Catalytic performance of MCM-41 with different pore sizes in selected liquid phase reactions

초록

A series of MCM-41 with pore diameters in the 20-90 Å range were prepared and the effects of pore size on liquid phase reactions of epoxidation, etherification, and esterification were investigated after Ti-grafting, immobilization of Mn-salen complex, and monolayer adsorption of SO3H were performed on the host materials, respectively. Amount of functionalized species increased with the pore diameters of MCM-41, but it leveled off after a thresh hold pore size is achieved. MCM-41 with pore diameter of ca. 56 Å was recommended to obtain high concentration of grafted species with good catalytic performances. In cyclohexene epoxidation, conversion showed linear relationship with Ti-contents of the catalyst, which proved to be a primary factor governing the reaction rather than diffusion effect. For MCM-41 immobilized with Mn-salen complexes, active site isolation in high surface coverage was required for good catalytic performances. MCM-41 with enlarged pores was again better for larger amount of thiol group to be attached to the mesopores, but uniform surface property/shape seems also required to promote the formation of a monolayer-type coated material. Esterification of 1-propanol with hexanoic acid was best catalyzed by the acidity of the sulfone-functionalized MCM-41 materials synthesized after 12 h oxidation treatment of the thiol-grafted MCM-41.