Catalytic Supercritical Water Gasification of Soybean Straw: Effects of Catalyst Supports and Promoters

Supercritical water gasification is a hydrothermal process to gasify complex organic biomass to produce hydrogen-rich syngas. This study reports the catalytic performance and hydrogen selectivity of several Ni-based catalysts during supercritical water gasification of soybean straw. All experiments were performed at a temperature, an average biomass particle size, a feedstock/water ratio, and a residence time 500 degrees C, 0.13 mm, 1:10, and 45 min, respectively. A comprehensive screening of different support materials ranging from activated carbon (AC), carbon nanotubes (CNTs), ZrO2, Al2O3, SiO2, and Al2O3-SiO2 was performed at 10 wt % Ni loading. The effectiveness of each support in improving H-2 yield and selectivity was in the order ZrO2 > Al2O3 > AC > CNT > SiO2 > Al2O3-SiO2. The effects of adding three promoters (i.e., Na, K, and Ce) to the supported Ni/ZrO2 and Ni/Al2O3 catalysts were evaluated. In terms of H-2 yield, the performance of each promoter for Ni/ZrO2 catalysts was in the order Ce (10.9 mmol/g) > K (10.3 mmol/g) > Na (9.5 mmol/g). Cerium showed better performance in promoting H-2 yield and minimizing coke deposition on the support. The addition of K, Na, and Ce promoters elevated Ni dispersion and the metallic surface area, thus improving H-2 yields.