Methylcyclohexane dehydrogenation-CO2 methanation coupling reaction over Ni/Mg-Al-O catalysts

Abstract

Integrating the endothermic methylcyclohexane (MCH) dehydrogenation with the exothermic CO2 methanation offers a promising strategy to mitigate catalyst sintering and establish a closed loop for renewable hydrogen storage and CO2 utilization. Here, we developed a series of Ni/Mg-Al-O catalysts from hydrotalcite precursors, with varying Mg/Ni ratios, for this coupled reaction. The catalyst with a Mg/Ni ratio of 5 demonstrated superior performance, achieving 20% MCH conversion and 41% CO2 conversion. Characterization results including XRD, TEM and CO2-TPD revealed that Ni/Mg-Al-O(5) possessed the smallest Ni particle size and the highest concentration of medium-strength basic sites, which facilitate CO2 adsorption and activation, mitigating competitive adsorption with MCH. Furthermore, increasing the Mg content promoted electron transfer between Ni and Mg, strengthening metal-support interactions and leading to the formation of a NiMgO solid solution. This enhanced interaction increased the reduction difficulty of Ni species, which, combined with the trend in Ni particle size, explains the volcanic curve between catalytic performance and Mg/Ni ratio.