The reactivity of surface active carbonaceous species with CO2 and its role on hydrocarbon conversion reactions

Carbon deposition on Ni-based catalysts has a significant influence on their cracking activity and selectivity and is the main reason for catalyst deactivation. To understand this behavior, pulse techniques and in situ infrared spectroscopic analysis were applied to the study of the surface carbonaceous species formation and transformation over Ni/MgAl2O4, Ni/MgO/gamma-Al2O3 and Ni/gamma-Al2O3. It was found that MgAl2O4 allows an effective way for CO2 adsorption and activation through the formation of formate/carbonate type species. Carbon adspecies, mainly as CHx (x=1-3), are the intermediates of methane activation on Ni particles and preferably diffuse from the metal to the interference of Ni and the supports and promote the adsorbed CO2 species to decompose and release CO through formate/carbonate type intermediates. The mechanism proposed emphasis the role of these surface species in the surface chemistry of carbonaceous reaction. The data obtained led to a satisfactory description of the working catalyst. (C) 2009 Elsevier B.V. All rights reserved.