(513es) Insights into the Electronic Structure of Catalytically-Relevant Platinum Compounds Using X-Ray Emission Spectroscopy

Platinum has the ability to catalyze a wide range of chemical reactions.^1,2 The structure and nuclearity of these catalysts are known to control their reactivity³, making rational catalyst design a tantalizing possibility. To fully exploit this potential, it is critical to understand catalyst structure—and changes—under operando conditions. This requires spectroscopic investigation, and one promising technique is valence-to-core x-ray emission spectroscopy (VtC XES). VtC XES uses hard x-ray photons to ionize core electrons on the platinum atom and then analyzes the fluorescence created when valence electrons fill the core holes.

XES spectra of 15 platinum compounds were collected at the PIPOXS beamline at CHESS (ID2A). The incident beam was energy selected using a Si(111) monochromator and focused to a spot of ~100x100 μm. The samples were excited above the Pt L3 edge and the emission signal collected using the Si(844) reflections of 5 analyzer crystals aligned on a Rowland circle⁴ and a Pilatus detector.

The compounds were selected to cover a wide range of oxidation states of the platinum center, size and nature of the ligands, and geometry. Two important emission lines appear on the spectra: Lβ_2,15 (4d->2p_3/2) and valence-to-core (Lβ₅ = 5d->2p_3/2). The Lβ₅ lines show differences in energy and intensity distribution not only for different oxidation states of the platinum center, but also for different ligand identities. These results indicate that X-ray emission spectroscopy offers insight into the electronic structure of platinum compounds and offers the potential to better understand the breaking and forming of bonds occurring during catalytic reactions.

1 R. Peng et al. Appl. Catal. B Environ., 2018, 220, 462–470

2 M. Cao et al. J. Nanoparticle Res., 2011, 13, 5147–5156

3 L. DeRita et al. Nat. Mater., 2019, 18, 746–751

4 M. Stepanenko, Plasma Devices Oper., 2009, 17, 191–200