Insight into the basic strength-dependent catalytic performance in aqueous phase oxidation of glycerol to glyceric acid

Abstract

Fundamental understanding of basic site of supported metal catalysts is highly desirable for aqueous phase oxidation of alcohols without adding extra alkali. Herein, nanoscale alkaline earth metals doped Pt/M−MCM−41 catalysts (M = Mg, Ca, Sr and Ba) were prepared for the aqueous phase oxidation of glycerol to glyceric acid in base-free medium. By establishing the correlation between basic active site and catalytic performance, it is found that catalytic activity increases almost linearly with the strength of basic sites, and excessively strong basic sites are not conducive to the improvement of glyceric acid selectivity. Multi-characterizations revealed that strong basic sites generated by alkaline earth metal oxides (especially MgO and CaO) could induce the enhanced electronic transfer ability, the modified reduction properties of Pt and abundant surface oxygen vacancies in the Pt/M−MCM−41 catalysts. Moreover, reaction kinetics demonstrated that the addition of alkaline earth metal oxides (e.g. CaO) could promote the activation of primary hydroxyl group and C-H bond, resulting in the excellent catalytic performance. In addition, as the representative of the optimal solid base catalysts, the Pt/Ca-MCM-41 (70) catalyst also exhibits record high turnover frequency (TOF) values for the oxidation of glucose (9623.0 h−1) and xylose (4561.0 h−1) to corresponding carboxylic acids.