Effect of Ni/Cu ratio on activity and selectivity of CO<sub>2</sub> methanation over Ni‐Cu/SiO<sub>2</sub> catalysts
Yan Resing Dias, Oscar W. Perez‐Lopez
Abstract
Abstract In the present work two series of Ni‐Cu/SiO 2 catalysts were evaluated in CO 2 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 N 2 physisorption, X‐ray diffractometry, H 2 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, H 2 /CO 2 = 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 CO 2 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 CH 4 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 CO 2 conversion and the CH 4 selectivity, demonstrating that the proper adjustment of the Ni/Cu ratio is essential for a high CH 4 yield. The catalyst with the highest Ni/Cu ratio achieved a CO 2 conversion of 63.3% and CH 4 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.