Reductive Treatment of Ga–Pt-Supported Catalytically Active Liquid Metal Solutions (SCALMS) for Propane Dehydrogenation

A comprehensive investigation of the impact of hydrogen (H2) pretreatments on Ga-Pt supported catalytic active liquid metal solution (SCALMS) for propane dehydrogenation (PDH) is reported. Our approach bridges from model system investigations to real-world catalytic systems, which are tested in continuously operating PDH reactors. The microscopic and spectroscopic findings on model Ga-Pt systems suggest changes in the electronic structure and surface chemistry during SCALMS sample oxidation and H2 pretreatment, indicating potential modifications of the active sites involved in PDH. H2 pretreatments of technical Ga-Pt SCALMS prepared by ultrasonication (US) led to significantly improved activity, i.e., the conversion of propane increased from 10% for the untreated catalyst to 26% for the H2 pretreated (5 h at 823 K) catalyst. We attribute this enhanced activity to the removal of a gallium oxide (GaO x ) shell, as confirmed by synchrotron-based in situ X-ray photoelectron spectroscopy (XPS) as well as in situ transmission electron microscopy (TEM) investigations of Ga-Pt model alloys. These findings are supported by density functional theory (DFT) and machine learned force field (ML-FF) calculations. Increasing the temperature of the H2 treatment to 923 K reduced the deactivation rate of the catalyst to as low as 0.01 h-1, which is 3 times more stable than what was observed for the untreated catalyst. This deactivation is ascribed to bulk restructuring of the alloy, leading to the formation of less active Pt species as confirmed by spectroscopic and microscopic analysis. Our work not only elucidates the fundamental properties, i.e., typology, electronic structure, and reactivity, of isolated Pt atoms in Ga-Pt SCALMS but also proposes underlying mechanisms for the activation and deactivation of PDH catalysts.