Aqueous phase reforming of xylose using bimetallic Pt-3-Re-x/SiO2 catalysts for H-2 production: Experimental and computational study

Abstract

In recent years, the aqueous phase reforming (APR) reaction using heterogeneous catalysts has been highlighted as one of possible approaches for converting nonedible biomass into hydrogen for fuel cell application. In this study, we have synthesized the rhenium (Re)-doped Pt/SiO2 (Pt3Rex/SiO2) (based on weight; x = 1, 3, 5) catalysts for enhancing the APR of organic liquid C5 sugar xylose. Our study showed that the activity of bimetallic Pt-Re catalysts toward the APR of xylose strongly depends on the level of Re dopant. In particular, the Pt-3-Re-1/SiO2 catalyst exhibited the higher H-2 selectivity compared to the catalysts having the higher amount of Re dopant (Pt-3-Re-2/SiO2 and Pt-3-Re-3/SiO2). Furthermore, the oxygen state of ReOx could be modified by changing reduction temperature. The measured hydrogen selectivity and reaction rate could be enhanced when the catalyst was reduced at higher temperature. Especially, the Pt-3-Re-1/SiO2 catalyst reduced at 500 degrees C under 10 vol% H-2 flow exhibited high catalytic performances close to the theoretical values in the initial stage of the reaction, but its activity was gradually reduced by re-oxidation of ReOx. From the various analysis results, we can figure out that the presence of metallic state Pt and Re in Pt3Re alloy phase and low oxidation state Re (Re3+) element is responsible for the improved H-2 selectivity in Pt-3-Re-1/SiO2 catalyst reduced at 500 degrees C. In addition, the density functional theory calculation also predicted that the surface exposure of Pt and Re atoms (rather than oxidized ReOx) can boost the first dehydrogenation of xylose, which is in a good agreement with the experimental observation. This study can provide the optimal oxidation level of Re and Pt in the bimetallic Pt-Re catalyst to efficiently obtain hydrogen from xylose via APR reaction.