also show a better thermal stability compared with aged state of the art materials. The term thermal stability according to the present invention means the catalytic activity characterized by the T.sub.50-value of the catalyst compositions measured after thermal ageing.

[0025] The thermal ageing of the compositions of the present invention is performed in the range between 700 C. to 850 C./10 h, more preferably 750 C.-850 C./10 h , most preferably 800 C.-850 C./10 h.

[0026] The thermal stability of these thermally aged compositions of the present invention is better compared to e.g. thermally aged FeVO.sub.4 or thermally aged CeVO.sub.4, preferably in comparison to both thermally aged FeVO.sub.4 and thermally aged CeVO.sub.4, which may be defined as reference materials. Better catalytic activity and, especially, better thermal stability allows a safer use in industrial applications and might also improve longevity of the catalysts.

[0027] According to the present invention, the ternary vanadates of formula (I) are used in oxidation catalysts. The functioning principle of an oxidation catalyst relies on its capability to catalyze oxidation of carbonaceous compounds using oxygen or other oxidizing agents. The carbonaceous compounds can be e.g. soot, carbon monoxide, dioxins, methane, NMHC (non-methane hydrocarbons), methanol, NMVOC (non-methane volatile organic compounds), aromatic hydrocarbons, preferably soot, dioxin and methane, more preferably soot and dioxin and most preferably soot.

[0028] The vanadates used according to the present invention can be prepared as solid-solid solution, physical mixtures and combinations thereof.

[0029] For the purpose of the present specification and claims, the term rare earth element (REE) means a rare earth element or a mixture thereof, e. g. more than one rare earth element. According to IUPAC a rare earth metal is an element from the fifteen lanthanides, as well as scandium and yttrium.

[0030] In a preferred embodiment of the present invention in the above-indicated formula MeI and MeII each stands for an element selected from the group consisting of Y, La, Ce, Pr, Er, Al and Bi. Even more preferably, MeI and MeII each stands for an element selected from the group consisting of Ce, La, Er, Al and Bi.

[0031] The present invention also refers to the use of ternary vanadates as oxidation catalysts of general formula Fe.sub.x MeI.sub.y MeII.sub.z VO.sub.4, wherein MeI and MeII are selected from the group of the following combinations:

[0032] MeI=La, MeII=Er

[0033] MeI=Ce, MeII=Al

[0034] MeI=Ce, MeII=Bi

[0035] MeI=La, MeII=Al

[0036] MeI=Er, MeII=Al

[0037] MeI=Bi, MeII=Al.

[0038] In a further preferred embodiment, in the ternary vanadates of formula (I)

[0039] x is 0.1-0.8

[0040] y is 0.1-0.8,

[0041] z is 0.1-0.8,

[0042] x+y+z=1.

[0043] In a further preferred embodiment,

[0044] x is 0.2-0.6

[0045] y is 0.2-0.6

[0046] z is 0.2-0.6,

[0047] x+y+z=1.

[0048] Particularly, in a preferred embodiment of the present invention the ternary vanadate used according to the present invention is selected from the group consisting of

[0049] Fe.sub.0.33Ce.sub.0.34Al.sub.0.33VO.sub.4

[0050] Fe.sub.0.5Ce.sub.0.25Al.sub.0.25VO.sub.4

[0051] Fe.sub.0.33Ce.sub.0.34Bi.sub.0.33VO.sub.4

[0052] Fe.sub.0.25Ce.sub.0.5Bi.sub.0.25VO.sub.4

[0053] Fe.sub.0.25Ce.sub.0.25Bi.sub.0.5VO.sub.4

[0054] Fe.sub.0.5La.sub.0.25Er.sub.0.25VO.sub.4

[0055] Fe.sub.0.33La.sub.0.34Al.sub.0.33VO.sub.4

[0056] Fe.sub.0.33Er.sub.0.34Al.sub.0.33VO.sub.4

[0057] Fe.sub.0.33Al.sub.0.33Bi.sub.0.34VO.sub.4.

[0058] In a further preferred embodiment of the present invention these ternary vanadate used according to the present invention exhibit T.sub.50 values of 450 C. or below, more preferably T.sub.50-values of 440 C. or below, most preferably T.sub.50 of 430 C. or below after calcination at 650 C. for 2 hours.

[0059] The ternary vanadates employed according to the present invention can be prepared in a manner as known to the skilled artisan, such as from WO 2011/127505 A1.

[0060] The ternary vanadates employed according to the present invention are preferably prepared by means of a co-precipitation synthesis. The stoichiometric amounts of the nitrates of the elements to be included in the formulation were dissolved in deionized water to yield a mixed metal nitrate solution. Bismuth nitrate hydrate (Bi(NO.sub.3).sub.3*5 H.sub.2O) represented an exception because not being soluble in water it had to be dissolved in an acidic solution containing HNO.sub.3. Another aqueous solution was simultaneously prepared with the stoichiometric amount of ammonium metavanadate (NH.sub.4VO.sub.3) at 80 C. The two solutions were combined under continuous stirring and the pH adjusted by addition of ammonia solution. The precipitate so formed was further stirred, filtered, washed several times with deionized water and dried at 120 C. overnight. The dried material was calcined at 650 C. for 2 hours.

[0061] Ternary vanadates can also be synthesized by solid phase reactions or physical mixtures of vanadates.

[0062] In a further preferred embodiment of the present invention the ternary vanadate according to the present invention is employed in combination with a further compound selected from oxides or oxide precursors of Al, Ti, Ce, Zr and mixtures thereof.

[0063] The further compound can also be doped (up to 20%) with one or more rare earth elements other than cerium.

[0064] Oxide precursors for Al are for example boehmite, aluminium hydroxide, aluminium nitrate, aluminium chloride and others, preferably boehmite and aluminium hydroxide, most preferably boehmite.

[0065] Oxide precursors of Ti are for example: metatitanic acid, titanyl sulfate, titanium chloride and others, preferably metatitanic acid.

[0066] Oxide precursors of Zr are for example: zirconium hydroxide, zirconyl hydroxide, zirconyl nitrate, zirconium nitrate, zirconyl carbonate, zirconium basic carbonate, zirconyl chloride and others, preferably zirconium hydroxide and zirconyl hydroxide.

[0067] Oxide precursors of Ce are for example: cerium hydroxide, cerium chloride, cerium hydrate, cerium sol, cerium nitrate, cerium carbonate, cerium oxalate, cerium ammonium nitrate and others, preferably cerium hydroxide, cerium hydrate and cerium sol.

[0068] More preferred is the use with this further compound comprising TiO.sub.2 or Al.sub.2O.sub.3 or Ce.sub.aZr.sub.(1-a)O.sub.2, such as Ce.sub.0.75Z.sub.0.25O.sub.2 or mixtures thereof.

[0069] The ratio of the vanadates and the further compound should be between 100:0 and 10:90 by weight, more preferably 100:0 and 30:70 by weight and most preferably 100:0 and 50:50 by weight.

[0070] Finally, in yet another aspect of the present invention the ternary vanadates of formula (I) are used for oxidative exhaust gas catalysis, especially for soot oxidation.

[0071] The present invention will now be explained in more detail with reference to examples and comparative examples without being limited to these. Temperatures indicated are in degree Celsius ( C.).

[0072] Synthesis

Example 1Fe.SUB.0.33.Ce.SUB.0.34.Al.SUB.0.33.VO.SUB.4

[0073] Fe.sub.0.33Ce.sub.0.34Al.sub.0.33VO.sub.4 was prepared by the co-precipitation method. To obtain 3000 mg of powder catalysts, 1847.2 mg of ammonium metavanadate NH.sub.4VO.sub.3 (AMV) (Sigma Aldrich, Vienna) were dissolved in 157.9 g distilled water at 80 C. in order to obtain a 0.1 mol/l solution; a second solution was prepared by dissolving 2105.2 mg of iron nitrate nonahydrate Fe(NO.sub.3).sub.3. 9H.sub.2O (Treibacher Industrie AG (TIAG), Althofen), 2331.6 mg of cerium nitrate hexahydrate Ce(NO.sub.3).sub.3. 6H.sub.2O (TIAG, Althofen) and 1954.7 mg of aluminium nitrate nonahydrate Al(NO.sub.3).sub.3.9H.sub.2O (Sigma Aldrich, Vienna) in 157.9 g of distilled water. The two solutions were mixed under continuous stirring and pH was adjusted to 7 with the addition of aqueous ammonia solution (28 vol %). This caused the precipitation of a brown compound (Fe.sub.0.33Ce.sub.0.34Al.sub.0.33VO.sub.4) which was filtered off, washed several times with distilled water and dried at 100 C. overnight and calcined at 650 C. for 2h under air in a muffle furnace.

Example 2 to 9

[0074] The compositions referred to examples 2 to 9 are as disclosed in Tables 1A and 1B below and were prepared analogously to the procedure as disclosed in example 1 but with the different appropriate starting materials and amounts. The quantities of the starting materials used for the preparation according to Examples 2 to 9 are listed in Tables 1A and 1B. In case of vanadates containing Bi 0.2 ml of nitric acid were added to the mixed metal solution.

TABLE-US-00001 TABLE 1a Fe(NO.sub.3).sub.3*9 Al(NO.sub.3).sub.3*9 Ce(NO.sub.3).sub.3*6 AMV H.sub.2O H.sub.2O H.sub.2O Ex. Composition [g] [g] [g] [g] 1 Fe.sub.0.33Ce.sub.0.34Al.sub.0.33VO.sub.4 1.8472 2.1052 1.9547 2.3316 2 Fe.sub.0.5Ce.sub.0.25Al.sub.0.25VO.sub.4 1.9000 3.2808 1.5231 1.7634 3 Fe.sub.0.33Ce.sub.0.34Bi.sub.0.33VO.sub.4 1.4082 1.6534 1.7251 4 Fe.sub.0.25Ce.sub.0.5Bi.sub.0.25VO.sub.4 1.3965 1.2057 2.5922 5 Fe.sub.0.33Er.sub.0.34Al.sub.0.33VO.sub.4 1.7628 2.0088 1.8652 6 Fe.sub.0.33La.sub.0.34Al.sub.0.33VO.sub.4 1.8524 2.1111 1.9603 7 Fe.sub.0.33Bi.sub.0.34Al.sub.0.33VO.sub.4 1.6454 1.8752 1.7413 8 Fe.sub.0.25Ce.sub.0.25Bi.sub.0.5VO.sub.4 1.3076 1.1290 1.2135 9 Fe.sub.0.5La.sub.0.25Er.sub.0.25VO.sub.4 1.5999 2.7627

TABLE-US-00002 TABLE 1b H.sub.2O for H.sub.2O for Er(NO.sub.3).sub.3*6H.sub.2O Bi(NO.sub.3).sub.3*5H.sub.2O La(NO.sub.3).sub.3*6H.sub.2O AMV Nitrates Ex. Composition [g] [g] [g] [g] [g] 1 Fe.sub.0.33Ce.sub.0.34Al.sub.0.33VO.sub.4 157.9 157.9 2 Fe.sub.0.5Ce.sub.0.25Al.sub.0.25VO.sub.4 162.4 162.4 3 Fe.sub.0.33Ce.sub.0.34Bi.sub.0.33VO.sub.4 1.9272 120.4 120.4 4 Fe.sub.0.25Ce.sub.0.5Bi.sub.0.25VO.sub.4 1.4479 119.4 119.4 5 Fe.sub.0.33Er.sub.0.34Al.sub.0.33VO.sub.4 2.3635 150.7 150.7 6 Fe.sub.0.33La.sub.0.34Al.sub.0.33VO.sub.4 2.3313 158.4 158.4 7 Fe.sub.0.33Bi.sub.0.34Al.sub.0.33VO.sub.4 2.3198 140.7 140.7 8 Fe.sub.0.25Ce.sub.0.25Bi.sub.0.5VO.sub.4 2.7112 111.8 111.8 9 Fe.sub.0.5La.sub.0.25Er.sub.0.25VO.sub.4 1.5775 1.4806 136.8 136.8

Example 10 Physical Mixture of 0.33 FeVO.SUB.4., 0.34 CeVO.SUB.4., 0.33Al VO.SUB.4

[0075] For a physical mixture of single calcined vanadates the net weight of the single calcined vanadates were calculated to achieve the final formal composition Fe.sub.0.33Ce.sub.0.34Al.sub.0.33VO.sub.4. FeVO.sub.4 was prepared as described in comparative example 5. CeVO.sub.4 was prepared as described in comparative example 2. AlVO.sub.4 was prepared in the same manner using 2471.9 mg AMV and 211.3 g of distilled water and 7926.3 mg Al(NO.sub.3).sub.3*9 H.sub.2O and 211.3 g of distilled water.

[0076] The corresponding mixture was obtained by mixing 890.4 mg of calcined FeVO.sub.4, 1369.8 mg calcined CeVO.sub.4 and 739.8 mg calcined AlVO.sub.4 in a mortar for 10 minutes. After mixing no additional calcination was performed.

Example 11 Physical Mixture of 0.25 FeVO.SUB.4., 0.5 CeVO.SUB.4., 0.25 BiVO.SUB.4

[0077] For a physical mixture of single calcined vanadates the net weight of the single calcined vanadates were calculated to achieve the final formal composition Fe.sub.0.25Ce.sub.0.5Bi.sub.0.25VO.sub.4. FeVO.sub.4 was prepared as described in comparative example 5. CeVO.sub.4 was prepared as described in comparative example 2. BiVO.sub.4 was prepared in the same manner using 1083.0 mg AMV and 92.6 g of distilled water and 4491.6 mg Bi(NO.sub.3).sub.3*5H.sub.2O, 0.2 ml of nitric acid and 92.6 g of distilled water.

[0078] The corresponding mixture was obtained by mixing 509.9 mg of calcined FeVO.sub.4, 1523.0 mg calcined CeVO.sub.4 and 967.1 mg calcined BiVO.sub.4 in a mortar for 10 minutes. After mixing no additional calcination was performed.

Comparative Example 1Ce.SUB.0.5.Al.SUB.0.5.VO.SUB.4

[0079] Ce.sub.0.5Al.sub.0.5VO.sub.4 was prepared by the co-precipitation method. To obtain 3000 mg of powder catalysts, 1767.4 mg of ammonium metavanadate NH.sub.4VO.sub.3 (Aldrich) were dissolved in 151.1 g of distilled water at 80 C. in order to obtain a 0.1 mol/l solution; a second solution was prepared by dissolving 2833.7 mg of aluminium nitrate nonahydrate Al(NO.sub.3).sub.3. 9H.sub.2O (Aldrich) and 3280.6 mg of cerium nitrate hexahydrate Ce(NO.sub.3).sub.3. 6H.sub.2O (Treibacher) in 151.1 g of distilled water at 80 C. The two solutions were mixed under continuous stiffing and pH was adjusted to 7 with the addition of aqueous ammonia solution (28 vol %). This caused the precipitation of a light brown compound (Ce.sub.0.5Al.sub.0.5VO.sub.4) which was filtered off, washed several times with distilled water, dried at 100 C. overnight and calcined at 650 C. for 2h under air in a muffle furnace.

Comparative Example 2 to 6

[0080] The compositions referred to as comparative examples 2 to 6 are disclosed in Tables 2A and 2B below and were prepared analogously to the procedure as disclosed in comparative example 1 but using appropriate starting material and amounts. The quantities of the starting materials used for the preparation according to comparative examples 2 to 6 are as listed in

[0081] Tables 2A and 2B. In case of vanadates containing Bi 0.2 ml of nitric acid were added to the mixed metal solution.

TABLE-US-00003 TABLE 2A Fe(NO.sub.3).sub.3*9 Al(NO.sub.3).sub.3*9 Ce(NO.sub.3).sub.3*6 Comp. AMV H.sub.2O H.sub.2O H.sub.2O Ex. Composition [g] [g] [g] [g] 1 Ce.sub.0.5Al.sub.0.5VO.sub.4 1.7674 2.8337 3.2806 2 CeVO.sub.4 1.3754 5.1061 3 Er.sub.0.5La.sub.0.5VO.sub.4 1.3089 4 Fe.sub.0.5Al.sub.0.5VO.sub.4 2.2453 3.8772 3.6001 5 FeVO.sub.4 2.0540 7.0937 6 Fe.sub.0.3La.sub.0.7VO.sub.4 1.5324 1.5876

TABLE-US-00004 TABLE 2B H.sub.2O for H.sub.2O for Comp. Er(NO.sub.3).sub.3*6H.sub.2O Bi(NO.sub.3).sub.3*5H.sub.2O La(NO.sub.3).sub.3*6H.sub.2O AMV Nitrates Ex. Composition [g] [g] [g] [g] [g] 1 Ce.sub.0.5Al.sub.0.5VO.sub.4 151.1 151.1 2 CeVO.sub.4 117.6 117.6 3 Er.sub.0.5La.sub.0.5VO.sub.4 2.5814 2.4227 111.9 111.9 4 Fe.sub.0.5Al.sub.0.5VO.sub.4 191.9 191.9 5 FeVO.sub.4 175.6 175.6 6 Fe.sub.0.3La.sub.0.7VO.sub.4 3.9710 131.0 131.0

Comparative Example 7-8.4% FeVO.SUB.4./ 91.6% DT 58

[0082] Mixture made by slurry synthesis 8.4 wt. % FeVO.sub.4/DT-58 (TiO.sub.2/SiO.sub.2/WO.sub.3 81/10/9 weight %) purchased from Cristal, Thann)

[0083] To obtain 3000 mg of catalyst, 252 mg of FeVO.sub.4 (prepared as described in comparative example 5) and 2748 mg of DT-58 (TiO.sub.2/SiO.sub.2/WO.sub.3 (81/10/9 weight %) from Cristal) were mixed in distilled water under continuous stirring at ca. 100 C. After slow evaporation of water a wet cake was obtained. The catalyst was obtained after calcination at 650 C./2h.

Comparative Example 8-50% FeVO.SUB.4./50% DT 58

[0084] Mixture made by slurry synthesis 50 wt. % FeVO.sub.4/DT-58

[0085] To obtain 3000 mg of catalyst, 1500 mg of FeVO.sub.4 (prepared as described in comparative example 5) and 1500 mg of DT-58 (TiO.sub.2/SiO.sub.2/WO.sub.3 (81/10/9 weight %) purchased from Cristal, Thann) were mixed in distilled water under continuously stiffing at ca. 100 C. After slow evaporation of water a wet cake was obtained. The catalyst was obtained after calcination at 650 C./2h.

Comparative Example 9Physical Mixture of 0.3 FeVO.SUB.4., 0.7 LaVO.SUB.4

[0086] For a physical mixture of single calcined vanadates the net weight of the single calcined vanadates were calculated to achieve the final formal composition Fe.sub.0.3La.sub.0.7VO.sub.4. FeVO.sub.4 was prepared as described in comparative example 5. LaVO.sub.4 was prepared in the same manner using 1382.0 mg AMV and 118.1 g of distilled water and 5116.0 mg lanthanum nitrate hexahydrate La(NO.sub.3).sub.3*6H.sub.2O and 118.1 g of distilled water.

[0087] The corresponding mixture was obtained by mixing 671.4 mg of calcined FeVO.sub.4 and 2328.6 mg calcined LaVO.sub.4 in a mortar for 10 minutes. After mixing no additional calcination was performed.

[0088] Conditions for Catalytic Powder Testing

[0089] Sample Preparation and Thermal Ageing

[0090] The synthesized and calcined (650 C./2h) vanadates of the present invention were milled manually in an agate mortar. Powdered samples and carbon black (CB, Printex U) (Evonik Degussa GmbH, Essen) were carefully mixed in an agate mortar in a mass ratio of 20:1 for ten minutes until the mixture was homogeneous to result in a tight contact mode.

[0091] Optionally thermal ageing was employed to the powdered samples prior to mixing with carbon black. Ageing of samples was performed for 10 hours in a conventional muffle oven with a heating rate of 10 C./min at either 800 C. or 850 C. as indicated in table 3 below.

[0092] Measurement of the Catalytic Activity

[0093] Soot oxidation activity was determined by thermogravimetry analysis (TGA) (Q500, TA Instruments) under ambient atmosphere. Each sample (soot+catalyst, ca. 20 mg) was placed in a small flat Pt crucible and the total gas flow was set to 60 ml/min. The samples were pretreated for 1 h at 120 C. in order to desorb water. The soot combustion activities of the catalysts were measured under dynamic conditions with a heating ramp of 10 C./min in a temperature range of from 25 C. to 800 C. The temperature at which 50% of weight loss is observed (T.sub.50, corresponding to removal of 50% of soot) was used as a measure of catalytic activity.

[0094] The results of catalytic activity tests performed with the compounds obtained according to the examples above with or without previous thermal ageing are summarized in the following table:

TABLE-US-00005 TABLE 3 T.sub.50 [ C.] T.sub.50 [ C.] (calcined (calcined T.sub.50 [ C.] 650 C./2 h + 650 C./2 h + (calcined aged 800 aged 850 Sample Composition 650 C./2 h) C./10 h) C./10 h) Example 1 Fe.sub.0.33Ce.sub.0.34Al.sub.0.33VO.sub.4 431 421 399 Example 2 Fe.sub.0.5Ce.sub.0.25Al.sub.0.25VO.sub.4 434 Example 3 Fe.sub.0.33Ce.sub.0.34Bi.sub.0.33VO.sub.4 417 Example 4 Fe.sub.0.25Ce.sub.0.5Bi.sub.0.25VO.sub.4 400 Example 5 Fe.sub.0.33Er.sub.0.34Al.sub.0.33VO.sub.4 422 406 399 Example 6 Fe.sub.0.33La.sub.0.34Al.sub.0.33VO.sub.4 434 409 Example 7 Fe.sub.0.33Bi.sub.0.34Al.sub.0.33VO.sub.4 418 Example 8 Fe.sub.0.25Ce.sub.0.25Bi.sub.0.5VO.sub.4 412 Example 9 Fe.sub.0.5La.sub.0.25Er.sub.0.25VO.sub.4 437 Example 10 Fe.sub.0.33Ce.sub.0.34Al.sub.0.33VO.sub.4*) 439 Example 11 Fe.sub.0.25Ce.sub.0.5Bi.sub.0.25VO.sub.4*) 419 Comparative Ce.sub.0.5Al.sub.0.5VO.sub.4 465 Example 1 Comparative CeVO.sub.4 487 Example 2 Comparative Er.sub.0.5La.sub.0.5VO.sub.4 519 Example 3 Comparative Fe.sub.0.5Al.sub.0.5VO.sub.4 463 Example 4 Comparative FeVO.sub.4 452 437 464 Example 5 Comparative Fe.sub.0.3La.sub.0.7VO.sub.4 456 Example 6 Comparative FeVO.sub.4 (8.4%)/DT-58**) 520 Example 7 Comparative FeVO.sub.4 (50%)/DT-58**) 474 Example 8 Comparative Fe.sub.0.3La.sub.0.7VO.sub.4*) 485 Example 9 *)made via physical mixture without calcination of the final product (educts were calcined) **)DT-58 = TiO.sub.2/SiO.sub.2/WO.sub.3 (81/10/9 weight %)