Evidence for H₂-Induced Ductility in a Pt/Al₂O₃ Catalyst

Abstract

High Resolution Image Download MS PowerPoint Slide Focusing on a highly dispersed 5 wt % Pt/Al 2 O 3 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 H 2 equilibrium pressure and temperature. The INS profiles are interpreted on the basis of systematic DFT simulations on 26 different Pt x H y /γ-Al 2 O 3 models, indicating that the INS spectra are a unique fingerprint of the Pt x H y /γ-Al 2 O 3 model morphology, size ( x ), H-coverage ( y ), and typology of Pt–H species. We fit the experimental INS spectrum of Pt/Al 2 O 3 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 Pt 55 H y /γ-Al 2 O 3 clusters completely solvated by H atoms ( y = 81 and 91) and in weak interaction with the support, followed by the disordered Pt 34 H 54 /γ-Al 2 O 3 model (36%) and by the smaller Pt 13 H 32 /γ-Al 2 O 3 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 Pt x H y models in stronger interaction with the γ-Al 2 O 3 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/Al 2 O 3 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.

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