Screening of supported transition metal catalysts for hydrogen production from glucose via catalytic supercritical water gasification

In total 17 heterogeneous catalysts, with combinations of 4 transition metals (Ni, Ru, Cu and Co) and various promoters (e.g., Na, K, Mg, or Ru) supported on different materials (γ-Al2O3, ZrO2, and activated carbon (AC)), were investigated with respect to their catalytic activity and stability for H2 production from glucose via supercritical water gasification (SCWG). The experiments were carried out at 600 °C and 24 MPa in a bench-scale continuous-flow tubular reactor. Ni (in metallic form) and Ru (in both metallic and oxidized forms) supported on γ-Al2O3 exhibited very high activity and H2 selectivity among all of the catalysts investigated for a time-on-stream of 5–10 h. With Ni20/γ-Al2O3 (i.e., γ-Al2O3 with 20 wt% Ni), a H2 yield of 38.4 mol/kg glucose was achieved, approximately 20 times higher than that obtained during the blank test without catalyst (1.8 mol/kg glucose). In contrast, Cu and Co catalysts were much less effective for glucose SCWG reactions. As for the effects of catalyst support materials on activity, the following order of sequence was observed: γ-Al2O3 > ZrO2 > AC. In addition, Mg and Ru were found to be effective promoters for the Ni/γ-Al2O3 catalyst, suppressing coke and tar formation.

► Metallic form of Ni is the active site for catalyzing glucose SCWG.
► Both metallic Ru and RuO2 were comparably active for catalyzing glucose SCWG.
► γ-Al2O3 exhibited high catalytic activity for glucose SCWG.
► Mg or Ru could increase the coke resistance ability of Ni10/γ-Al2O3 in glucose SCWG.
► γ-Al2O3 was partially transformed into α-Al2O3 in the spent Ru10/γ-Al2O3 after glucose SCWG.