Role of lattice oxygen in oxidative steam reforming of toluene as a tar model compound over Ni/La0.8Sr0.2AlO3 catalyst

Abstract

Catalytic steam reforming of tar with toluene as a model compound for production of synthesis gas (H₂ and CO) was studied using Ni/LaAlO₃, Ni/La_0.8Sr_0.2AlO₃, Ni/La₂O₃, and Ni/α-Al₂O₃ catalysts prepared using a wet impregnation method. The Ni/La_0.8Sr_0.2AlO₃ catalyst demonstrated the most superior catalytic performance in terms of both catalytic activity and coke resistance in the steam reforming of toluene. The presence of gas phase oxygen enhanced the catalytic performance of all four catalysts, with the extent of improvement being the greatest over the Ni/La_0.8Sr_0.2AlO₃ catalyst. Catalyst characterization by X-ray diffraction (XRD), temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption of oxygen (TPD-O₂) revealed that the superior catalytic performance of the Ni/La_0.8Sr_0.2AlO₃ catalyst was a result of lattice distortion caused by strontium doping, which produced a higher concentration of oxygen vacancies on the catalyst surface. This lowered the activation energy of the migration of lattice oxygen, enhancing the mobility of lattice oxygen species, and also improved the adsorption abilities of gas phase oxygen species. Mobile lattice oxygen species (O_lattice) favored the direct partial oxidation of toluene, whereas gas-phase oxygen possessed stronger oxidative abilities and favored the complete oxidation of toluene. Both mobile lattice oxygen and gas phase oxygen species actively suppressed coke formation and oxidized coke deposited on the catalyst surface, conferring coking resistance.