LAUSR

The one-step conversion of α-keto aldehydes to α-hydroxy carboxylic acids and their derivatives using solid acids is of great appeal in biomass utilization. In this work, ordered mesoporous zirconium oxophosphate (ZrPO) catalysts with tunable acidity were prepared and their catalytic performance was evaluated using phenylglyoxal (PG) conversion to ethyl mandelate (EM). The roles of Lewis acid sites (LAS) and Bronsted acid sites (BAS) of ZrPO were investigated by kinetic studies of PG conversion combined with temperature-programmed desorption of ammonia (NH3-TPD) and solid-state NMR characterizations. It is found that the ratio of LAS to BAS on the ZrPO plays a dominant role in this reaction. ZrPO-0.75-500, with a LAS/BAS ratio of 2.1, was found to be the best catalyst. The reaction pathways, i.e., the direct isomerization of PG to EM by LAS and via the formation of an intermediate hemiacetal by BAS, are therefore proposed. Moreover, the effect of water on the catalytic activity was studied. A moderate amo...