Study Of CO Oxidation Over PT/CuCrO Catalysts And Their Resistance To Water Vapor And Carbon Dioxide

CO catalytic oxidation has been widely applied in air purification,vehicle exhaust treatment,CO sensor and fuel cell applications,and which could also be used as a model reaction in the basic research of catalytic reactions.The study of CO catalytic oxidation has significant academic and practical values.However,under practical conditions,the reaction gases contain other components such as water vapor and CO2,and the presence of such components may exert significant influence on the catalytic belhavior:most of the catalysts suffer severe deactivation in the presence of H2O and CO2.Therefore,it is very important to develop efficient catalysts which are highly resistant to H2O and CO2.In this thesis,we prepared a series of supported Pt/CuCrO catalysts and tested for CO oxidation in the presence of H2O and CO2.These catalysts were systematically characterized by XRD,H2-TPR,BET,TEM and XPS to determine their physical/chemical properties,and the relationship between the catalyst structure and the catalytic behaviors,especially their performance in the resistance to H2O and CO2.Also,detailed kinetic studies were conducted to determine the reaction parameters such as reaction orders and activation energy,and the effects of H2O and CO2 on the reaction kinetics.The detailed contents of this thesis are as follows:1.Study of CO oxidation over Pt/CuO-CuCr2O4 catalysts and their resistance to water vapor and carbon dioxide.CuCrO supports(CuO-CuCr2O4,CuCr2O4 and CuO,respectively)were prepared using a sol-gel method and supported Pt catalysts were prepared using a incipient wetness method.The catalysts were tested for CO oxidation and their resistance to H2O and CO2.It was found that the Pt/CuO-CuCr2O4 catalyst was highly resistant to H2O and CO2,and it had better performance than that of the Pt/CuCr2O4 and Pt/CuO catalysts.However,the presence of H2O and CO2 suppressed the activity of the CuO-CuCr2O4 support.It was also found that the presence of CO2 inhibited the activity of the Pt/CuO-CuCr2O4 while the presence of H2O enhanced its activity.The kinetics on these catalysts under different conditions revealed the following facts:1.For the CuO-CuCr2O4 support,the rate expression was r=1.05×10-6Pco0.49Po20.02 under the CO + O2 condition,while the reaction order of CO increased to 0.62 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.The apparent activation energy was 52.8 kJ-mol'1 on the CuO-CuCr2O4,which was lower than the other three conditions.2.For the Pt/CuO-CuCr2O4 catalyst,the rate expression was r ?4.08×10-7PCO0.04Po20.03 under the CO + O2 condition,which implied that the lattice oxygen in the support directly participated in the reaction while the adsorption of CO on Pt surface was saturated.The reaction order of CO increased to 0.35 when CO2 or H2O was presented in the feed,suggesting the competitive adsorption of CO and H2O/CO2.The apparent activation energy was 32.3 kJ·mol-1 on the Pt/CuO-CuCr2O4,which was lower than that under the CO + O2 + CO2 condition(40.4 kJ·mol-1).However,the activation energy was lowered to 19.8 kJ·mol-1 in the presence of H2O.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 CO2 inhibited the activity but the addition of H2O improved the activity.2.Effect of calcination temperature on the performance of CO oxidation over Pt/CuCrO catalysts.The CuCrO supports were prepared by sol-gel method with different calcination temperature,and supported Pt catalysts were prepared using a incipient wetness method.The catalysts were investigated for CO oxidation and their resistance to H2O and CO2.The support calcined at 400-600? had a spinel structure(CuCr2O4),good reducibility and high amount of active oxygen species,which resulted in good performance in CO oxidation and excellent resistance to H2O and CO2.However,the support calcined at 800? had a delafossite structure(CuCrO2),low reducibility and fewer amounts of active oxygen species,which resulted in inferior performance in CO oxidation and poor resistance to H2O and CO2.The results of H2-TPR showed that the hydrogen consumption of each catalyst was obviously different,which illustrated that there was a great difference in the reducibility and the number of active oxygen species.The order of areal specific reaction rate of catalysts were Pt/CuCrO-600>Pt/CuCrO-500>Pt/CuCrO-400>Pt/CuCrO-800.By calculating the density of active oxygen species on the catalysts under low temperature,it was found that the variation of that was consistent with the change trend of the areal specific reaction rate,and the influence of active oxygen species on the reaction was further verified.The results showed that the crystalline structure of the support had significant influence on its reducibility and the amount of active oxygen species,which consequently played important roles in the catalytic performance of the catalysts.Spinel CuCr2O4 had a good reducibility and highly amount of reactive oxygen species,thereby enhancd the performance of reaction.The excellent resistance to H2O and CO2 made the catalysts had a good application prospect.