Screening of Bimetallic Heterogeneous Nanoparticle Catalysts for Arene Hydrogenation Activity under Ambient Conditions

This study focuses on the application of a simple screening approach to prepare and test heterogeneous mono- and bimetallic nanoparticle (NP) catalysts for arene hydrogenation activity under ambient conditions in a quick and time efficient manner, as well as detailed testing and characterization of identified active catalysts. Over 90 mono- and bimetallic NP catalysts supported on alumina were efficiently screened for arene hydrogenation activity under ambient conditions using toluene as a model substrate. Through this approach, four catalysts were determined to be active: RhPt/Al2O3, RuPt/Al2O3, IrRh/Al2O3, and IrRh/Al2O3. These catalysts were further synthesized and tested in bulk, and RhPt/Al2O3 was confirmed to be the catalyst with the highest observed rate of all the bimetallic combinations screened. Further studies were then performed, and the metal loading, temperature, pressure, and substrate to metal ratios were varied to determine the effects of these variables on the activity of the RhPt/Al2O3 catalyst and a CS2 poisoning study was performed on this catalyst to determine the number of active sites. From the temperature studies, the activation energy was calculated to be 30.4 kJ/mol, which is moderate when compared to other arene hydrogenation catalysts (42.0 kJ/mol for the hydrogenation of toluene with Ru NPs, (1) and 34.7 and 45.6 kJ/mol for benzene hydrogenation with cuboctahedral and cubic Pt NPs, respectively, (2) have been reported). Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) surface area measurements were used to characterize the active catalysts, where it was observed that very small zero oxidation state metal NPs were well dispersed throughout the high-surface area alumina support.