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

Abstract

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 °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 H₂ 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 H₂ 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 H₂ 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 H₂ yields.