Bridging the Pressure Gap in the Surface Analysis of Transition Metal Catalyzed Reactions

All catalyzed reactions occur on catalyst surfaces. Surface sensitive analytical techniques provide vital information for the understanding of the catalytic processes. However, surface analysis methods often require ultrahigh vacuum (UHV). UHV conditions are ideal for fundamental research; however, industrial process occur at or above ambient pressures (AP). To better understand industrial processes, ambient pressure surface analysis methods have been developed. Using reflection absorption infrared spectroscopy (RAIRS) and its ambient pressure derivative, polarization dependent reflection absorption infrared spectroscopy (PD-RAIRS), adsorbate-surface interactions can be probed under a wide range of pressures from 1×10-10 Torr to ambient pressures. Through PD-RAIRS, gas phase reactions can be monitored quantitatively to determine the efficiency and lifetime of a catalyst as well as the kinetic parameters of the reaction. Furthermore, single atom alloy catalysts have recently garnered much attention due to the enhanced selectivity and lower energy barriers required for desired reactions to occur. PD-RAIRS was used to probe the hydrogenation of propyne to propene over a Cu(111) catalyst surface and a 2% Pd/Cu(111) single atom alloy catalyst surface. Through PD-RAIRS, the adsorption geometry of propyne on both surfaces was determined to be di-σ/di-π under ambient pressures. The adsorption geometry of propyne on Cu(111) is the same under ambient pressures and UHV conditions. Conversely, there is a stark difference in the adsorption geometry of propene between UHV and ambient pressure conditions. From the gas phase PD-RAIR spectra, the activation energy of propyne hydrogenation over the SAA catalyst was determined to be 39.4 kJ/mol which is nearly identical to the activation energy of propyne hydrogenation over a pure Pd catalyst. The turnover frequency of propene production from the single atom alloy catalyst was determined to be 33.2 s-1 at 383 K with a catalyst lifetime exceeding 12 hours at 383 K. Through ambient pressure surface analysis methods, industrial reactions are better understood. Through this understanding, industrial processes can be optimized for efficiency, throughput, and cost and waste minimization with the inclusion of single atom alloy catalysts.