MgH2-modified Ni catalysts with electron transfer behavior for improving CO2 methanation

The activation of CO2 plays a crucial role in the process of CO2 methanation. It is important to raise the electron density of the active site to facilitate electron transfer to CO2. However, the modulation of Ni catalytic activity by direct mixing of metal hydrides has received limited attention. In this study, MgH2-xNi catalysts with varying molar ratios were prepared using a simple mechanical ball-milling method for the CO2 methanation reaction. The H- of MgH2 with high electron density can transfer electrons to the active center Ni. The experimental results indicated that the addition of MgH2 notably improved the catalytic activity of Ni. At 350 degrees C, the CO2 conversion and CH4 selectivity of MgH2-5Ni were 91.78 % and 99.48 %, which were improved by 62.26 % and 18.10 %, respectively, compared with those of Ni. Various characterizations showed that MgH2 can raise the electron density of Ni, and the MgH2-xNi catalysts exhibited a high content of surface-adsorbed oxygen, along with a significant number of weak and medium-strength basic sites. Furthermore, density functional theory (DFT) calculations validated that the increased electron density of Ni facilitated the adsorption and activation of CO2, while significantly reducing the energy barrier for COOH* formation. This study provides a simple and effective method to raise the electron density of Ni, which is important for the development of catalysts for CO2 methanation.