Pt-Re synergy in aqueous-phase reforming of glycerol and the water–gas shift reaction

Abstract

The synergy between Pt and Re in aqueous-phase reforming (APR) of glycerol and the water–gas shift (WGS) reaction was investigated for a series of carbon-supported Pt, Re, and PtRe catalysts. The overall activity of the bimetallic catalysts in APR of glycerol increases with Re content. The ratio of products obtained via C–O bond cleavage to those obtained by C–C bond cleavage also increases with Re content. H2-TPR studies and EXAFS show that Pt and PtRe catalysts are well reduced and remain so during gas- and aqueous-phase reactions. PtRe catalysts are substantially more active in C–C bond cleavage (acetaldehyde decomposition) than their monometallic counterparts, although there is no strong dependence on the Pt/Re ratio. Higher dehydration rates for PtRe alloys correlate with the increasing concentration of steam-treating-induced Brønsted acidic sites (NH3 TPD and FTIR of adsorbed pyridine). The higher glycerol conversion rate of PtRe catalysts compared to Pt mainly stems from the higher rate of CO removal from the surface by the WGS reaction. Pt and Re exhibit a very strong synergy in the gas-phase WGS reaction. Consistent with this, CO stripping voltammetry points to lower onset of CO electro-oxidation for PtRe than for Pt. It is argued that the main influence of Re is its stronger binding of oxygen species facilitating water activation, producing OH species which are involved in the WGS reaction and in C–O bond cleavage reactions.