Efficient sulfur resistance of Fe, La and Ce doped hierarchically structured catalysts for low-temperature methanation integrated with electric internal heating

Abstract

Direct hydrogenation of CO2 to synthetic natural gas at a lower temperature remains a big challenge especially in the presence of H2S impurity. This contribution describes the synthesis, structure, morphology and doping effect of a series of robust catalysts for CO2 methanation under resistive heating, based on Ni-layered double hydroxides (LDH) grown on porous and electrically conductive nickel foam (NF) derived structured catalysts. As a result, LaNi/NF showed the highest CO2 conversion (55%) and CH4 formation rate (631.5 mmol·g−1·h−1) at lower temperature of 250 °C and FeNi/NF gave the optimal conversion at 350 °C (75%, 860.9 mmol·g−1·h−1), which was superior to the most of recently reported Ni-based supported catalysts. We found that the CH4 selectivity of the H2S (50 ppm) poisoned catalysts was significantly decreased and CO was verified as the main by-product. In this case, LaNi/NF and FeNi/NF still retained much higher conversion rate at 300 °C, 29.8% for LaNi/NF and 27% for FeNi/NF, than the almost deactivated unmodified Ni/NF with maximum 5% CO2 conversion. The extraordinary activities can be explained as that the dopants can greatly strengthen the metal-support interaction and further enhance the reducibility of active metallic Ni, as XRD, HRTEM, TPR and XPS indicated. Besides of this, DFT calculations demonstrated that the existence of La can greatly promote CO2 adsorption by lowering the adsorption barrier from 0.55 eV of pure Ni to 0.12 eV, and further inhibit the gaseous H2S from chemisorbing on the catalyst surface owning to the relatively unstable Ni-S bond.