Effect of steam and carbon dioxide pretreatments on methane decomposition and carbon gasification over doped-ceria supported nickel catalyst

Effects of steam (H2O) and carbon dioxide (CO2) pretreatments on methane (CH4) decomposition and carbon gasification over doped-ceria supported nickel catalysts have been studied from 400 to 500 degrees C. The doped ceria employed were gadolinia-doped ceria and samaria-doped ceria. Results indicate that a drastic increase of both H2O and CO2 dissociation activities occurs as the temperature increases from 450 to 500 degrees C. The formation of the surface hydroxyl species during H2O treatment inhibits the followed CH4 decomposition. CO but no CO2 was formed during CH4 reaction after H2O treatment. Carbon deposition during CH4 decomposition is quite large but can be removed via gasification with afterward CO2 treatment. However, some of the deposited carbon species is in a form which can not be removed with CO2 treatment but can be removed with O-2 treatment. And, higher values of the oxygen-ion conductivity and the density of the surface oxygen vacancies lead to higher activities for all dissociation and decomposition reactions.