Aqueous phase reforming of xylose using bimetallic Pt3-Rex/SiO2 catalysts for H2 production: Experimental and computational study

Abstract

In recent years, the aqueous phase reforming (APR) reaction using heteroge-neous catalysts has been highlighted as one of possible approaches for conver-ting nonedible biomass into hydrogen for fuel cell application. In this study,we have synthesized the rhenium (Re)-doped Pt/SiO 2 (Pt 3 Re x /SiO 2) (based onweight; x = 1, 3, 5) catalysts for enhancing the APR of organic liquid C5 sugarxylose. Our study showed that the activity of bimetallic Pt-Re catalysts towardthe APR of xylose strongly depends on the level of Re dopant. In particular, thePt3 -Re 1 /SiO2 catalyst exhibited the higher H 2 selectivity compared to the cata-lysts having the higher amount of Re dopant (Pt 3 -Re 2 /SiO 2 and Pt 3 -Re 3/SiO 2 ).Furthermore, the oxygen state of ReOx could be modified by changing reduc-tion temperature. The measured hydrogen selectivity and reaction rate couldbe enhanced when the catalyst was reduced at higher temperature. Especially,the Pt 3 -Re 1/SiO2 catalyst reduced at 500 C under 10 vol% H 2 flow exhibitedhigh catalytic performances close to the theoretical values in the initial stage ofthe 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 metal-lic state Pt and Re in Pt 3 Re alloy phase and low oxidation state Re (Re 3+) ele-ment is responsible for the improved H 2 selectivity in Pt 3-Re1 /SiO 2 catalystreduced at 500 C. In addition, the density functional theory calculation alsopredicted that the surface exposure of Pt and Re atoms (rather than oxidizedReOx ) can boost the first dehydrogenation of xylose, which is in a good agreement with the experimental observation. This study can provide the opti-mal oxidation level of Re and Pt in the bimetallic Pt-Re catalyst to efficientlyobtain hydrogen from xylose via APR reaction.