(641c) Aqueous Phase Reforming of Glycerol Over Pt/Al2O3

Aqueous phase reforming is a promising metal catalyzed process for the production of hydrogen from biorenewable feedstocks. In this reaction biomass derived oxygenates are decomposed to surface bound carbon monoxide and hydrogen followed by the water-gas shift reaction. Further development of APR reforming catalysts would greatly benefit from fundamental insight on how the composition and structure of supported metal catalysts affect each of the elementary steps involved.

The present study provides such insight by in-situ ATR-IR spectroscopy. Even at room temperature Pt/Al₂O₃ converts glycerol to surface bound carbon monoxide and hydrogen. CO can be bound on atop or bridging metal sites. The maximum surface concentration and rate of formation of these CO species strongly depend on the presence of co-adsorbed species, such as hydrogen and non-reactive oxygenates. In particular, more linearly bound CO and less bridging CO are formed in the presence of other strongly adsorbed surface species. The rate of CO formation also varies notably for different oxygenate feedstock, and side reactions become more relevant with increasing size of the oxygenate molecule.

In addition to surface reaction of glycerol on Pt, surface interactions with the alumina support require attention. In an aqueous environment glycerol competes with water molecules for adsorption sites on polar supports like alumina. However, chemisorbed alkoxy species are formed at elevated temperature or in vacuum. In particular, multidentate alkoxy species are remarkably stable.