A study on the carbonaceous deposition on Ni-Al₂O₃ catalyst in CO₂-CH₄ reforming on the basis of temperature-programmed hydrogenation characterization

Ni-Al₂O₃ catalyst was prepared by hydrothermal deposition method and used in the reaction of CO₂-CH₄ reforming. The effect of reaction time, temperature, CO₂/CH₄ ratio and feed space velocity on the carbonaceous deposition on the Ni-Al₂O₃ catalyst surface in CO₂-CH₄ reforming was investigated, on the basis of temperature-programmed hydrogenation (TPH) characterization. The results indicate that the carbonaceous deposition is an important factor for the deactivation of Ni-Al₂O₃ catalyst in CO₂-CH₄ reforming. The amount of deposited carbon increases with the prolongation of reaction time; meanwhile, the hydrogenation peak in the TPH profiles shifts towards higher temperature, indicating that the graphitization degree of the deposited carbon also increases with prolonging the reaction time. The reaction temperature and feed space velocity, especially the later one, also have an influence on the carbon deposition. In addition, due to the carbon elimination reaction by CO₂ (CO₂+C=2CO), the ratio of CO₂/CH₄ in the feed shows a great influence on the type and amount of carbon deposited on the Ni-Al₂O₃ catalyst. A low CO₂/CH₄ ratio may not achieve a significant inhibition on the coke formation; with the increase of CO₂/CH₄ ratio, the carbon deposition can then be increasingly inhibited; however, a higher CO₂/CH₄ ratio also means higher cost for CO₂ separation and recovery in the product.