Au@Snβ zeolite as stable and active catalyst for the conversion of glycerol to methyl lactate

Au/Sn-zeolite catalysts showed high activity for selective conversion of glycerol to methyl lactate, but suffered from poor stability under the reaction conditions in our previous report (ACS Catal. 2017, 7, 7274). Encapsulation of Au nanoparticles within zeolite is a promising strategy to enhance their stability in catalytic reaction. Herein, one-pot synthesis of Au@Sn beta was achieved by a mercaptosilane-assisted hydrothermal synthesis method. The protocol involves crystallization of Sn beta synthesis gels around coordinated Au precursors, resulting in Sn beta framework constraining Au coordination complexes. The confinement of small (similar to 2.89 nm) and uniform Au particles within Sn beta was achieved. The bifunctional catalyst composed of oxidative sites (Au) and Lewis acid sites (Sn) gave 77.3 % methyl lactate (MLA) yield from the base-free selective conversion of glycerol (GLY). The TOF value of Au@Sn beta was higher than that of Au/Sn-zeolite in our previous report. Moreover, the special structure protects Au nanoparticles from sintering or agglomeration and improves the stability and recyclability in selective oxidation of GLY to MLA.