Operando DRIFTS and DFT Study of Propane Dehydrogenation over Solid- and Liquid-Supported GaxPty Catalysts

Supported catalytically active liquid metal solutions (SCALMS) represent a class of catalytic materials that have only recently been developed, but have already proven to be highly active, e.g., for dehydrogenation reactions. Previous studies attributed the catalytic activity to isolated noble metal atoms at the surface of a liquid and inert Ga matrix. In this study, we apply diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) with CO as a probe molecule to Ga/Al₂O₃, Pt/Al₂O₃, and Ga₃₇Pt/Al₂O₃ catalysts, to investigate in detail the nature of the active Pt species. Comparison of CO adsorption on Pt/Al₂O₃ and Ga₃₇Pt/Al₂O₃ shows that isolated Pt atoms are, indeed, present at the surface of the liquid SCALMS. Combining DRIFTS with online gas chromatography (GC), we investigated the Ga/Al₂O₃, Pt/Al₂O₃, and Ga₃₇Pt/Al₂O₃ systems under operando conditions during propane dehydrogenation in CO/propane and in Ar/propane. We find that the Pt/Al₂O₃ sample is rapidly poisoned by CO adsorption and coke, whereas propane dehydrogenation over Ga₃₇Pt/Al₂O₃ SCALMS leads to higher conversion with no indication of poisoning effects. We show under operando conditions that isolated Pt atoms are present at the surface of SCALMS during the dehydrogenation reaction. IR spectra and density-functional theory (DFT) suggest that both the Ga matrix and the presence of coadsorbates alter the electronic properties of the surface Pt species.