CO2 methanation over Ni/SiO2-Al2O3 catalysts: effect of Ba, La, and Ce addition

One of the most technologically and financially feasible methods for managing anthropogenic CO2 emissions is CO2 hydrogenation to methane. However, the high efficiency of mostly used nickel-based catalysts is still a challenge in the CO2 methanation process. Herein, 10% silica-90% alumina, commercially known as SIRAL-10, was used as a support for nanostructured Ni catalysts. Modified SIRAL-supported nickel catalysts (Ni/SA) with Ba, La, and Ce metals as promoters were prepared by a simple wet impregnation method. These catalysts were tested for atmospheric CO2 methanation reaction in a 250-500 degrees C temperature range in a tubular fixed bed reactor with a H-2/CO2 molar ratio of 4. As prepared samples were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, hydrogen temperature-programmed reduction (H-2-TPR), carbon dioxide temperature-programmed desorption (CO2-TPD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). CO2 methanation was found to be highly dependent on surface basic sites and Ni dispersion. Ni active sites were mainly obtained from the reduction of strongly interacted NiO at temperatures >700 degrees C. All promoted catalysts showed better catalytic activity than unpromoted nickel catalysts. Maximum CO2 conversion of 85.6% was obtained on the Ba-promoted sample at 400 degrees C, while low-temperature catalyst activity was achieved in the case of Ce-Ni/SA. The catalysts exhibited CH4 selectivity in the following order: Ce-Ni/SA > Ba-Ni/SA > La-Ni/SA > Ni/SA. The Ce-containing sample showed exceptional catalytic performance with about 78.4% CO2 conversion and 98% CH4 selectivity at 350 degrees C. Both Ba and Ce-promoted catalysts exposed the best stability for 24 hours. Unique features of the SIRAL support and the addition of basic promoters facilitated the sequential hydrogenation of CO2 to produce almost CO-free CH4.