Remarkable Pd/SnO2 nano-rod catalysts with ultra-low Pd content for toluene combustion: Clarifying the effect of SnO2 morphology on the valence states of the supported Pd species and the vital role of Pd0

Abstract

To develop efficient Pd/SnO2 catalysts with ultra-low Pd loadings for toluene combustion, nano-rod (SnO2-R) and nano-particle (SnO2-P) supports have been intentionally prepared. SnO2-P has a much larger surface area and lower crystallinity than SnO2-R, hence possessing richer surface-active O22- and O2- sites. HRTEM and XPS demonstrate that only Pd2+ is formed on Pd/SnO2-P. In contrast, a considerable amount of Pd0 is formed besides Pd2+ over Pd/SnO2-R, which is highly effective to adsorb/activate both toluene and O2 molecules. It was discovered that surface Pd0 plays a more critical role than the active oxygen sites. Therefore, Pd/SnO2-R demonstrates much higher activity than Pd/SnO2-P at the same Pd loading. With SnO2-R support, 9 times less Pd could be used to get a catalyst with rival activity than with SnO2-P. The reported results might shed some new lights for people to design highly efficient catalysts with ultra-low noble metal contents.