Why Ni/CeO2 is more active than Ni/SiO2 for CO2 methanation? Identifying effect of Ni particle size and oxygen vacancy

An impregnated Ni/CeO2 catalyst with an array structure and a phyllosilicate-based Ni/SiO2 catalyst prepared by hydrothermal method were designed for CO2 methanation. The as-synthetized Ni/SiO2 catalyst exhibits a high Ni content of 25.9 wt%, while its CO2 conversion at low temperature is far lower than that of Ni/CeO2, whose Ni content is only 10.0 wt%. TEM and XRD results show that the Ni/CeO2 catalyst possesses very tiny Ni particle size of around 1.2 nm, which leads to large H2 uptake capacity. XPS and Raman analyses indicate that Ni/CeO2 obtains more oxygen vacancies resulting in promotion of the CO2 activation. The combined effect of the Ni/CeO2 catalyst to enhance chemisorption of H2 and CO2 leads to high low-temperature activity.