(736a) Local Compositions and Structures of Platinum Species in Heterogeneous Catalysts

The preparations of Pt-containing heterogeneous catalysts generally involve several distinct chemical treatments (e.g., oxidation, reduction, sulfidation) that are collectively influential on the macroscopic adsorption and reaction properties of the final catalyst products. Despite the technological importance of Pt-containing catalysts and compounds, distinguishing the effects of these treatments on local and surface Pt environments is still a challenging task. This is principally due to the inherent disorder present within many heterogeneous Pt-containing materials, which present challenges to elucidating Pt moieties with standard diffraction or spectroscopy methods. Nuclear magnetic resonance (NMR) spectroscopy is a sensitive probe of local bonding environments and can in principle distinguish locally ordered and disordered molecular species. However, solid-state ¹⁹⁵Pt NMR spectra can span very large radiofrequency bandwidths (~MHz), which can provide subtle information on the molecular environments of Pt species, but have been impractical to excite and detect with standard techniques. Nevertheless, recent methodological advancements now allow such large spectral widths to be managed enabling detailed characterization of Pt species that have till now been infeasible to measure. Results will be presented for bulk, supported nanoparticle, and molecular Pt catalysts whose local ¹⁹⁵Pt environments are readily distinguished, including influences of the supports and of oxidation and sulfidation treatments. These insights are correlated with macroscopic reactions properties, which will be discussed for several examples.