Catalytic steam reforming of ethane and propane over CeO 2-doped Ni/Al 2O 3 at SOFC temperature: Improvement of resistance toward carbon formation by the redox property of doping CeO 2

Abstract

Ni/Al 2O 3 with the doping of CeO 2 was found to have useful activity to reform ethane and propane with steam under Solid Oxide Fuel Cells (SOFCs) conditions, 700–900 °C. CeO 2-doped Ni/Al 2O 3 with 14% ceria doping content showed the best reforming activity among those with the ceria content between 0 and 20%. The amount of carbon formation decreased with increasing Ce content. However, Ni was easily oxidized when more than 16% of ceria was doped. Compared to conventional Ni/Al 2O 3, 14%CeO 2-doped Ni/Al 2O 3 provides significantly higher reforming reactivity and resistance toward carbon deposition. These enhancements are mainly due to the influence of the redox properties of doped ceria. Regarding the temperature programmed reduction experiments (TPR-1), the redox properties and the oxygen storage capacity (OSC) for the catalysts increased with increasing Ce doping content. In addition, it was also proven in the present work that the redox of these catalysts are reversible, according to the temperature programmed oxidation (TPO) and the second time temperature programmed reduction (TPR-2) results. During the reforming process, in addition to the reactions on Ni surface, the gas–solid reactions between the gaseous components presented in the system (C 2H 6, C 3H 8, C 2H 4, CH 4, CO 2, CO, H 2O, and H 2) and the lattice oxygen (O x ) on ceria surface also take place. The reactions of adsorbed surface hydrocarbons with the lattice oxygen (O x ) on ceria surface (C n H m +O x → nCO+ m/2(H 2)+O x− n ) can prevent the formation of carbon species on Ni surface from hydrocarbons decomposition reaction (C n H m ⇔ nC+ m/2H 2). Moreover, the formation of carbon via Boudard reaction (2CO⇔CO 2+C) is also reduced by the gas–solid reaction of carbon monoxide (produced from steam reforming) with the lattice oxygen (CO+O x ⇔CO 2+O x−1 ).