CO2 Methanation over Mn-Promoted Co-Precipitated Ni-Based Catalysts with Enhanced Catalytic Activity

The methanation of CO₂ is a sustainable pathway for converting CO₂ into useful fuel products and chemicals. Due to the poor activity of Ni monometallic catalyst, the development of efficient low-temperature catalysts is an indispensable matter of research. Herein, Mn-promoted Ni/MgO catalysts were synthesized by co-precipitation method and applied for CO₂ methanation, in order to investigate the effect of Mn doping on the catalytic performance of the resultant catalysts. Various characterization methods, including XRD, H₂-TPR, BET, SEM, ICP-AES, and TEM, were employed to analyze the morphology and structure of the catalysts. The results of XRD and TEM confirmed that the introduction of Mn was helpful to promote the dispersion of Ni species and reduce the crystallite size of active Ni components. H₂-TPR results indicated that an appropriate amount of Mn doping could weaken the interaction between Ni species and the support, thus facilitating the reduction of Ni species. Besides, BET analysis showed that the addition of Mn improved the pore structure of the catalyst, such as the specific surface area and pore volume. These characterizations suggested that the synergetic effects between Ni and Mn species, including good Ni dispersion, improved number of CO₂ adsorption sites and suitable pore structure, were considered as significant factors for enhanced catalytic performance of the Mn-promoted catalysts. Accordingly, Ni–0.01Mn/MgO with Mn/Mg molar ratio of 0.01 exhibited the highest catalytic activity as compared to Ni/MgO, with CO₂ conversion of 73.2% and CH₄ selectivity of 99.4% at 300°C, and CO₂ conversion of 81.8% and CH₄ selectivity of 99.2% at 350°C, respectively. After 60 h of stability test at 300°C, Ni–0.01Mn/MgO still maintained the catalytic activity. This would offer an important opportunity to achieve an efficient co-precipitated CO₂ methanation catalyst, which could be a good way to reduce CO₂ emissions.