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.