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

Abstract

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 °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.

Keywords: CO(2) methanation; Catalyst; Electron transfer; Magnesium hydride; Nickel.