Effect of Ni/Cu ratio on activity and selectivity of CO2 methanation over Ni‐Cu/SiO2 catalysts

In the present work two series of Ni‐Cu/SiO2 catalysts were evaluated in CO2 methanation. Samples with fixed Ni/Cu ratio and variable total metal loadings, and samples with fixed Ni loadings and variable Ni/Cu ratio were prepared by wet impregnation and characterized by N2 physisorption, X‐ray diffractometry, H2 temperature programmed reduction , scanning electron microscopy with energy dispersive spectroscopy , and temperature programmed oxidation. The catalytic tests were carried out from 250 to 450 °C, H2/CO2 = 4 and 1 atm in a fixed bed tubular reactor with online analysis by gas chromatography. Higher Ni loadings lead to higher Ni° crystallite sizes for samples with fixed Ni/Cu ratio, whereas no difference was observed for samples with variable Ni/Cu ratio. In addition, higher Ni/Cu ratios shifted the reduction temperature to higher values, revealing an increase in metal‐support interaction. Catalysts with Ni/Cu = 10 ratio presented almost equal CO2 conversion regardless of the Ni content, which is attributed to the increase in the Ni° crystallite size as the Ni content increases, whereas the selectivity for CH4 increased with the Ni content due to Ni migration to the surface. For catalysts with fixed Ni content, the higher the Ni/Cu ratio, the greater the CO2 conversion and the CH4 selectivity, demonstrating that the proper adjustment of the Ni/Cu ratio is essential for a high CH4 yield. The catalyst with the highest Ni/Cu ratio achieved a CO2 conversion of 63.3% and CH4 selectivity of 95.7% at 400 °C, showing the greatest resistance to sintering during 5 hr and low carbon formation, which can be attributed to the small crystallite size (∼15 nm) and high metal‐support interaction, resulting from an appropriate Ni/Cu ratio. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.