Catalyst for the oxidation of CO and HC at low temperatures

Abstract

The present invention relates to a catalyst for the removal of carbon monoxide and hydrocarbon from the exhaust gas of lean-operated internal combustion engines on a supporting body, which bears platinum and/or palladium on one or more refractory carrier materials and also contains cerium oxide and which, after reductive treatment at 250° C. and after CO adsorption, is characterized by certain peaks in Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), and also relates to the use thereof for removing carbon monoxide and hydrocarbon from the exhaust gas of lean-operated internal combustion engines.

Claims

1. A catalyst for removing carbon monoxide and hydrocarbon from the exhaust gas of lean-operated internal combustion engines on a supporting body, comprising (i) platinum, or platinum and palladium, on one or more refractory carrier material; and (ii) cerium oxide present in an amount of 50 to 150 g/L relative to the volume of the supporting body, wherein, after reductive treatment at 250° C. and after CO adsorption, the catalyst shows peaks at wavenumbers 2906 cm.sup.−1 (5 cm.sup.−1), 2879 cm.sup.−1 (±5 cm.sup.−1), and 2847 cm.sup.−1 (±5 cm.sup.−1) in Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), and wherein a ratio of peak heights at wavenumber 2879 cm.sup.−1 to wavenumber 2906 cm.sup.−1 is greater than 0.4, and a ratio of peak heights at wavenumber 2847 cm.sup.−1 to wavenumber 2906 cm.sup.−1 is also greater than 0.4.

2. The catalyst according to claim 1, wherein the quantity of platinum, or platinum and palladium, is 0.5 to 10% by weight relative to component (i).

3. The catalyst according to claim 1, wherein the quantity of platinum, or platinum and palladium, is 1 to 5% by weight relative to component (i).

4. The catalyst according to claim 1, wherein the catalyst comprises platinum and palladium, and the weight ratio of Pt:Pd is 1:1 to 20:1.

5. The catalyst according to claim 1, wherein aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, cerium oxide, zeolite, or mixtures or mixed oxides thereof are used as refractory carrier materials of component (i).

6. A method for removing carbon monoxide and hydrocarbon from the exhaust gas of lean-operated internal combustion engines, comprising passing the exhaust gas over a catalyst according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows the CO conversion of sample catalyst K1 and comparative catalyst VK1 as a function of the temperature after pre-treatment in oxidizing atmosphere.

(2) FIG. 2 shows DRIFTS measurements (Diffuse Reflectance Infrared Fourier Transform Spectroscopy) of catalysts K1 and VK11 after adsorption of CO in the range of 3000-2600 cm.sup.−1.

(3) FIG. 3 shows the CO conversions of the inventive sample catalysts K2 and K3 shown together with that of comparative catalyst VK2.

(4) FIG. 4 shows corresponding DRIFTS spectra following reductive pre-treatment and CO adsorption.

(5) FIG. 1 shows the CO conversion of sample catalyst K1 and comparative catalyst VK1 as a function of the temperature after pre-treatment in oxidizing atmosphere (conditioning 1; thin line) at temperatures up to 500° C. and after pre-treatment with 3× reducing atmosphere (conditioning 2; thick line) for 5 s at 250° C. While the CO conversion behavior of VK1 is relatively independent of the pre-treatment, the CO conversion activity of sample catalyst K1 through pre-treatment in reducing atmosphere is clearly increased, i.e., the temperature T.sub.90, at which the conversion reaches 90%, sinks to 98° C. In FIG. 2, DRIFTS measurements (Diffuse Reflectance Infrared Fourier Transform Spectroscopy) of catalysts K1 and VK11 after adsorption of CO in the range of 3000-2600 cm.sup.−1, which correspond to the formation of formate species on the surface, are shown. While no peaks form with either catalyst after oxidative pre-treatment (light curves), the spectra following reductive pre-treatment (dark curves) are very different. While no formate species were formed with comparative catalyst VK1 (only one peak at wavenumber 2906 cm.sup.−1 is recognizable), the peaks at wavenumbers 2879 cm.sup.−1 and 2847 cm.sup.−1 show the presence of reactive centers for comparative catalyst 1.

(6) In FIG. 3, the CO conversions of the inventive sample catalysts K2 and K3 are shown together with that of comparative catalyst VK2. Although all catalysts have a similar composition, differences in the conversion following reductive pre-treatment can be clearly seen. Thus, the T.sub.90 values for K2 and K3 are 85° C. and 140° C., while the T.sub.90 value for VK2 is 215° C. The corresponding DRIFTS spectra following reductive pre-treatment and CO adsorption are shown in FIG. 4. (The curves of the fresh samples are also still included here. These need to be removed.) While peaks in the range of wavenumbers 2906 cm.sup.−1, 2879 cm.sup.−1, and 2847 cm.sup.−1 have clearly formed for the inventive catalysts K2 and K3, these are not recognizable in comparative catalyst VK2. It is thus critical to the inventive catalyst that the above-listed DRIFTS peaks be present following CO adsorption.

(7) The following table summarizes the results:

(8) TABLE-US-00004 CO Intensity at Peak ratios conversion 2906.sup.−1 2879.sup.−1 2874.sup.−1 2879/2906 2847/2906 T90 [° C.] K1 0.0191 0.0194 0.0292 1.0 1.5 98 VK1 0.0078 <0.005 <0.005 — — 200 K2 0.0247 0.0571 0.0415 2.3 1.7 90 K3 0.0084 0.0125 0.0111 1.5 1.3 140 VK2 <0.005 <0.005 <0.005 — — 220