Bifunctional Solid Lewis Acid–Base Catalysts for Efficient Conversion of the Glucose–Xylose Mixture to Methyl Lactate

Sugars produced from lignocellulose hydrolyzate are usually a mixture, of which glucose and xylose are the most abundant. Herein, a bifunctional solid catalyst (Mg-Sn-Beta zeolite) with Lewis (L) acidity and L basicity is developed, which can efficiently catalyze the glucose–xylose mixture to methyl lactate (MLA). This avoids the economic cost and cumbersome operation caused by separating mixed sugars. The retro-aldol condensation and aldol condensation are two major steps in converting glucose and/or xylose to MLA. L acid sites and L base sites in Mg-Sn-Beta zeolite are favorable for the above two steps. 1Mg-Sn-Beta-x and yMg-Sn-Beta-100 with different contents of L acid sites and L base sites were characterized via various techniques. In the conversion of glucose–xylose mixture to MLA, a considerable yield (52%) was obtained over 2Mg-Sn-Beta-100 compared with that on Sn-Beta-100 (25%). Besides, 2Mg-Sn-Beta-100 exhibited excellent stability and reusability during five reaction runs.