Evidence for H-2-Induced Ductility in a Pt/Al2O3 Catalyst

Focusing on a highly dispersed S wt % Pt/Al2O3 catalyst for industrial hydrogenation and dehydrogenation reactions, we employ inelastic neutron scattering (INS) spectroscopy to obtain the vibrational fingerprint of the hydrogenous species formed under different H2 equilibrium pressure and temperature. The INS profiles are interpreted on the basis of systematic DFT simulations on 26 different PtxHy/gamma-Al2O3 models, indicating that the INS spectra are a unique fingerprint of the PtxHy/gamma-Al2O3 model morphology, size (x), H-coverage (y), and typology of Pt-H species. We fit the experimental INS spectrum of Pt/Al2O3 measured under higher H-coverage conditions with a linear combination of the simulated spectra. We find that 47% of the spectrum can be ascribed to Pt55Hy/gamma-Al2O3 clusters completely solvated by H atoms (y = 81 and 91) and in weak interaction with the support, followed by the disordered Pt34H54/gamma-Al2O3 model (36%) and by the smaller Pt13H32/gamma-Al2O3 one (18%). These results are in good agreement with the particle size distribution previously determined by TEM and confirmed by XAS. A second INS spectrum collected under lower H-coverage conditions exhibits the typical features of less hydrogenated PtxHy models in stronger interaction with the gamma-Al2O3 support, as well as bands associated with the formation of -OH species at the support by H-spillover. Overall, our study reveals the relevance of combined INS and DFT analysis to quantify the versatile atomic scale's properties of Pt/Al2O3 catalyst in terms of cluster morphology, size, typology of Pt-H species, and cluster/support interaction depending on the H-coverage, providing important insights about their behavior under hydrogenation conditions.