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

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 H-2/CO ratio. Herein, to enhance the POM reaction, Ni-supported phosphate-modified-zirconia were synthesized with promotor "Ce" to achieve high H-2/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 degrees 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 H-2, 35% yield of CO2, and H-2/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 O-2 and reducing gas H-2 gas stream during the POM reaction.