Elucidation of the Roles of Re in Aqueous-Phase Reforming of Glycerol over Pt–Re/C Catalysts

Abstract

We report the investigation of surface properties of Pt/C and Pt–Re/C catalysts using in situ spectroscopic tools and a fundamental understanding of their catalytic performances in glycerol aqueous-phase reforming (APR). We found that adding Re to Pt/C improves its activity significantly, which is consistent with our previous observation in glycerol steam reforming. However, the difference in reaction selectivity is much more pronounced in APR. Compared to Pt/C, Pt–Re/C yielded significantly more liquid products, while the selectivity to H2 and CO2 decreased by more than 40%. In operando X-ray absorption spectroscopy and attenuated total reflectance infrared (ATR-IR) with in situ capability as well as Raman spectroscopy were employed to investigate the catalyst surface properties and the roles of Re. In operando X-ray absorption fine structure shows significant oxidation of Re, and ATR-IR of adsorbed pyridine revealed the formation of acid sites on PtRe after hot liquid water treatment. Additionally, ATR-IR using CO as a probe molecule demonstrated that desorption of CO from the Pt–Re/C surface is more facile than that from Pt/C in the aqueous phase. We propose that well-dispersed Re oxide species in the proximity of Pt work as the active sites, providing both metal and acid functionalities, while the terminal Re–O moiety has little contribution to the overall reactivity as evidenced by Raman spectroscopy.