Use of mixed oxides as oxygen storage components

Abstract

The present invention is concerned with the use of certain oxygen storage components. In particular, the use of special mixed oxides as oxygen storage components in exhaust catalysis is disclosed.

Claims

1. An automotive exhaust catalyst comprising an oxygen storage component, said oxygen storage component comprising: a binary, ternary or higher mixed oxide consisting of the formula
(M1).sub.n(M2).sub.b(M3).sub.c(M4).sub.d(M5).sub.e(M6).sub.f(M7).sub.gO.sub.x wherein 0?a, b, c, d, e, f, g?20 with at least a and b>0; and x adapts a value to compensate the positive charge originating from the metal cations M1-M7 being selected from the group consisting of Fe, Mn, V, Nb, Ta, Mo, and W.

2. The automotive exhaust catalyst of claim 1, further comprising catalytically active precious metals selected from the group consisting of Cu, Ag, Au, Pt, Pd, Rh, Ru, Ir and mixtures thereof.

3. The automotive exhaust catalyst of claim 2, wherein the mixed oxide is supported on a high surface area refractory metal oxide support having a surface area of at least 50 m.sup.2/g.

4. The automotive exhaust catalyst of claim 1, wherein the mixed oxide is supported on a high surface area refractory metal oxide support having a surface area of at least 50 m.sup.2/g.

5. The automotive exhaust catalyst of claim 1, wherein a is from >0-20, b is from >0-20, c is from 0-5 and d, e, f, g is from 0-5.

6. The automotive exhaust catalyst of claim 1, wherein only M1-M5 are present and selected from the group consisting of Fe, Mn, V, Nb and W.

7. The automotive exhaust catalyst of claim 1, wherein the oxygen storage component has an absolute oxygen storage capacity of at least 8000 ?g O.sub.2/mmol oxygen storage component.

8. The automotive exhaust catalyst of claim 1, which is free of ceria.

9. A method for storing oxygen in exhaust catalysis, comprising: introducing onto a support a binary, ternary or higher mixed oxide consisting of the formula
(M1).sub.a(M2).sub.b(M3).sub.c(M4).sub.d(M5).sub.e(M6).sub.f(M7).sub.gO.sub.x wherein 0?a, b, c, d, e, f, g?20 with at least a and b>0; and x adapts a value to compensate the positive charge originating from the metal cations M1-M7 being selected from the group consisting of Fe, Mn, V, Nb, Ta, Mo, and W as an oxygen storage component, and supplying exhaust gas to the binary, ternary or higher mixed oxide.

10. The method of claim 9, further comprising introducing onto the support catalytically active precious metals selected from the group consisting of Cu, Ag, Au, Pt, Pd, Rh, Ru, Ir and mixtures thereof.

11. The method of claim 9, wherein the mixed oxide is supported on a high surface area refractory metal oxide support having a surface area of at least 50 m.sup.2/g.

12. The method of claim 9, wherein a is from >0-20, b is from >0-20, c is from 0-5 and d, e, f, g is from 0-5.

13. The method of claim 9, wherein only M1-M5 are present and selected from the group consisting of Fe, Mn, V, Nb and W.

14. The method of claim 9, wherein the oxygen storage component has an absolute oxygen storage capacity of at least 8000 ?g O.sub.2/mmol oxygen storage component.

Description

EXAMPLES

Example 1: 1 w % Pd/10 w % CeO2 on Al2O3 (Comparative Sample)

(1) The catalyst material was prepared by pore volume impregnation of a Al.sub.2O.sub.3 powder with a mixture of an aqueous solution of Pd(NO.sub.3).sub.2 and (NH.sub.4).sub.2Ce(NO.sub.3).sub.6. After drying, the sample was calcined in static air for 4 h at 700? C.

Example 2: 1 w % Pd/10 w % VNbO5 on Al2O3

(2) The catalyst material was prepared by pore volume impregnation of a Al.sub.2O.sub.3 powder with a mixture of an aqueous solution of Pd(NO.sub.3).sub.2, Vanadyloxalate and Ammonium Niobium oxalate. After drying, the sample was calcined in static air for 4 h at 700? C.

Example 3: 1 w % Pd/10 w % FeVO4 Supported on Al2O3

(3) The catalyst material was prepared by pore volume impregnation of a Al.sub.2O.sub.3 powder with a mixture of an aqueous solution of Pd(NO.sub.3).sub.2, Vanadyloxalate and Iron nitrate. After drying, the sample was calcined in static air for 4 h at 700? C.

(4) Referring to FIG. 1 and Table 1 the redox activity characteristics are compared for the samples 1 w % Pd/10 w % CeO.sub.2 on Al.sub.2O.sub.3 (comparative example), 1 w % Pd/10 w % VNbO.sub.5 on Al.sub.2O.sub.3 and 1 w % Pd/10 w % FeVO.sub.4 supported on Al.sub.2O.sub.3. It is seen that the oxygen storage materials based on the oxygen storage components described in this patent show enhanced properties compared to the CeO.sub.2 containing comparative example. This is further demonstrated in Table 1, where the maxima in reduction temperatures are recorded as well as the relative oxygen storage capacity (in %), the absolute hydrogen uptake capacity (in ?g H.sub.2/mmol oxygen storage component), and the absolute oxygen storage capacity (in ?g O.sub.2/mmol oxygen storage component) of the oxygen storage components.

(5) TABLE-US-00002 TABLE 2 Compilation of the data obtained from H2 TPR absolute absolute hydrogen oxygen uptake storage relative capacity capacity oxygen (?g H.sub.2/mmol (?g O.sub.2/mmol H.sub.2 TPR storage oxygen oxygen Peak capacity storage storage position, (%); component); component); Material ? C. RT-700? C. RT-700? C. RT-700? C. Redox reaction Example1 107 31 306 2448 CeO.sub.2 .fwdarw. Ce.sub.2O.sub.3 (comparative example) +IV .fwdarw. +III Example2 109 81 1617 12936 VNbO.sub.5 .fwdarw. VNbO.sub.3 +V/+V .fwdarw. +III/+III Example3 95 68 2048 16384 FeVO.sub.4 .fwdarw. Fe.sub.2V.sub.2O.sub.5 +III/+V .fwdarw. +II/+III