Formation of Ordered Mesoporous MgO with Tunable Pore Diameter and Its Application As Excellent Alkaline Catalyst in Baeyer−Villiger Oxidation

Abstract

Highly ordered mesoporous MgO catalysts with tunable pore size distribution and fairly good alkaline property were successfully obtained by a double replication procedure. Small-angle XRD, TEM, and nitrogen adsorption and desorption results show that these mesoporous MgO materials possess a highly ordered 2D hexagonal mesostructure with tunable pore diameter that is obtained using different hydrothermal temperature derived SBA-15 and CNK-3 carbon as templates. The alkaline density was determined for all samples from the technique of temperature-programmed desorption of CO2 and FT-IR, and the mesoporous MgO with large pore diameter shows more basic sites than the reference bulk one. Such mesoporous MgO materials have been successfully used as base catalysts in the Baeyer−Villiger oxidation of cyclic ketones to the corresponding lactones. 100% adamantanone conversion and >99% lactone selectivity were obtained over mesoporous MgO-373. The pore diameter has slight influence on the conversion of ketones, since the average pore diameters of mesoporous MgO are large enough to allow the reactants free access to the active sites. In terms of the proposed mechanism, the enhanced medium alkaline properties will be more favorable for the attack by hydrogen peroxide to form a hydroperoxide and percarbonic oxide, and in turn enhancing the catalytic activity. In addition, the higher surface area and large pore volume are attributed to the higher activity of mesoporous MgO-373 than the others, signifying the promising potential applications of these mesoporous MgO materials in alkaline catalysis.