Conversion of dihydroxyacetone to methyl lactate catalyzed by highly active hierarchical Sn-USY at room temperature

Hierarchical Sn-USY zeolites were prepared by the post-synthesis method via dealumination of H-USY zeolite with nitric acid and solid-state ion-exchange with SnCl4. High concentration of nitric acid was favorable for removal of framework Al and the following Sn incorporation. The physicochemical properties of Sn-USY zeolites were characterized by various techniques. Sn was incorporated into the framework site which created Lewis acid sites. Meanwhile, the abundant mesopores generated by acid treatment were preserved after Sn incorporation. The prepared hierarchical Sn-USY zeolites were used to catalyze the conversion of 1,3-dihydroxyacetone (DHA) to methyl lactate (MLA) in methanol. It is found that the hierarchical Sn-USY zeolites are highly active and selective for this reaction. At ambient temperature (25-40 degrees C), DHA was completely transformed with more than 95% MLA yield. Moreover, the hierarchical Sn-USY zeolites are recyclable and reusable at least five times without significant loss of activity and selectivity.