Effect of high surface area CeO2 and Ce-ZrO2 supports over Ni catalyst on CH4 reforming with H2O in the presence of O2, H2, and CO2

Methane steam reforming over Ni on high surface area (HSA) CeO2 and Ce-ZrO2 supports, synthesized by surfactant-assisted method, was studied and compared to conventional Ni/CeO2, Ni/Ce-ZrO2, and Ni/Al2O3. It was firstly observed that Ni/Ce-ZrO2 (HSA) with the Ce/Zr ratio of 3/1 showed the best performance in terms of activity and stability. This catalyst presented considerably better resistance toward carbon formation than conventional Ni/CeO2, Ni/Ce-ZrO2, and Ni/Al2O3; and the minimum inlet H2O/CH4 ratio requirement to operate without the detectable of carbon are significantly lower. These benefits are related to the high oxygen storage capacity (OSC) of high surface area Ce-ZrO2 support. During the reforming process, in addition to the reactions on Ni surface, the redox reactions between the absorbed CH4 and the lattice oxygen (Ox) on CeO2 and Ce-ZrO2 surface also take place, which effectively prevent the formation of carbon on the surface of Ni.The effects of possible inlet co-reactant, i.e. H2O, H2, CO2, and O2 on the conversion of CH4 were also studied. It was found that H2 presented positive effect on the CH4 conversion when small amount of H2 was introduced; nevertheless, this positive effect became less pronounced and eventually inhibited the conversion of CH4 at high inlet H2 concentration particularly for Ni/CeO2 (HSA) and Ni/Ce-ZrO2 (HSA). The dependence of H2O on the rate was non-monotonic due to the competition of the active sites, as have also been presented by Xu [1], Xu and Froment [2] and [3], Elnashaie et al. [4] and Elnashaie and Elshishini [5]. Addition of CO2 inhibited the reforming rate, whereas addition of O2 promoted the CH4 conversion but reduced both CO and H2 productions.