Promotional effect of lanthana on the high-temperature thermal stability of Pt/TiO2 sulfur-resistant diesel oxidation catalysts†
In order to efficiently remove diesel exhaust pollutants during long-term application under high temperature conditions, enhancing the thermal stability of catalysts is essential. Here, lanthana was introduced into a TiO2 sulfur-resistant support via co-precipitation, and then a Pt/TiO2–La2O3 diesel oxidation catalyst (DOC) was prepared using the impregnation method. The SO2 uptake and EDX results indicate that the La2O3-doped Pt/TiO2–La2O3 catalyst displays superior sulfur resistance compared to the commercial Pt/Al2O3 and Pt–Pd/CeO2–ZrO2–Al2O3 DOC catalysts. Catalytic performance measurements showed that the as-prepared Pt/TiO2–La2O3 catalyst exhibited significantly better activity than Pt/TiO2 after high-temperature thermal aging and simulative 160 000 km vehicle aging. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and N2 adsorption–desorption results suggest that some of the La3+ dopant ions migrated to the grain boundary of the TiO2 crystal and other La3+ ions replaced Ti4+ ionic sites to form Ti–O–La bands, which impeded the crystal growth and phase transition of TiO2, and hence mitigated the destruction of the porous texture of TiO2. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) observations further demonstrate that the introduction of lanthana into TiO2 suppressed Pt particle agglomeration and catalyst particle sintering, consequently enhancing the thermal stability of the Pt/TiO2–La2O3 catalyst. Thus, this work shows that lanthana can play an extremely important role in improving the structural and textural stability of TiO2 and stabilizing the surface-active component of the Pt/TiO2 DOC catalyst, hence enhancing the high-temperature aging resistance.