| Summary: | Biogas is mainly composed of CH<sub>4</sub> and CO<sub>2</sub>, so it is used as an alternative energy to CH<sub>4</sub> with high energy density by separating and removing CO<sub>2</sub> from biogas. In addition, it can be utilized by producing synthesis gas (CO and H<sub>2</sub>) through thermal decomposition of biogas or by synthesizing CH<sub>4</sub> by methanation of CO<sub>2</sub>. The technique of CO<sub>2</sub> methanation is a method that can improve the CH<sub>4</sub> concentration without CO<sub>2</sub> separation. This study aims to produce more efficient methane through CO<sub>2</sub> methanation of biogas over Ni-Mg-Al catalyst. So, the effect of Ni contents in catalyst, catalyst reduction temperature, CO<sub>2</sub> concentration in biogas, and the initial concentration of CH<sub>4</sub> on CO<sub>2</sub> conversion rate and CH<sub>4</sub> selectivity was investigated. In addition, the effect of increasing CO<sub>2</sub> concentration, H<sub>2</sub>/CO<sub>2</sub> ratio, and GHSV (gas space velocity per hour) on H<sub>2</sub> conversion, CH<sub>4</sub> productivity, and product was investigated. In particular, the durability and stability of CO<sub>2</sub> methanation was tested over 60 wt% Ni-Mg-Al catalyst at 350 °C and 30,000/h for 130 h. From the long-term test results, the catalyst shows stability by maintaining a constant CO<sub>2</sub> conversion rate of 72% and a CH<sub>4</sub> selectivity of 95%.
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