Tuning Brønsted/Lewis Acid Site Ratios via Ammonia Modulation for Selective Conversion of Glycerol to 1,3-Propanediol or Solketal

In this study, two different ferric hydroxyphosphate (FHP and FHP-B) catalysts, synthesized by the same procedure with or without the addition of aqueous ammonia have shown excellent performance in the hydrogenolysis of glycerol to 1,3-propanediol (1,3-PDO) (conversion of glycerol: 60.7%; selectivity of 1,3-PDO: 87.9%) and acetalization of glycerol to solketal (conversion of glycerol: 94.9%; solketal selectivity: 98.3%). Simultaneously converting glycerol to two high-value-added chemicals is of great significance. Meanwhile, the two catalysts are characterized by a series of instruments, and the results show that the addition of aqueous ammonia alters the concentration of Brønsted and Lewis acidic sites of the catalysts, thus allowing them to attack different hydroxyl groups on glycerol. The Brønsted acid sites (BAS) of the FHP catalyst without the addition of aqueous ammonia were more selective for the breaking of the 2°-OH bond, whereas the FHP-B catalyst, due to the presence of aqueous ammonia, converted some BAS to Lewis acid sites (LAS) during the synthesis process. A large amount of LAS was inclined to attack glycerol's 1°-OH bond, which is more favorable for the condensation reaction of glycerol and acetone. This finding innovatively provides a new strategy for the catalyst synthesis and a new perspective on reaction mechanism research.