Shengqiang Zhou,Tianliang Lu,Lipeng Zhou,Xiaomei Yang
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@Snβ was achieved by a mercaptosilane-assisted hydrothermal synthesis method. The protocol involves crystallization of Snβ synthesis gels around coordinated Au precursors, resulting in Snβ framework constraining Au coordination complexes. The confinement of small (∼2.89 nm) and uniform Au particles within Snβ 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@Snβ 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.
Bo Tang,Di Wang,Ang Li,Hui-Min Tang,En-Cui Yang,Weili Dai
Herein, core-shell structured Snβ@mesosilica (MS) composite was constructed by oriented assembly of mesoporous silica on microporous Snβ zeolite . The mesoporous channels in the shell were verified vertically aligned to the Snβ core, rendering sufficient mass transfer between the shell and core. The resultant Snβ@MS was thereafter employed as the scaffolds for anchoring Au nanoparticles to develop a bifunctional Au/Snβ@MS catalyst for one-pot base-free conversion of glycerol to methyl lactate (ML), which is regarded as a promising and sustainable route to ML production. Under optimum reaction conditions, a remarkable activity with 98.2% glycerol conversion and 91.9% ML selectivity was achieved. More importantly, the introduction of mesoporous silica shell can efficiently modify the Lewis/Brønsted acid ratio of Snβ@MS, thus inhibit the side reactions. While the confinement effects could protect the highly dispersed Au nanoparticles against sintering. Accordingly, a high stability and recyclability was achieved over the Au/Snβ@MS catalyst.
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