Accelerated synthesis of Sn-Beta with less silanols by alkaline (earth) salt for efficient transformation of glucose to methyl lactate

Abstract

Sn-Beta zeolite is an excellent catalyst for the transformation of biomass derived carbohydrates. However, the long synthesis time restricted its application. Here, alkaline (earth) salt was used as promoter to accelerate the crystallization of Sn-Beta. Different alkaline (earth) salts and the amount of MgCl2 were investigated. The properties of the synthesized samples were characterized by various techniques and compared with Sn-Beta, and the catalytic performance was investigated for the conversion of glucose to methyl lactate (MLA). The results indicate that a small amount of alkaline (earth) salt, especially MgCl2, promoted dramatically the crystallization of Sn-Beta. The full crystallization time was shortened from 15 d to 5 d with the aid of MgCl2 (nMg/nSn of 1.0) for Sn-Beta with nSi/nSn of 100. Sn4+ cations were incorporated into the framework sites, while Mg2+ cations replaced the protons of silanol defects. Mg–Sn-Beta with strong Lewis acid sites and less silanols showed high activity and selectivity for glucose conversion to MLA. The yield of MLA is 20% over the fully crystallized Sn-Beta at 120 °C for 15 h and glucose concentration of 3.1 wt%, which increased significantly to 44% over the fully crystallized 1 Mg–Sn-Beta. Furthermore, Mg–Sn-Beta is stable and recyclable.