Impact of redox properties on dehydration of glycerol to acrolein over heteropolyacids assessed by operando-EPR spectroscopy

H3PMo12O40·xH2O and H4PVMo11O40·xH2O with Keggin structure were supported on SiO2–Al2O3 carriers with Si/Al = 0.21 and 0.32 as well as on Al–MCM-41 (Si/Al = 10), characterized and monitored by operando-EPR in the dehydration of glycerol to acrolein at 553 K using feed streams of glycerol/N2/H2O/O2 = 1/14.1/36.8/0.68 or 1/14.1/36.8/0. Upon deposition on the supports, the Keggin anions are degraded into fragments containing about 3–6 metal ions. Both the presence of vanadium as well as small amounts of O2 in the feed keeps the Mo species in a highly oxidized state. This diminishes slightly the acrolein selectivity but also the condensation degree of the carbon deposits which might favour catalyst stability.

Vanadium ions doped into supported H3PMo12O40 and traces of O2 in the feed suppress reduction of Mo6+ to Mo5+ by preferential formation of V4+. This leads to more active and stable catalysts, since it hinders the formation of highly condensed and deactivating coke species.Figure optionsDownload high-quality image (122 K)Download as PowerPoint slide