Synthesis gas production from dry reforming of methane over CeO2 doped Ni/Al2O3: Influence of the doping ceria on the resistance toward carbon formation

Abstract

Abstract Doping of CeO2 as an additive promoter on Ni/Al2O3 was found to improve dry reforming activity for H2 and CO productions at solid oxide fuel cell (SOFC) operating temperature (800–900 °C). The catalyst provides significantly higher reforming reactivity and resistance toward carbon deposition compared to conventional Ni/Al2O3. These enhancements are mainly due to the influence of the redox property of ceria. During dry reforming process, in addition to the reactions on Ni surface, the gas–solid reactions between the gaseous components presented in the system (CH4, CO2, CO, H2O, and H2) and the lattice oxygen (Ox) on ceria surface also take place. The reactions of adsorbed methane and carbon monoxide (produced during dry reforming process) with the lattice oxygen (Ox) on ceria surface (CH4 + Ox → CO + H2 + Ox−1 and CO + Ox ⇔ CO2 + Ox−1) can prevent the formation of carbon species on Ni surface from methane decomposition reaction and Boudard reaction. In particular, CeO2 doped Ni/Al2O3 with 8% ceria content showed the best reforming activity among those with the ceria content between 0 and 14%. The amount of carbon formation decreased with increasing Ce content. However, Ni was oxidized when more than 10% of ceria was doped. According to the post-XPS measurement, a small formation of Ce2O3 was observed after exposure in dry methane reforming conditions with low inlet CH4/CO2 ratio (1.0/0.3). The intrinsic reaction kinetics of 8% CeO2 doped Ni/Al2O3 was studied by varying inlet CH4 and CO2 concentrations, and by adding H2 and CO to the system at different temperatures. The dry reforming rate increased with increasing methane partial pressure and the operating temperature. The reaction orders in methane were always closed to 1.0 in all conditions. Carbon dioxide also presented weak positive impact on the methane conversion, whereas adding of carbon monoxide and hydrogen inhibited the reforming rate.