Effect of NH3 Alkalization and MgO Promotion on the Performance of Ni/SBA-15 Catalyst in Combined Steam and Carbon Dioxide Reforming of Methane.

In this work, 31.4 wt.% Ni/SBA-15 (Ni/SBA-15) nonpromoted and alkalized with ammonia solution and by MgO promoter catalysts were prepared and used for combined steam and CO₂ reforming of CH₄ (bireforming). Effect of concentration of ammonia solution (NH_3(aq)) (10–25 vol.%) and Mg content (3–12 wt.%) on the properties of the Ni/SBA-15 catalysts was investigated by low-angle and powder X-ray diffraction (XRD), N₂-BET isothermal adsorption, SEM, TEM, EDS mapping, H₂-TPR, and CO₂-TPD methods. The performance of the catalysts in bireforming was assessed in the temperature range of 550–800°C. The enhancement of dispersion of NiO particles, reducibility, and basicity of alkalized Ni/SBA-15 catalysts were responsible for improving the catalytic performance of this catalyst. The results revealed that the Ni/SBA-15 treated with 15-25% NH_3(aq) solution and promoted with 3-9% Mg exhibited high activity for CH₄ conversion. Meanwhile, Ni6Mg/SBA-15 showed the highest CO₂ conversion. Among tested catalysts, Ni/SBA-15-20NH₃ and Ni9Mg/SBA-15 samples had an almost equal activity with a CH₄ conversion of nearly 97% and a CO₂ conversion of about 84% at 700°C thanks to its moderate affinity with both CO₂ and CH₄. However, the H₂/CO ratio of the product mixture remained at 2.02 on the Ni/SBA-15-20NH₃ catalyst and almost 1 on the Ni9Mg/SBA-15 sample. These results might be related to the fact that the alkalization of the Ni/SBA-15 catalyst by NH_3(aq) solution had an advantage over using MgO because side reactions were unlikely to occur. [ABSTRACT FROM AUTHOR]