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-Al 2O 3, ZrO 2, and activated carbon (AC)), were investigated with respect to their catalytic activity and stability for H 2 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-Al 2O 3 exhibited very high activity and H 2 selectivity among all of the catalysts investigated for a time-on-stream of 5–10 h. With Ni20/γ-Al 2O 3 (i.e., γ-Al 2O 3 with 20 wt% Ni), a H 2 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-Al 2O 3 > ZrO 2 > AC. In addition, Mg and Ru were found to be effective promoters for the Ni/γ-Al 2O 3 catalyst, suppressing coke and tar formation. ► Metallic form of Ni is the active site for catalyzing glucose SCWG. ► Both metallic Ru and RuO 2 were comparably active for catalyzing glucose SCWG. ► γ-Al 2O 3 exhibited high catalytic activity for glucose SCWG. ► Mg or Ru could increase the coke resistance ability of Ni10/γ-Al 2O 3 in glucose SCWG. ► γ-Al 2O 3 was partially transformed into α-Al 2O 3 in the spent Ru10/γ-Al 2O 3 after glucose SCWG.