The role of ceria in promoting Ni catalysts supported on phosphate-modified zirconia for the partial oxidation of methane

Abstract

The catalytic partial oxidation of methane (POM) is aimed at the mitigation of CH₄ (a highly potent greenhouse gas) from the environment and the synthesis of syngas with a high H₂/CO ratio. Herein, to enhance the POM reaction, Ni-supported phosphate-modified-zirconia were synthesized with promotor “Ce” to achieve high H₂/CO ratio (2.4–3.2). The catalysts were characterized by surface area and porosity, X-ray diffraction, RAMAN, temperature-programmed experiments (TPR, CO₂-TPD, and TPO), and TEM. Increasing the ceria addition over 10Ni/PO₄ + ZrO₂ resulted in lower crystallinity, higher dispersion of active sites, and enhanced the surface area of catalyst. The unique and prominent reducibility and basicity of NiO-species and surface oxide ions, respectively, are particularly notable at 4 wt.% ceria loading. At a reaction temperature of 600°C, the highest concentration of active sites and a unique concentration of moderate strength basic sites can be achieved with 4 wt.% ceria loading over 10Ni/PO₄ + ZrO₂. This leads to 44% conversion of CH₄, 36% yield of H₂, 35% yield of CO₂, and H₂/CO ratio of 3.16 for the POM reaction. The cyclic H₂TPR-O₂TPO-H₂TPR experiment confirms the reorganization of the active site towards high temperature under oxidizing gas O₂ and reducing gas H₂ gas stream during the POM reaction.