Effects of carbon deposition and de-coking treatments on the activation of CH4 and CO2 in CO2 reforming of CH4 over Ni/yttria-doped ceria catalysts

Ni/yttria-doped ceria (YDC) catalysts were employed to study the adsorptive dissociations Of CO2 and CH4 on Ni and YDC, as well as the effects of carbon deposition and CO2 de-coking (D-D) treatments of Ni/YDC on the activation of CH4 and CO2 in the CO2-CH4 reforming reaction. It has been found that both YDC and Ni/YDC are not able to dissociate CO2 without H-2 pre-reduction. Subjecting YDC to a higher calcination temperature leads to a decrease of the capabilities of YDC to dissociate CO2 and to release lattice oxygen anions. However, the calcination temperature of YDC has no significant effect on the amount of CO2 dissociated by Ni/YDC catalysts. Because of the morphological changes of filamentous carbon whiskers on the surface of Ni/YDC catalysts, surface areas of the active nickel species are increased progressively in the first three D-D treatments, thereby concurrently enhancing the effect of interfacial metal oxide-support interaction in the reforming reaction. Consequently, the extent of carbon deposition through CH4 dissociation is lessened, whereas the de-coking capabilities Of CO2 can be enhanced with each successive D-D treatment. (C) 2004 Elsevier B.V. All rights reserved.