Recently, a new type of dehydrogenation catalyst was proposed, denoted as ‘supported catalytically active liquid metal solution’ (SCALMS).[1] In SCALMS, low amounts of catalytically active metals (e.g. Pd, Rh or Pt) are dissolved in Ga and dispersed on high-surface-area oxide or carbon supports. While such alloys form intermetallic compounds at high noble metal concentration, the concentrations in SCLAMS is so low that a liquid Ga-rich phase is formed under reaction conditions (300 to 400 °C). In this state, SCALMS show high selectivity and suppressed coke formation.[1] It was proposed that the active sites in SCALMS are isolated metal atoms on the surface of the inert Ga droplet. This implies that SCALMS can be considered as a new type of single atom catalyst. In the first part of this study, we characterize Pt-Ga and Rh-Ga SCALMS under operando conditions. Combining diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and online gas chromatography (GC) we correlate catalyst performance and surface sites and show that, indeed, isolated Pt atoms are exposed during dehydrogenation. IR spectra and density functional theory (DFT)[2] suggest that both, the Ga matrix and the co-adsorbates alter the electronic properties of the surface Pt. In the second part, we investigate Pd-Ga and Pt-Ga model SCALMS, prepared by physical vapor deposition of Pd/Pt and Ga in ultrahigh vacuum onto highly oriented pyrolytic graphite (HOPG). Combining atomic force microscopy (AFM) and infrared reflection absorption spectroscopy (IRAS), we investigate the growth, morphology, surface chemistry, and stability of these systems. Experimental data on the vibrational frequencies and binding energies of CO are compared to DF calculations, suggesting that the Pd sites are widely separated in the Ga matrix.

Supported catalytically active liquid metal solutions: From operando studies to model catalysis

2019 Spring National Meeting

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