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

Abstract

This research developed hierarchical 10 wt % Ni-1 wt % ZrO 2 /Al 2 O 3 catalysts for combined steam and CO 2 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 H 2 selectivity, reaching an appropriate H 2 /CO ratio (1.9–2.0) in FT subunits in the GTL process when nanosheets existed on the surface due to the increase in H 2 O adsorption-dissociation sites. The good dispersion of hierarchical nanosheets accompanied by the ZrO 2 promoter successfully enhanced the CH 4 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 H 2 O activation-dissociation sites that allowed CO 2 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.

Enhancement of Ni-NiO-CeO2 Interaction on Ni–CeO2/Al2O3-MgO Catalyst by Ammonia Vapor Diffusion Impregnation for CO2 Reforming of CH4

“…Moreover, the highest H 2 yield (62.3%), the highest CO yield (95.3%) and the slightly higher H 2 /CO ratio (0.59) observed on the 5Ni5Ce(20 h)/MA catalyst imply a reduced RWGS side reaction effect. This is assigned to the rehydration property promoting H 2 O adsorption-dissociation [20].…”

“…This network of metal oxide nanoparticles is clearly visible on 5Ni5Ce(20 h)/MA (Figure 1c), implying the growth of the NiO-CeO 2 interaction throughout the ammonia vapor diffusion. This can be explained by layered double hydroxide (LDH) synthesis via ammonia vapor diffusion impregnation [19][20][21]. When ammonia vapor is dissolved into the impregnated nickel-cerium nitrate solution on the support, a limited amount of hydroxide ions are produced, conducting the slow growth of the layered double hydroxide ([Ni 1−-x Ce x (OH) 2 ] z+ (NO 3 ) z •nH 2 O) throughout the diffusion time [22][23][24].…”

“…A 10 wt% Ni-1 wt% ZrO 2 /Al 2 O 3 catalyst prepared by a similar method with an ammonia diffusion time of 6 h demonstrated an improvement in the steam activationdissociation and coke resistance for the combined steam and CO 2 reforming of methane (CSCRM) process operated under low-temperature and low-steam conditions. This can be attributed to the very dispersive nanosheets and redox properties of the ZrO 2 promoter that produces the number of the OH* and O* species on the surface [20]. Consequently, it would be interesting to develop the heterogeneity of Ni-CeO 2 networks on catalyst surface through time-controlled ammonia diffusion treatment to investigate its effect on properties, CRM performance, and deactivation.…”