Role of support lattice oxygen on steam reforming of toluene for hydrogen production over Ni/La_0.7Sr_0.3AlO_3-δ catalyst

Catalytic steam reforming of aromatic hydrocarbon using toluene as a model compound for hydrogen production over Ni catalyst supported on perovskite oxide was investigated. Ni/La_0.7Sr_0.3AlO_3-δ catalyst showed higher activity and lower coke formation than other Ni-supported catalysts on hydrogen production by toluene steam reforming. Transient response using H₂¹⁸O revealed that the surface lattice oxygen of La_0.7Sr_0.3AlO_3-δ worked as active oxygen by redox mechanism at 873 K. Coke deposited on the catalyst surface after the reaction was removed oxidatively by lattice oxygen in/on the perovskite support. The working temperature of the lattice oxygen depended on the catalyst support characteristics. Analyses of the support structure by XRD and XPS revealed that the lattice distortion and the increasing of oxygen vacancies by partial Sr substitution enhanced the redox ability of lattice oxygen. Arrhenius plots showed that the rate-determining step of the reaction changed at a certain temperature at which the lattice oxygen was able to contribute to reaction over Ni/La_0.7Sr_0.3AlO_3-δ and Ni/LaAlO ₃. The dependence of the reaction rate on the partial pressure of H₂O and toluene revealed that the rate-determining step might be the formation of hydroxyl group on the support surface in a lower temperature region and the adsorption of toluene on the Ni surface in a higher temperature region.