Introduction Ultrasmall platinum nanoparticles probed with synchrotron radiation have been shown to undergo partial oxidation on exposure to ambient air (Gallagher et al. Catal. Sci. Tech. 4, 2014, 3053). In this work, we have been able to more definitively characterize this behavior with high sensitivity powder XRD, XPS and STEM imaging and Fast Fourier Transform analysis. Materials and Methods Different weight loadings of Pt nanoparticles were synthesized using Strong Electrostatic Adsorption (SEA) on a series of silica and carbon supports with varying surface areas and micropore volumes. The catalysts were air exposed for upto 2 weeks and characterized using a Rigaku X-Ray Diffractometer equipped with a Si- slit detector and the results were coupled with scanning transmission electron microscopy (STEM) and fast Fourier transform (FFT) analysis to derive fundamental information on the oxidation state of platinum catalysts. Results and Discussion XRD patterns obtained using a high sensitivity solid state detector could be background-subtracted and deconvoluted to reveal platinum 2+/3+ oxide (Pt3O4) peaks for the smallest nanoparticles on both silica and carbon supports, in addition to Pt metal. PtO2 formed in addition to Pt3O4 when silica supported nanoparticles were calcined at high temperature. Small particle oxidation was confirmed with XPS. FFT analysis of atomically resolved nanoparticles supported on carbon showed that the transition to oxide takes place in the 1.6-2.7 nm; above 2.8 nm, all particles are metallic, below 1.5 nm, all are Pt3O4, and in between they consist of a core of Pt metal and shell of Pt3O4. We saw an indirect effect of carbon support microporosity on nanoparticle oxidation. At high metal loadings via SEA, larger nanoparticles formed upon reduction in highly microporous supports, probably due to increased precursor-precursor interaction during reduction. These were more metallic owing to their larger size.

Ambient oxidation of ultrasmall platinum nanoparticles

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.