Correlation of Pt–Re surface properties with reaction pathways for the aqueous-phase reforming of glycerol

The surface properties of Pt–Re catalytic nanoparticles supported on carbon following exposure to a hydrogen reducing environment and subsequent hydrothermal conditions have been studied using in situ X-ray photoelectron spectroscopy (XPS) and ammonia temperature-programmed desorption (TPD). These properties have been correlated with the catalyst selectivity for the aqueous-phase reforming of glycerol. We show that Pt in reduced Pt–Re/C becomes electron deficient, and a fraction of the Re becomes oxidized when the catalyst is subsequently exposed to hydrothermal reaction conditions. Oxidation of Pt–Re generates surface acidity, which drastically affects the reaction pathways. The acid site concentration, but not acid site strength, increases with Re loading. This acidity increase with Re addition favors C–O over C–C cleavage, which results in higher selectivity to liquid products and alkanes at the expense of hydrogen selectivity. We propose a model for the Pt–Re active site and the origin of acidity enhanced by the addition of Re.

The major reaction pathways for aqueous-phase reforming of glycerol show the dependence of product selectivity on C–C bond cleavage (metal site-based) vs. C–O bond cleavage (acid site-based).Figure optionsDownload high-quality image (66 K)Download as PowerPoint slideHighlights
► Addition of Re to Pt/C results in a change in product selectivity, consistent with an increase in C–O bond cleavage reactions.
► A Pt–Re alloy forms on initial catalyst reduction, but some Re oxidizes under aqueous-phase reforming conditions.
► Oxidation of Re results in generation of acidity, as verified by NH3 TPD.
► Acidity amount correlates with Re concentration, and infrared studies suggest formation of Brønsted acid sites.