LaCe co-doped Ni/MgO-Al2O3 catalyst: deactivation mechanism study for CO2 methanation

Ni-based catalysts suffer from deactivation due to high-temperature sintering and oxidation during CO 2 methanation, limiting their industrial application. Single La or Ce promotion can improve Ni dispersion and suppress sintering; however, La and Ce co-doping unexpectedly aggravates catalyst deactivation. In this study, a new deactivation mechanism of LaCe co-doped Ni/MgO-Al 2 O 3 catalysts during CO 2 methanation at 500 °C and 3 MPa is revealed. Combined characterization by XRD, H 2 -TPR, CO 2 -TPD, XPS and TEM, together with DFT calculations, suggests that the formation of a La 2 O 3 -CeO 2 solid solution inhibits MgO dispersion in the support, resulting in a higher amount of free Al 2 O 3 . Meanwhile, Ce promotes the oxidation of surface Ni, and the resulting Ni δ+ species are more prone to react with Al 2 O 3 to form hardly reducible NiAl 2 O 4 spinel, causing irreversible deactivation. Further adoption of a La-first impregnation strategy improves MgO dispersion, suppresses NiAl 2 O 4 formation, retains more oxygen vacancies, and enhances Ni dispersion, thereby mitigating deactivation. This study reveals a new deactivation mechanism induced by LaCe co-doping, providing a theoretical basis for rational design of high-stability Ni-based CO 2 methanation catalysts.