The study of CO₂ reforming of methane over Ce/Sm-promoted NiCaAl catalysts

In this work, we synthesized Ce and Sm-promoted NiCaAl layered catalysts via co-precipitation and freeze-drying strategies for alleviating some problems, such as coke deposition and agglomeration of active sites, in dry reforming of methane. Employing such promoters leads to rising O₂ vacancies on the catalyst's surface, resulting from adsorbing CO₂ gas under the reaction. X-ray diffraction (XRD) analysis confirmed the formation of a hydrotalcite network. High-resolution transmission electron microscopy (HR-TEM) and field emission scanning electron microscopy (FE-SEM) images also indicated a wealth of nanocatalysts, well distributed on the surface and within a porous scaffold structure. The temperature-programmed reduction (H₂-TPR) proved that cerium (H₂ consumption = 1.2 mmol.g^-1) could weaken the interactions between nickel and Ca/Al, leading to better reducibility than samarium (H₂ consumption = 1.35 mmol.g^-1). Moreover, the temperature-programmed deposition (CO₂-TPD) showed the Ce-promoted catalyst possesses more basic sites (0.41 mmol.g^-1) on its surface than the Sm-enhanced one (0.25 mmol.g^-1). Consequently, the Ce-enhanced catalyst with a smaller crystallite size (8.9 nm), higher dispersion of Ni (10.8%), better reducibility, and more basic sites, which caused the highest methane conversion (82%), and H₂/CO ratio (0.9) at 700 °C without any coke deposition after 5 h of time on stream.