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

Direct hydrogenation of CO 2 to synthetic natural gas at a lower temperature remains a big challenge especially in the presence of H 2 S impurity. This contribution describes the synthesis, structure, morphology and doping effect of a series of robust catalysts for CO 2 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 CO 2 conversion (55%) and CH 4 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 CH 4 selectivity of the H 2 S (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% CO 2 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 CO 2 adsorption by lowering the adsorption barrier from 0.55 eV of pure Ni to 0.12 eV, and further inhibit the gaseous H 2 S from chemisorbing on the catalyst surface owning to the relatively unstable Ni-S bond.