A series of supported intermetallic Pb-Pb catalysts were prepared with the impregnation method by changing the support(silica,molecular sieve or γ-alumina)and the pore size.The chemical states of the two metals were characterized by XPS analysis,the process for producing methyl methacrylate based on the direct oxidative esterification of methacrolein with methanol in the presence of oxygen was performed in a slurry reactor with the above-mentioned catalysts.The influence of the calcination temperature and the kinds of support as well as the pore size on catalytic activity had been extensively investigated.Under the conditions of temperature at 80℃,catalyst 3.8%(ω)and the reaction time 2 h,the conversion rate of methacrolein reached 85%,the selectivity and the yield of methyl methacrylate were 90% and 76.5%,respectively.
The catalysts used for manufacturing methyl methacrylate (MMA) by two-step conversion of isobutylene via methacrolein (MAL) were studied. The selective oxidation of isobutylene to MAL was carried out in a fixed-bed flow microreactor using a series of Mo-Bi-containing catalysts and the oxidative esterification of MAL to MMA was carried out in a slurry-bed reactor using a series of palladium-containing catalysts.By means of BET and XPS, the properties of the catalysts were characterized.It was found that the performance of Mo-Bi-Co-Fe-Ce-O catalyst was improved distinctly when Cs was added for the selective oxidation of isobutylene to MAL, and the Pd 5Bi 2PbFe/CaCO 3 catalyst with the loading sequence of Pd, Pb and Bi, Fe showed the best performance for the oxidative esterification of MAL to MMA.
