Effects of carbon deposition and de-coking treatments on the activation of CH 4 and CO 2 in CO 2 reforming of CH 4 over Ni/yttria-doped ceria catalysts

Abstract

Ni/yttria-doped ceria (YDC) catalysts were employed to study the adsorptive dissociations of CO 2 and CH 4 on Ni and YDC, as well as the effects of carbon deposition and CO 2 de-coking (D–D) treatments of Ni/YDC on the activation of CH 4 and CO 2 in the CO 2–CH 4 reforming reaction. It has been found that both YDC and Ni/YDC are not able to dissociate CO 2 without H 2 pre-reduction. Subjecting YDC to a higher calcination temperature leads to a decrease of the capabilities of YDC to dissociate CO 2 and to release lattice oxygen anions. However, the calcination temperature of YDC has no significant effect on the amount of CO 2 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 CH 4 dissociation is lessened, whereas the de-coking capabilities of CO 2 can be enhanced with each successive D–D treatment.