Catalytic Supercritical Water Gasification of Soybean Straw: Effects of Catalyst Supports and Promoters
Jude A. Okolie, Alivia Mukherjee, Sonil Nanda, Ajay K. Dalai, Janusz A. Koziński
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.