Photothermal steam reforming of methane over silica-supported nickel catalysts with temperature gradients

Photothermal steam reforming of methane (PTSRM) is a promising catalytic technology for converting stable methane and water into hydrogen utilizing solar energy. In the present study, the photothermal catalytic activity of silica-supported nickel (Ni/SiO₂) catalysts was investigated using a gas-flow reactor under concentrated visible/near-infrared light irradiation with various experimental parameters to obtain insight into factors affecting the activity and selectivity. In the thermal SRM at 773 K in the dark, the CH₄ conversion reached near-equilibrium with all four Ni/SiO₂ catalysts, while there was a significant difference in activity between the catalysts in the PTSRM reaction under light irradiation. These results indicate that PTSRM activity was affected by both thermodynamic and kinetic aspects. The conversion-selectivity relationship revealed that the product selectivity in PTSRM was different from the values in thermal SRM in the dark and calculated thermodynamic equilibrium. We proposed that concentrated light irradiation created the highest temperature zone in the centre of the reactor and the lower temperature zone downstream, and the consecutive water gas shift reaction and CO hydrogenation occurred in the lower temperature zone, thus resulting in the characteristic product selectivity. This study shows the potential of PTSRM systems with controllable selectivity by the temperature gradients formed under concentrated sunlight irradiation.