Impact of platinum loading and dispersion on the catalytic activity of Pt/SnO2 and Pt/α-Fe2O3

Abstract

The Pt/SnO2 (SP-samples) and Pt/α-Fe2O3 (FP-samples) with platinum loadings between 1 and 10 mol% were synthesized mechanochemically starting from platinum(II) acetylacetonate dissolved in toluene and from SnO2 and α-Fe2O3 powders obtained from tin(II) and iron(II) acetates. The STEM results show that the ultrasmall platinum nanoparticles (PtNPs) are well dispersed on the SnO2 and α-Fe2O3 supports. The PtNPs size distributions calculated with lognormal functions ranged from 1.0 to 1.3 nm. The results of temperature programmed reduction in hydrogen showed maxima at 120–160 °C due to the reduction of PtOx to Pt0. The Pt-4f-XPS results showed that the dispersed platinum on the SnO2 and α-Fe2O3 supports consisted of all three oxidation states of platinum: Pt4+, Pt2+ and Pt0. The average oxidation state of platinum as a function of molar fraction of Pt loading in the SP samples varies from 1.69 to 2.11, whereas the oxidation state of Pt in the FP samples varies more linearly and steeply from 1.42 to 2.58. The synthesized samples showed high catalytic activity for the reduction of 4-nitropenol (4-NP) to 4-aminophenol (4-AP), which can be explained by the high dispersion of non-aggregated ultrasmall PtNPs with a size of about 1 nm on the SnOx and FeOx supports.