Influence of the nanoscale support on carbon deposition and carbon elimination over Ni/gamma-Al2O3 catalyst for CH4 conversion.

Characteristics of carbon deposition by CH4 and carbon elimination by CO2 over conventional and nanoscale Ni/gamma-Al2O3 catalysts were investigated by using a pulse reaction, as well as by TGA, TEM, TPO-MS, H2-TPR and H2-chemisorption techniques. It was found that the behaviors of carbon deposition by CH4 decomposition and carbon elimination by CO2 depend on the active metal dispersion and the metal-support interaction. The filamentous carbon was formed on the conventional Ni/gamma-Al2O3 catalyst with low metal dispersion and relatively large particles, this type of filamentous carbon was far from the active centers and difficult to eliminate by CO2. On the other hand, the carbon deposition originated from CH4 decomposition on the nanoscale Ni/gamma-Al2O3 catalyst would mainly cover the surface of active centers, this type of highly active carbon was easily eliminated by CO2 because it is close to the active center Ni atoms. As a result, the improvement of coking-resistance was ascribed to the high metal dispersion and strong metal-support interaction, a model of CH4 decomposition carbon deposition on Ni/gamma-Al2O3 catalyst was proposed.