Enhancing activity for carbon dioxide methanation by encapsulating (1 1 1) facet Ni particle in metal–organic frameworks at low temperature

Abstract

In this work, we developed Ni nanoparticles (NPs) encapsulated in a highly ordered MIL-101 as catalysts for CO2 methanation by double solvent method (DSM) and multiple impregnation method (IM). The 20Ni@MIL-101(DSM) catalyst exhibited unexpectedly higher activity (CH4 TOF was 1.63×10−3s−1 at 300°C), thermal stability and lower activation energy (88.01kJ/mol) for CO2 methanation than the 20Ni@MIL-101(IM) catalyst. Based on activity results and characterization studies using XRD, H2-TPR, BET, TEM, XPS, FT-IR and TGA techniques, the small-sized high dispersion Ni NPs in the frameworks of 20Ni@MIL-101(DSM) exposed Ni(111) facet are main active species. The results of density-functional theory (DFT) calculations indicated that the potential energy barrier was about 10.0kcal/mol for CO2 dissociation into COads and Oads over the Ni(111) surface, which was lower than Ni(200) plane (20.3kcal/mol). These results uncover the dependence of the activation energy of the CO2 methanation on the Ni plane over Ni-based catalysts. These understandings will probably be applicable in the development of highly efficient CO2 methanation catalysts at low temperature region.