CO Oxidation Over Pt Catalysts And Their Resistance To Water And Carbon Dioxide

Carbon monoxide is a the colorless,odorless and harmful gases.The fossil fuel combustion,the chemical industry,and automobile cause a large amount of CO emissions and become a serious environmental problem.Therefore,the abatement of CO is urgent.Among various methods,low-temperature CO catalytic oxidation is the most economical and effective way to eliminate CO,which attracts much attention in catalysis field.Noble metal catalysts are very active and stable under dry reaction conditions,however,the presence of high concentrations of impurities such as H₂O and CO₂ under practical conditions usually causes severe catalyst deactivation.Therefore,it is very important to develop highly effective catalysts which are resistant to H₂O and CO₂.In this thesis,we have conducted CO oxidation over Pt supported on reducible oxides.The main goals of the work include:1.To investigate the effect of the surface properties of the supports on the performance of CO oxidation.2.To investigate the resistance to H₂O and CO₂ over the Pt catalysts in CO oxidation and the reaction mechanisms.3.To investigate the effect of crystal structure of the support on the catalytic performance of CO oxidation and the resistance to H₂O and CO₂.The findings of this work provide better understanding of the synergistic effect of metal and support on CO oxidation and resistance to H₂O and CO₂,which might be helpful for the design of highly efficient catalysts for CO oxidation under practical conditions.This paper mainly includes the following contents:1.CO oxidation over Pt/MO_x?M=Ni,Fe,Co,Ce?catalysts and their resistance to water vapor and carbon dioxide.Supported Pt catalysts?1Pt/Ni O,1Pt/FeOx,1Pt/Co3O4 and 1Pt/CeO2?were tested for CO oxidation under different reaction conditions.It was found that the addition of CO₂ in the reaction atmosphere resulting in catalyst deactivation.The addition of H₂O inhibited the activity of the Pt/CeO2 catalyst,but promoted the activity of the 1Pt/FeOx,1Pt/NiO and 1Pt/Co₃O₄ catalysts.For the 1Pt/FeO_x and 1Pt/CeO₂ catalysts,detailed kinetic results and staged reaction indicated that although the addition of H₂O formed a competitive adsorption with CO on both catalysts,on 1Pt/FeOx catalyst,the hydroxyl group formed by the dissociation of H₂O on the 1Pt/FeOx catalyst surface was more likely to react with CO,which opens a new reaction path and thus improved the the activity.Meanwhile,H₂O can decompose carbonate species and sustain the catalyst stability.2.The effect of H₂O on the performance of CO oxidation over Pt/Fe Ox catalysts.CO oxidation was performed over various 1Pt/FeOx catalysts with the FeOx support calcined at different temperatures.It was found that the activities of the catalysts under CO+O₂ condition followed an order of 1Pt/FeO_x-300>1Pt/FeOx-400>1Pt/FeOx-500>1Pt/FeOx-600.In the presence of H₂O,compared with the activity in the dry atmosphere?CO+O₂?,the order of the promotion was1Pt/FeOx-400>1Pt/FeOx-300>1Pt/FeOx-500>1Pt/FeOx-600.The most pronounced improvement was observed on the 1Pt/FeOx-400 catalyst.Characterizations of the catalyst revealed that the FeOx-400 support contained a mixture of?-Fe2O3 and?-Fe2O3,which possessed better low-temperature reducibility and higher content of Fe²⁺species.The XPS results indicated that the addition of H₂O could maintain the presence of Fe²⁺,which may provide new sites for activation of O₂ molecules and thus high reactivity.The kinetics experiments showed that the addition of H₂O may trigger a new reaction pathway.