A novel ammonia vapour diffusion‐assisted impregnation technique was developed to synthesize the Al2O3‐MgO‐supported hierarchical Ni nanosheets. The resulting catalysts with different times for ammonia vapour treatments (at 12 hours, 18 hours, and 20 hours) were prepared to investigate the growth of Ni nanosheets on the catalyst surface. All catalysts were tested for CO2 reforming of methane and a comprehensive characterization study was conducted by XRD, N2 adsorption‐desorption, H2‐TPD, H2‐TPR, CO2‐TPD, and TGA. The Ni nanosheets were obtained using the ammonia vapour treatment for 20 hours, improving the selectivity toward H2 generation without a lower CH4 conversion. When compared to the reference catalyst prepared by a conventional impregnation method, the H2/CO ratio for CO2 reforming of the methane process was enhanced by 0.35. Additionally, the carbon deposition was reduced by half using hierarchical Ni nanosheets for the CO2 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 CO2 activation‐dissociation pathways, preventing carbon formation and inhibiting the reverse water gas shift.