Pt-induced, efficient methylcyclohexane de-hydrogenation-CO2 hydrogenation coupling reaction over NixPt/Mg-Al-O for CO2 methanation

Abstract

The high cost and potential hazards associated with hydrogen storage and transportation pose notable barriers to the industrial application of the CO₂ methanation. Herein, a new reaction pathway is proposed using the liquid organic hydrogen carrier Methylcyclohexane (MCH) as a hydrogen source to couple the endothermic MCH de-hydrogenation reaction with the exothermic CO₂ methanation reaction, which is achieved using NiPt-modified layered double hydroxide-derived catalysts Ni_xPt/Mg-Al-O. The activity results indicate that the coupling reaction overcomes the thermodynamic limitations of traditional CO₂ methanation by coupling the endothermic and exothermic processes. CO₂ conversion reaches 91 % at 450 °C. The addition of Pt induces the formation of the Ni^δ+-Pt^δ− structure and creates more defect sites, which are considered critical factors influencing the activity and mechanism of the coupled reaction. The electron transfer within the NiPt alloy enhances the de-hydrogenation rate of MCH and improves the adsorption capacity for CO* intermediate species. In addition, more defect sites facilitate the adsorption of CO₂ onto the support and prevent its competitive adsorption with that of MCH onto metal sites. Furthermore, the hydrogen spillover effect on Ni_xPt/Mg-Al-O catalysts enables H* species to rapidly react with CO₂ adsorbed onto the support to produce CH₄. In situ diffuse reflectance infrared Fourier transform spectroscopy studies reveal that the coexistence of the CO* and HCOO* routes on Ni₆₀Pt/Mg-Al-O catalysts may potentially facilitate the induced efficient catalytic conversion in the coupled reaction.