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The utilization of fossil fuels has led to a gradual increase in greenhouse gas emissions, which have accelerated global climate change. Therefore, there is a growing interest in renewable energy sources and technologies. Biogas has gained considerable attention as an abundant renewable energy resource. Common biogases include anaerobic digestion gas and landfill gas, which can be used to synthesize high-value-added syngas through catalytic reforming. Because syngas (CO and H₂) is synthesized at high reaction temperature, carbon is generated by the Boudouard reaction from CO and CH₄ cracking; thus, C blocks the pores and surface of the catalyst, thereby causing catalyst deactivation. In this study, a simulation was performed to measure the CH₄ and CO₂ conversion rates and the syngas yield for different ratios of CO₂/CH₄ (0.5, 1, and 2). The simulation results showed that the optimum CO₂/CH₄ ratio is 0.5; therefore, biogas reforming over the 3 wt% Ni/Ce-MgO-ZrO₂/Al₂O₃ catalyst was performed under these conditions. CH₄ and CO₂ conversion rates and the syngas yield were evaluated by varying the <i>R</i> values (<i>R</i> = (CO₂ + O₂)/CH₄) on the effect of CO₂ and O₂ oxidants of CH₄. In addition, steam was added during biogas reforming to elucidate the effect of steam addition on CO₂ and CH₄ conversion rates. The durability and activity of the catalyst after 200-h biogas reforming were evaluated under the optimal conditions of <i>R</i> = 0.7, 850 &#176;C, and 1 atm.