CO₂/H₂ methanation over M*/Mn/Fe-Al₂O₃ (M*: Pd, Rh, and Ru) catalysts in natural gas; optimization by response surface methodology-central composite design

The selective catalytic of carbon dioxide (CO₂) methanation with hydrogen (H₂) over M/Mn/Fe-Al₂O₃ (M = Pd, Rh, & Ru) oxide catalysts in natural gas was investigated. Among them, Ru/Mn/Fe-Al₂O₃ catalyst was found to be the most potential catalyst based on activity. The optimization ratio of Ru, calcination temperature, and catalyst weight loading to improve the efficiency of CO₂ conversion was studied. The results indicated that the Ru/Mn/Fe-Al₂O₃ catalyst ratio (5:35:60), which was calcined at 1,000 °C, was the best catalyst for CO₂ conversion (96.1 %) and CH₄ formation (66.0 %) at reaction temperature at 270 °C. Response surface methodology (RSM) involving central composite design (CCD) was employed to optimize Ru/Mn/Fe-Al₂O₃ and activity parameters (Ru loading, calcination temperature, and catalyst loading) in CO₂ methanation. Under CCD, the model indicated that Ru loading was the most significant effective factor, followed by calcination temperature and catalyst loading. The optimum condition for maximum CO₂ conversion was estimated at 5.5 wt % Ru loading, calcination temperature of 1,010 °C, and catalyst loading of 5 g. Under these conditions, experimental CO₂ conversion efficiency was 95.0 %, which was close with the predicted value of 96.6 %.