Effects of K doping over ordered mesoporous nickel-alumina catalysts on toluene steam reforming

Abstract

Nickel-based catalysts have been broadly studied for the steam reforming of coal/biomass tar due to their inexpensiveness and good activity. Nevertheless, their industrial application has long been restricted by the deactivation induced by carbon deposition and Ni sintering in the reforming process. Herein, ordered mesoporous nickel-alumina catalysts with varying K contents were prepared. Their performance in steam reforming of toluene as a model compound of tar was evaluated to reveal the effects of K doping. Among them, the catalyst with 2 wt% K loading displayed the best catalytic activity and stability. Experimental and theoretical calculation results suggested that K doping enhances the water adsorption capability of the catalysts, which thereby reduces the amount and graphitization degree of carbon deposits. Moreover, the K doping reduces the acid amount of the support and thereby inhibits the formation of carbon deposits as well. However, K doping does not affect the reaction pathway of the catalysts in toluene steam reforming, and the main reaction intermediates detected with in-situ DRIFTS remain the carbonate groups. Furthermore, the confinement effects of the ordered mesoporous structures inhibit the sintering of Ni particles and the formation of carbon deposits. In addition, the influence of different spatial positions of K on the catalysts was explored. It was found that the K introduction via the one-pot solvent evaporation induced self-assembly method can suppress the loss of K from the catalysts.