| As one of the major factors in air pollution, carbon monoxide mainly comes from the incomplete combustion of hydrocarbons in automobile exhaust together with other fossil fuels. The catalysts play a key role in eliminating CO emission effectively, thus by far great efforts have been made to seek the catalysts with high activity, high stability and low cost for CO catalytic oxidation. Besides, an excellent high temperature catalyst still requires not only the active components to possess good anti-oxidation and anti-sinteration, but also the supports to be highly strong to avoid being collapsed or deformed during the practical use.In this paper, the commercial silicon carbide powder (labelled as SiCas-received) was surfacely oxided by HNO3 followed with modification via Ce, Zr doping. A series of Pt, Pd and PtPd catalysts supported on CeO2/SiC, Zr2O3/SiC and CeO2-Zr2O3/SiC were then prepared and characterized by BET, FTIR, XRD, TEM, XPS and UV-Vis. The catalytic performance of the obtained catalysts for CO oxidation was evaluated on a self-made equipment, so-called continuous flow microreactor-gas chromatography evaluation instrument. The effects of preparing conditions (surface modification, deposition method, rare earth metals ratio, active components ratio, etc.) on the catalytic activity and stability of the catalysts for CO oxidation were investigated systematically. In addition, the high temperature activity and anti-aging capability were studied as well. The main results and conclusions are as follows:(1) After acidic oxidation by nithite, the amount of SiO2 on SiC surface increased and thus was in favor of Ce、Zr doping. The specific surface of the composite support modified by Ce、Zr increased from 16 m2/g to 70.6 m2/g, which facilitated the dispersion of active metal particles of platinum and pladium. As a result, the catalytic activity and stability of the supported catalysts were strongly improved, especially for the case of two rear earth metals doping simultaneously. For single Ce or Zr doped, the best catalytic performance were achieved with both Ce and Zr doped amount of 8 wt.%, respectively. Among which, the T100 (the lowest temperature for 100% transformation rate of CO) value of Pt1/Ce8/SiC, Pt1/Zr8/SiC, Pd1/Ce8/SiC and Pd1/Zr8/SiC were 198℃,209℃,219℃ and 258℃, respectively. For Ce and Zr co-doped SiC supported catalysts, the T100 of Pt1/Ce3Zr5/SiC and Pd1/Ce3Zr5/SiC were 128℃ and 158℃, respectively.(2) Pt.Pd/Ce3Zr5/SiC and Pt/Pd/Ce3Zr5/SiC with different platinum and palladium loading amount were prepared by co-deposition and fractional deposition, respectively, using Ce3Zr5/SiC as the support. The effects of the deposition method, the metal loading order together with the relative amount of active components, etc. on the properties of the catalysts and their catalytic activity and stability for CO oxidation were investigated. The results indicated that the catalysts prepared by fractional deposition (Pt/Pd/Ce3Zr5/SiC) possess better catalytic performance in comparing to those prepared by co-deposition. In particular, the T100 value of Pt0.5/Pd0.5/Ce3Zr5/SiC was low to 110℃, showing the highest activity.(3) To investigate the high temperature activity and the aging resistance of the catalysts, the best catalyst hereinto, Pt0.5/Pd0.5/Ce3Zr5/SiC, was applied in CO continuous catalytic oxidation at 500℃ for 120 hrs. The results obviously showed that the activity of the catalyst almost kept constant, the conversion rate could still reach up to 99% and beyond. Moreover, the catalyst could be completely recoved by reduction process after being exposed in air for a long time (60 days for example). |
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