The nature and binding strength of carbon adspecies formed during the equilibrium dissociative adsorption of CH4 on Ni-YSZ cermet catalysts

Abstract The equilibrium dissociative adsorption of CH 4 was studied over Ni–YSZ cermet catalysts for a deeper insight regarding the nature and binding strength of generated carbon species on the Ni–YSZ surface. Three main carbon species were detected by the reaction of carbon adspecies with H 2 to produce CH 4 or with O 2 to produce CO and CO 2 . Carbidic species (C c ) are reactive with H 2 and O 2 at temperatures below 600 K while adsorbed carbon (C a ) species in equilibrium with CH x species react with H 2 and O 2 above 600 K. Graphitic carbon layers (C g ) are formed upon CH 4 adsorption above 700 K and its main characteristic is the absence of any reactivity with H 2, to form CH 4 . The binding energy of C a species with respect to graphite decreases with increasing coverage ranging between 7.32±0.03 and 6.5±0.04 eV for the low ( 2 or enhances the reactivity of adsorbed hydrogen atoms toward CH 4 at temperatures higher than 800 K, thus revealing the positive effect of Mo in inhibiting the formation of adsorbed graphitic layers.