Surface tuning of noble metal doped perovskite oxide by synergistic effect of thermal treatment and acid etching: A new path to high-performance catalysts for methane combustion

Perovskite oxides containing noble metals have been widely used as heterogeneous catalysts for a broad range of important chemical reactions in recent decades, especially in environmental catalysis. However, it is still a great challenge to develop a facile strategy for tuning the distribution of noble metal on the perovskite oxide to prepare a perovskite catalyst with unexpected catalytic performance. Herein, we proposed a new path to tune the distribution of noble metal on the perovskite oxide by synergistic effect of thermal treatment and acid etching. After calcining at high temperatures (800/900 °C vs 500/700 °C), those Pd species on the LaAl0.9Pd0.1O3 catalyst would gradually exsolve from the bulk phase to the surface and subsurface of the catalyst, which was confirmed by X-ray diffraction (XRD), Raman spectra, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and CO-pulse experiment. These in situ-generated Pd species on the surface and subsurface of the catalyst can significantly improve the redox property of the LaAl0.9Pd0.1O3 catalyst. As a result, unexpected low-temperature catalytic activity and remarkable high stability for CH4 combustion were achieved on the LaAl0.9Pd0.1O3 catalyst. On this basis, the surface composition of the LaAl0.9Pd0.1O3 catalyst was further modulated by HNO3 etching. Part of the La element can be selectively etched away from the LaAl0.9Pd0.1O3 framework, and more Pd-site terminated perovskite surfaces are created after acid treatment, leading to the further promotion of catalytic activity of the LaAl0.9Pd0.1O3 catalyst for CH4 combustion.