Supercritical water gasification of glucose using bimetallic aerogel Ru-Ni-Al2O3 catalyst for H2 production

Hydrogen production from biomass using supercritical water gasification (SCWG) is gaining considerable attention as a sustainable source for emerging energy needs. A significant problem with SCWG is the low activity of conventional catalysts with simultaneous graphitic coke formation on the catalyst surface. In this contribution, novel bimetallic nickel-ruthenium supported on alumina catalysts were synthesized via a sol-gel process followed by scCO2 drying (aerogel catalyst). In order to investigate the effect of both Ru and the drying step, both supercritical and conventional drying (xerogel catalyst) were compared with and without Ru. All catalyst types were examined for glucose gasification in supercritical water using a 600 cm3 batch reactor from 400 to 500 °C at 25 to 35 MPa. The fresh and spent catalysts were then characterized by various physico-chemical techniques to understand the role of Ru and the deactivation mechanism. Ru-Ni-Al2O3 aerogel catalyst reduced graphitic coke formation, significantly enhancing H2 formation while also increasing the carbon gasification efficiency (CGE) and total organic carbon (TOC) destruction, respectively. H2 yield was increased 1.7 times higher for Ru-Ni-Al2O3 aerogel compared to the xerogel. Ni-Al2O3 aerogel and impregnated catalyst provided 1.26 and 1.55 times lower H2 yield compared to Ru-Ni-Al2O3 aerogel catalyst. This is attributed to the Ru-Ni-Al2O3 aerogel catalyst having a higher BET surface area as well as larger pore volume, smaller active metal crystallite sizes, and a higher degree of active metal dispersion.