Combined Steam and CO₂ Reforming of Methane over the Hierarchical Ni-ZrO₂ Nanosheets/Al₂O₃ Catalysts at Ultralow Temperature and under Low Steam

This research developed hierarchical 10 wt % Ni-1 wt % ZrO₂/Al₂O₃ catalysts for combined steam and CO₂ reforming of methane (CSCRM) reaction to produce syngas for gas-to-liquid (GTL) application under the ultralow temperature and low steam condition. The hierarchical nanosheet catalysts were prepared via a novel impregnation technique assisted by ammonia vapor diffusion with various times (1, 6, and 12 h) to develop the different magnitude of hierarchical nanosheets on the surface. Then, CSCRM at 600 °C was performed on the catalysts for 6 h. The results evidenced the improvement of H₂ selectivity, reaching an appropriate H₂/CO ratio (1.9-2.0) in FT subunits in the GTL process when nanosheets existed on the surface due to the increase in H₂O adsorption-dissociation sites. The good dispersion of hierarchical nanosheets accompanied by the ZrO₂ promoter successfully enhanced the CH₄ conversion and the coke prevention through the spread nanosheets because of the increase in the number of active sites and the surface interaction. The interaction of hierarchical nanosheets created the H₂O activation-dissociation sites that allowed CO₂ to be selective on the oxygen vacancy sites, producing more OH* and OH* on the catalyst surface to resist the carbon deposition during CSCRM operation.