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•Seven heterogeneous catalysts were studied and compared on sewage sludge gasification in near and supercritical water.•Maximum carbon gasification efficiency and hydrogen yield was 90.1% and 18.13 mol /kg dry sludge at 450 °C.•Raney-nickel with Mo component exhibited better catalytic activity in near and supercritical water.•RNi-Mo2 had the best catalytic activity for gasification in near and supercritical water.•Spongy structure、larger specific area and better pore distribution of RNi-Mo2 were important for gasification.
Catalytic gasification of activated sewage sludge in nearcritical and supercritical water was researched in batch reactor. Different types of commercial catalysts including Ru/C, Raney-iron, Raney-cobalt and different types of Raney-nickel were used. Effects of catalyst type, reaction temperature (350 °C, 400 °C and 450 °C), residence time (5 min–25 min) and catalyst amount were investigated. Temperature was positive for hydrogen yield and Raney-nickel with Mo metal had better catalytic activity. The addition of Raney-nickel-Mo2 promoted the formation of hydrogen better. At 450 °C and 25 min, the maximum hydrogen yield reached to 18.13 mol/kg dry sludge with 1.4 g Raney-nickel-Mo2 catalyst/g dry sludge, and the maximum LHV, GE, CE and HYP achieved 14.3 MJ/Nm3, 92%, 90.1% and 63.5 mol/kg dry sludge respectively. Although the compositions of two Raney-nickel with Mo were similar, Raney-nickel-Mo2 had better catalytic activity because it not only had the spongy structure but also it had larger specific area and better pore space concentration distribution.