A novel ammonia vapour diffusion-assisted impregnation technique was developed to synthesize the Al 2 O 3 -MgO-supported hierarchical Ni nanosheets. The resulting catalysts with different times for ammonia vapour treatments (at 12, 18, and 20 hours) were prepared to investigate the growth of Ni nanosheets on the catalyst surface. All catalysts were tested for CO 2 reforming of methane and a comprehensive characterization study was conducted by XRD, N 2 adsorption-desorption, H 2 -TPD, H 2 -TPR, CO 2 -TPD, and TGA. The Ni nanosheets were obtained using the ammonia vapour treatment for 20 hours, improving the selectivity toward H 2 generation without a lower CH 4 conversion. When compared to the reference catalyst prepared by a conventional impregnation method, the H 2 /CO ratio for CO 2 reforming of the methane process was enhanced by 0.35. Additionally, the carbon deposition was reduced by half using hierarchical Ni nanosheets for the CO 2 reforming of methane at 620 C for 20 hours. The mechanism of this improvement was achieved by the increase in medium basicity associated with a strong metal-support interaction that promotes the CO 2 activation-dissociation pathways, preventing carbon formation and inhibiting the reverse water gas shift.

In this paper, the 10 wt% Ni/Al2O3-MgO (10Ni/MA), 5 wt% Ni-5 wt% Ce/Al2O3-MgO (5Ni5Ce/MA), and 5 wt% Ni-5 wt% Co/Al2O3-MgO (5Ni5Co/MA) catalysts were prepared by an impregnation method. The effects of CeO2 and Co doping on the physicochemical properties of the Ni/Al2O3-MgO catalyst were comprehensively studied by N2 adsorption-desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), H2 temperature programmed reduction (H2-TPR), CO2 temperature programmed reduction (CO2-TPD), and thermogravimetric analysis (TGA). The effects on catalytic performance for the combined steam and CO2 reforming of methane with the low steam-to-carbon ratio (S/C ratio) were evaluated at 620 °C under atmospheric pressure. The appearance of CeO2 and Co enhanced the oxygen species at the surface that decreased the coke deposits from 17% for the Ni/MA catalyst to 11–12% for the 5Ni5Ce/MA and 5Ni5Co/MA catalysts. The oxygen vacancies in the 5Ni5Ce/MA catalyst promoted water activation and dissociation, producing surface oxygen with a relatively high H2/CO ratio (1.6). With the relatively low H2/CO ratio (1.3), the oxygen species at the surface was enhanced by CO2 activation-dissociation via the redox potential in the 5Ni5Co/MA catalyst. The improvement of H2O and CO2 dissociative adsorption allowed the 5Ni5Ce/MA and 5Ni5Co/MA catalysts to resist the carbon formation, requiring only a low amount of steam to be added.

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Abstract10 wt% (Ni-Co) catalysts with different Ni and Co content : 10%Ni, 9%Ni1%Co, 7%Ni3%Co, 5%Ni5%Co, 3%Ni7%Co, and 10%Co; .