Bimetallic Ni-Fe catalysts for methanation of CO2: Effect of the support nature and reducibility

A series of Ni-Fe bimetallic catalysts supported on high surface area of Ce0.8Zr0.2O2 (CZ) and SiO2 (S) were prepared by impregnation (10 wt% of metal charge) with different Ni:Fe ratios (10:0, 9:1, 3:1 and 1:1) and the effect of Fe content on promotion of CO2 methanation was investigated. Hydrogen reduction favors Fe incorporation into the Ni structure, forming Ni1-xFex alloys, whereas some Fe-O species remain unreduced. Ni-Fe/CZ catalysts showed a promoted reducibility at low temperature as well as high density of weak and medium basic sites in comparison with Fe-Ni/S catalysts. Activity tests revealed that CO2 conversion and CH4 selectivity increases with the decrease of Fe content. In the bimetallic catalysts, the presence of unreduced Fe-O species restricts the contact between hydrogen supplied by Ni1-xFex and adsorbed CO2. Superior activity of Ni/CZ was associated to the close location of medium basic sites and Ni nanoparticles to activate hydrogen. Microstructural studies of Ni/CZ catalyst after prolonged operation demonstrated the absence of carbon deposition and good Ni availability on the CZ surface.