Investigation of La promotion mechanism on Ni/SBA-15 catalysts in CH4 reforming with CO2

Abstract

La-promoted Ni/SBA-15 catalysts (molar ratio of La2O3/Ni=0.10, 0.25) were prepared by the wetness impregnation method for the reforming of CH4 with CO2. The La species are highly dispersed on the catalyst and cause smaller nickel particles in comparison with the Ni/SBA-15 catalyst. The presence of La in Ni/SBA-15 evidently improves the catalytic activity and stability. For the reaction mechanism study, a special infrared cell under rapid heat dissipating was designed to trap the transient intermediates (e.g., CHxO*) on the catalysts. For La–Ni/SBA-15 with La2O3/Ni=0.10, the adsorbed Ni(CO)4 and bridge-bonded CO (Ni2–CO) form on the nickel surface with large particle size, while for the one with La2O3/Ni=0.25, CHxO* (x=2, 3) surface species occur on small sized nickel particle. The results indicate that highly dispersed La effectively promotes CO2 dissociation into oxygen atom which facilitates the formation of the different C1 intermediates from the adsorbed CH4 on the neighboring nickel species depending on the varied La2O3/Ni ratio.