Mechanisms of Surface Hydrogenation Reactions

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Many metal surfaces can catalyze important chemical reactions. However, metals with the highest catalytic activity are oftentimes some of the rarest and most expensive elements, such as palladium (Pd) and platinum (Pt). With support from the Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, Professor Michael Trenary of the University of Illinois at Chicago is exploring a new class of bimetallic surfaces where isolated atoms of catalytically active metals (e.g. Pd) are placed on a less expensive metal, such as copper (Cu). When these single atom alloys (SSAs) are exposed to hydrogen gas (H2), the Pd atoms dissociate the H2 molecules into H atoms, which spillover onto the Cu surface. Working with his students, Professor Trenary is using sophisticated spectroscopies to study hydrogenation reactions between the weakly bound H atoms on the surface and small organic molecules. The project could advance our understanding of catalytic hydrogenation reactions, and could lead to the development of new catalytic materials that minimize the use of expensive metals. The project is also training future scientist and fostering international cooperation through collaboration with researchers in Japan.The project is using polarization dependent reflection absorption infrared spectroscopy (RAIRS) under ambient pressure conditions to characterize the fundamental steps of hydrogenation reactions. Through analysis of the infrared spectra, Professor Trenary and his students monitor the evolution of gas phase products while also characterizing adsorbed surface species. The methodology is applied to the selective hydrogenation of acrolein to 2-propenol over a Pd-Ag(111) SAA and to CO2 hydrogenation over Pd-Cu(111) and Pt-Cu(111) SAAs. In addition to RAIRS experiments, the properties of the surfaces and their hydrogenation chemistry are being studied with a variety of other techniques including temperature programmed reaction spectroscopy (TPRS), Auger electron spectroscopy (AES), and scanning tunneling microscopy (STM). For each hydrogenation reaction, the objective is to obtain information on the identity of reaction intermediates and to distinguish them from spectator species.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.