Study Of CO Oxidation Over Pt-based Catalysts And Their Resistance To Water Vapor And Cabon Dioxide

Carbon monoxide(CO)is mainly generated from vehicle exhaust,industrial waste gas and daily life emissions,which is greatly harmful to human health.Catalytic CO oxidation is an efficient way to the CO abatement and this reaction is also an excellent model reaction to investigate the catalyst structure-catalytic performance relationship.However,under practical reaction conditions,the feed gases contain other components such as water vapor and CO2,which can cause severe catalyst deactivation.Therefore,the development of catalyst systems with good resistance to H2O and CO2 is of great importance.In this thesis,we prepared a series of supported Pt-based catalysts and tested for CO oxidation in the presence of H2O and CO2.The structure,chemical properties of the catalysts were systematically analyzed by various characterizations,and the effects of H2O and CO2 on the catalytic behaviors were investigated by kinetics studies.The detailed contents of this thesis are as follows:1.Effect of MnOx promotion on CO oxidation over Pt/CeZrO2 catalysts under water vapor and CO2 conditionsA series of supported Pt/CeZrO2 catalysts were prepared by an impregnation method and the effect of different metal oxide promoters on the CO oxidation was investigated.It was found that the addition of MnOx could effectively enhance the activity.Also,the effect of MnOx content on the catalytic activity and the resistance of H2O and CO2 was investigated in detail.The results showed that the activity of the Pt/MnOx/CeZrO2 catalyst first increased and decreases with increasing MnOx content in the catalyst,with a maximum obtained on the catalyst with a MnOx content of 0.5wt.%.Various characterization results revealed that the addition of MnOx improved the catalyst reducibility of the catalysts and thus the activity.The addition of H2O vapor and CO2 in the feed gases suppressed the activity of the Pt/CeZrO2 catalyst,while the MnOx promotion in the catalyst could effectively alleviate such suppression.Kinetic study revealed that for the Pt/CeZrO2 catalyst,the reaction order of CO increased from 0.47 to 0.71 and 0.67 with the H2O vapor and CO2,respectively,which suggested that the decline of activity might be due to the competative adsorption of H2O and CO2 with CO on the catalyst surface.In contrast,for the Pt/0.5MnOx/CeZrO2 catalyst,the reaction order of CO increased from 0.40 to 0.56 and 0.50 with the H2O vapor and CO2,respectively.This observation implied that the addition of MnOx could suppress the competative adsorption of H2O and CO2 with CO on the catalyst surface,which could well explain the good resistance of H2O and CO2 of the Pt/0.5MnOx/CeZrO2 catalyst.2.Study of CO oxidation over Pt/MCrO catalysts and their resistance to water vapor and CO2.A series of MCrO(M = Ni,Mn,Zn,Co)composite supports were prepared by a sol-gel method,and supported Pt-based catalysts were prepared by an impregnation method.The effects of M species on the CO oxidation and their resistance to H2O and CO2 were investigated.It was found that the Pt/NiCrO and Pt/MnCrO catalysts were highly resistant to H2O and CO2,and they had better performance than those of the Pt/ZnCrO and Pt/CoCrO catalysts.However,the presence of H2O and CO2 suppressed the activity of the Pt/ZnCrO and Pt/CoCrO catalysts.It was also found that the presence of CO2 inhibited the activities of the Pt/NiCrO and Pt/MnCrO catalysts while the presence of H2O enhanced their activities.The kinetics on Pt/ZnCrO and Pt/NiCrO catalysts under different conditions revealed the following facts:For the Pt/ZnCrO catalyst,the rate expression was r = 5.58×10-7Pco035Po20.04 under the CO +O2 condition with an activation energy of 35.3 kJ·mol-1,while the reaction order of CO increased to 0.54,0.45 respectively when CO2 or H2O was presented in the feed but the reaction order of O2 remained unchanged.These results implied that the lattice oxygen in the support directly participated in the reaction,and the adsorption of CO2 or H2O competed with that of CO,which weakened the coverage of the latter.Meanwhile,the activation energies on the presence of H2O and CO2 increased to 44.7 and 42.5 kJ·mol-1,respectively.For the Pt/NiCrO catalyst,the rate expression was r =4.44×10-7Pcoo0.43Po20.04 and the apparent activation energy was 43.7 kJ-mol'1 under the CO + O2 condition.The reaction order of CO increased to 0.56,0.51 respectively while the reaction order of O2 remained unchanged when CO2 or H2O was presented in the feed,but the the activation energy of the reaction decreased to 23.9 kJ-mol-1 after the H2O was added to the reactant gas.These results suggested that although the presence of CO2 and H2O lowered the coverage of adsorbed CO,their roles in the reaction were completely different,that is,the addition of H2O reduced the activation energy of the reaction that improved the activity but the addition of CO2 inhibited the activity.