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Palladium Doped In Ceria-lanthanum Oxides Directly Washcoated Monolithic Catalysts For Catalytic Combustion

Posted on:2010-11-05Degree:MasterType:Thesis
Country:ChinaCandidate:L YueFull Text:PDF
GTID:2121360278468497Subject:Physical chemistry
Abstract/Summary:PDF Full Text Request
Air pollutions by volatile organic compounds (VOCs) has drawn considerable attention in recent years. Among the technologies developed for the treatment of VOCs, the catalytic combustion is considered to be a promising technology due to its simple equipment and eliminating VOCs at relatively low temperatures. The catalyst is the key of catalytic combustion technology. CeO2-based mixed oxides have been widely investigated due to their excellent oxygen storage capacity, high thermal stability, enhanced redox, while the Pd-based catalyst has been applied to catalytic combustion due to its high activity. So, the aim of the thesis is to develop a novel CeO2-La2O3 mixed oxides washcoat on the cordierite monolith, which is used as the washcoat of the Pd-based monolithic catalyst. The catalytic activity behavior and thermal stability of the monolithic catalysts for toluene combustion were investigated. In addition, the washcoats and their supported-Pd catalysts were characterized by XRD, Raman spectroscopy, H2-TPR and SEM techniques. The main contents and results in this thesis can be summarized as follows:1 .A novel CexLa1-xOδwashcoat has been prepared by an impregnation method, which acts as a host for the active Pd component to prepare a series of the Pd/CexLa1-xOδ/substrate (x=1, 0.8, 0.6 and 0.5) monolithic catalysts for toluene combustion. The results indicate that the washcoat shows excellent adhesion to the substrate according to an ultrasonic test. The order of the catalytic activity in terms of x is 0.8>0.6>1>0.5. There is strong interaction exists among palladium, CeO2-La2O3 solid solution and the substrate. The interaction changes the redox property and influences on the catalytic activity of the catalysts. 2.The effect of calcination temperature on the Pd/Ce0.8La0.2Oδ/substrate monolithic catalyst for toluene combustion was investigated. The results indicate that when the calcination temperature is around 500℃, the uniform and densely packed particles deposit onto the surface of the substrate, implying that the washcoat is well distributed on the substrate. The homogeneous washcoat is very favorable for the dispersion of the active phase and the improvement of the catalytic activity. The Pd/Ce0.8La0.2Oδ/substrate monolithic catalyst calcined at 500℃exhibits the highest catalytic activity, over which toluene conversion is up to 90 % at a temperature as low as 210℃. The catalytic activities of the monolithic catalysts calcined at different temperatures decrease with raising calcination temperature. This result may be attributed to the sintering of the PdO particles and CeO2-La2O3 mixed oxides particles and the decrease in the surface area. In addition, the thermal stability may be associated with the formation of CeO2-La2O3 solid solution and the stable presence of PdO phase at high temperatures. Compared with the Pd/Ce0.8Zr0.2O2 monolithic catalysts, the thermal stability of the Pd/Ce0.8La0.2Oδmonolithic catalyst did not has significantly improvement.3.Pd/Ce0.8Zr0.15La0.05Oδand Pd/Ce0.8Zr0.2O2monolithic catalysts were prepared by an impregnation method, by which the active component (Pd) and CeO2-ZrO2-La2O3 (CeO2-ZrO2) coat simultaneously impregnated on the corderite substrat. Combining with X-ray diffraction (XRD), Raman spectroscopy, Nitrogen sorption, and H2-temperature programmed reduction (H2-TPR) characterization techniques, the two kinds of catalysts were systematically investigated. It was found that the BET surface area and PdO dispesion degree decrease with the increase of calcinated temperature, while the peaks of CeO2 and PdO in the Raman spectroscopy, as well as the reduction temperature of Ce4+, increase with increasing calcination temperature. Consistent with the characterization results, it was found that the reactivities of toluene combustion also decrease for both catalysts. It was very interesting to note that the oxygen vacancies of the catalyst doping with La3+ into CeO2-ZrO2 solid solution is more than that of the CeO2-ZrO2 coat when calcinated at 1000℃, and the corresponding BET surface area and PdO dispersion degree are all higher than that of Pd/Ce0.8Zr0.2O2 catalyst when calcinated above 800℃. Correspondingly, the toluene combustion conversion of Pd/Ce0.8Zr0.15La0.05Oδis much higher than that of Pd/Ce0.8Zr0.2O2 catalyst calcinated at 1000℃, indicating the doping with La3+ ion greatly improve the reactivity and thermal stability of the monolithic catalyst at high calcinated temperature. Therefore the Pd/Ce0.8Zr0.15La0.05Oδmonolithic catalysts has potentially industrial applications to eliminate volatile organic compounds (VOCs).
Keywords/Search Tags:CeO2-ZrO2-La2O3, Pd, Catalytic combustion, VOCs, Monolith catalyst
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