Ni/M/SiO2 catalyst (M=La, Ce or Mg) for CO2 methanation: Importance of the Ni active sites

The hydrogenation of CO2 to methane with renewable H2 can mitigate the greenhouse effect and realize the sustainable energy production. The SiO2 supported Ni catalysts were prepared via a simple combustion-impregnation method. Highly dispersed Ni particles were obtained, accompanied by increased H2 and CO2 adsorption capacity. And the Ni active sites and the catalyst adsorption capacity to H2 and CO2 were modified by different promoters (La, Ce, or Mg). La and Ce were conducive to Ni dispersion and catalyst reducibility, bringing in more active sites and further enhanced catalytic activity at low temperatures. Conversely, the slight agglomeration of Ni particles and reduced catalyst reducibility were found on the catalyst with Mg, resulting from the formation of solid solution. Moreover, Mg atoms were prone to enrich on the surface of catalyst, which may cover part of Ni active sites and make them inaccessible. Therefore, though the largest H2 and CO2 adsorption capacity were achieved on the catalyst with Mg, it displayed the poor catalytic performance. Hence, the importance of the Ni active sites on the low-temperature activity of catalyst in CO2 methanation was confirmed in this work. Besides, the increased CO2 activation ability benefiting from the promoter could facilitate the catalytic activity at low temperatures. The fundamental findings in this work may help develop an efficient Ni-based catalyst for CO2 methanation at low temperatures.