MnO _<i>x</i> -Promoted Ni/ZrO ₂ Catalyst with High Nickel Loading for Enhanced Low-Temperature CO ₂ Methanation

Developing high-performance, non-precious-metal catalysts that operate efficiently at low temperatures remains a pivotal challenge for CO2 methanation, particularly for systems with high active metal loadings where nanoparticle sintering often compromises performance. Herein, Mn-promoted Ni/ZrO2 catalysts with 40 wt % Ni were prepared via a Pechini method, demonstrating exceptional low-temperature performance. Under atmospheric pressure, the optimized 5Mn–Ni/ZrO2 catalyst achieved stable 70% CO2 conversion, near-100% CH4 selectivity, and a stable CH4 yield of 150 mmol/g/h for 117 h at 225 °C. Comprehensive characterization (XRD, TEM, XPS, H2-TPR, CO2-TPD, H2-TPD) revealed that Mn doping facilitates NiO reduction with higher Ni dispersion, increases electron density on Ni sites, and increases the population of medium-strength basic sites and oxygen vacancies on the ZrO2 support. These synergistic modifications collectively promote CO2 adsorption, H2 adsorption, and catalyst reducibility. In situ DRIFTS further identified a formate-mediated pathway, in which Mn promotes the stabilization and subsequent hydrogenation of the HCOO* intermediate. This work demonstrates that rational exploitation of promoter-support synergy can overcome the dispersion limitations inherent to high-loading Ni catalysts, providing an effective design strategy for advanced, low-temperature CO2 methanation catalysts.