DEVELOPMENT OF NOVEL CATALYSTS FOR HYDROGEN GAS PRODUCTION FROM BIOMASS COMPOUNDS

Hydrothermal biomass gasification technologies (sub- and supercritical water gasification and aqueous-phase reforming) have considerable economic, environmental, and technical advantages over other energy-extensive technologies (e.g. natural gas reforming) for hydrogen gas production. However, lack of economically feasible and highly active catalysts is a main challenge that impedes upscaling of these technologies for hydrogen gas production. The goal of this study was to develop innovative, economically feasible and active heterogeneous supported metal catalysts for hydrothermal processes for producing hydrogen gas from biomass-derived compounds. Because of its stable structure and chemical inertness, graphene was used as catalyst support. Graphene supported metal catalysts were prepared using different Pt precursors (H2PtCl6·6H2O, PtBr2, PtCl2, and PtI2) and different metals in monometallic (Pt, Ni and W) and bimetallic (Pt-Ni and Pt-W) combinations for hydrothermal gasification of biomass compounds. The catalysts were prepared by wet impregnation and ultrasound-assisted wet impregnation for comparison. Sequential reduction methods (first chemical reduction with NaBH4 then thermal reduction with heating at 300 °C under nitrogen flow) were applied to reduce metal precursors on the support. Catalytic activity of the catalysts were tested by aqueous-phase reforming (APR) as a low temperature hydrothermal gasification technology. Glucose as simple biomass compound was used as feed in APR process. It was found that the size and distribution of metal particles on the graphene support were highly dependent on the metal type and the metal precursor used in the preparation of the catalysts. The 8 wt.% of metal loading was successfully achieved in all catalysts when ultrasound-assisted wet impregnation deposition method was used. When catalyst was prepared using PtCl2 precursor, the sizes and distributions of Pt particles on graphene were relatively small and uniform with narrow dispersion compared to the catalysts prepared with PtI2, PtBr2 and H2PtCl2 precursors. Deposition of W particles on graphene exhibited better results than Ni catalysts in terms of metal particle size and distribution. APR results showed that use of different Pt precursor did not change catalytic activity of Pt/graphene catalysts in terms of total gas mixture and hydrogen produced in APR process if ultrasonication was used in wet impregnation process. Combination of Ni and W metals with Pt showed positive synergy and the catalytic performance of bimetallic catalysts was significantly enhanced. Advisors: Sibel Irmak and Mark Wilkin