Impact of Transition Metal Carbide and Nitride Supports on the Electronic Structure of Thin Platinum Overlayers

Atomically thin platinum (Pt) shells on titanium tungsten carbide (TiWC) and titanium tungsten nitride (TiWN) core nanoparticles display substantially modified catalytic performance compared to commercial Pt nanoparticles. In situ X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses indicate these differences are primarily caused by ligand effects from the hybridization of Pt and W d states at the core-shell interface. The heterometallic bonding between the shell and the core elements leads to broadening of the Pt valence d-band, a downshift of the d-band center, and greatly reduced adsorbate binding energies, as verified by density functional theory calculations and microcalorimetry of CO adsorption. In situ XANES measurements during reduction treatment demonstrated how surface oxides disrupt the bonding interactions between Pt and W. Changes to the Pt electronic structure from different core materials correlated with ethylene hydrogenation reactivity, where increased Pt d-band broadening was associated with weaker adsorbate binding and consequently lower turnover frequency. The significant electronic structure modification of Pt by the TiWC and TiWN cores exemplifies how core-shell nanoparticle architectures can be used to tune catalyst reactivity.