Oxidative Dehydration of Glycerol to Acrylic Acid over Vanadium-Substituted Cesium Salts of Keggin-Type Heteropolyacids

Acrylic acid is one of the most desired products from bioglycerol. In this work, we demonstrated that Keggin-type heteropoly compounds (HPCs) act as efficient bifunctional catalysts for the one-step conversion of glycerol to acrylic acid in gas phase. This is the first example of HPCs as catalysts for selective conversion of glycerol to acrylic acid. It was found that introduction of vanadium species into the secondary structure of the cesium salts of H3PMo12O40 and H3PW12O40 heteropolyacids is beneficial for acrylic acid formation. The combination of H0.1Cs2.5(VO)0.2PMo12O40 and H0.1Cs2.5(VO)0.2PW12O40 as solid solutions resulted in variations in the oxidization ability and surface acidity of the catalysts and, consequently, notably improved selectivity for acrylic acid. Up to 60% yield to acrylic acid was achieved over the catalyst with the formula of H0.1Cs2.5(VO)0.2(PMo12O40)0.25(PW12O40)0.75. The catalyst also showed good resistance to coke deposition and long-term stability due to the salt feature. It is deduced that the synergism between the Keggin anions and the cesium/vanadium entities at the secondary structure determined the overall catalyst performance.