Cooperative Catalysis of Nickel and Nickel Oxide for Efficient Reduction of CO2 to CH4

The use of CO2 to produce value-added energy chemicals is a promising means for renewable CO2 transformation in low-carbon energy system, and CO2 methanation has attracted ever-increasing interest. Herein, we report that the Ni/MCM-41 catalyst with prominent cooperative effect of Ni and NiO is efficient for CH4 generation with CO2 conversion of 73.2 % and CH4 selectivity of 91.6 % at 400 degrees C and high gas hourly space velocity (GHSV) of 90000 mL g(cat)(-1) h(-1). Combined methodologies of in situ X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, and ambient-pressure X-ray photoelectron spectroscopy reflect the structural evolvements of Ni/MCM-41 catalyst, the presence of carbonyl intermediates, the co-existence of metallic and oxidized Ni species with sufficient molar ratio of Ni-0/Ni2+ under working conditions. H-2 and CO2 molecules are preferentially adsorbed and chemically activated over Ni-0 and Ni2+ species, respectively. The possible four-step reaction mechanism involved carbonyl pathway and the cleavage of C=O bond from CO2 as the rate-determining step over the engineered Ni/MCM-41 catalyst was demonstrated.