A novel process of triple-passed CO₂ methanation over gradient-coated spiral-structured Ni/CeO₂ catalysts

The objective of this study is to develop an efficient gradient spiral-structured Ni/CeO₂ catalyst for CO₂ methanation. The spiral-structured Ni/CeO₂ catalysts were prepared by the gradient coating method. The process employs a triple-passed operation for steam trapping to increase the CH₄ product at flow rates from 100 to 3000 ml/min. At a low flow rate (100 ml/min), a triple-passed reactor's CO₂ conversion efficiency (98.5%) and CH₄ selectivity (99.9%) are slightly greater than those of a single-passed reactor (96.4% and 99.9%, respectively). When operating at a high flow rate of 3000 ml/min, a triple-passed reactor can reach up to 83.4% CO₂ conversion efficiency and 94.9% CH₄ selectivity, whilst a single-passed reactor can only achieve 64% CO₂ conversion and 87.4% CH₄ selectivity. In addition, the spiral structure can enhance heat transfer, eliminating hotspots as well as improving mass transfer by swirling flow. The development of gradient coating could be beneficial for conducting thermal energy from a thick-coated front spiral-catalyst to a thinner-coated terminal spiral-catalyst. Furthermore, the steam trapping would further increase CO₂ conversion as well as CH₄ selectivity.