Atmospheric Chemistry Program Seminar
Role of the Metal Support Interface in H2 Activation on Supported Gold Nanoparticles
Alexander Bradley, ANYL 1st year student
"Global Hydrogen production exceeds 50 million tons per year, largely for the production of ammonia. Given its importance, a fundamental understanding of hydrogen activation is vital when designing new catalysts. Hydrogen activation on gold catalysts is poorly understood and understudied, and the weak adsorption effects allow only a few types of experimental measurements. We have developed a kinetic model for analyzing hydrogen binding parameters on gold, and a method for extracting a proposed mechanism.
Hydrogen is thought to activate homolytically on late transition metals, but recent evidence suggests that it activates heterolytically at the metal-support interface of supported gold catalysts. The thermodynamic properties of this reaction were calculated by Van’t Hoff analysis. Enthalpy and entropy terms were found to be much lower than popular supported metals (Ni, Rh, etc). Kinetic Isotope Effect (KIE) experiments were carried out to determine the nature of the hydrogen activation, and whether the mechanism includes a proton coupled electron transfer (PCET) step."
Theoretical Examination of Isoprene’s Behavior at the Air-Water Interface
Kyle McMillan, ANYL 1st year student
"Isoprene is the most widely emitted biogenic hydrocarbon in the atmosphere (approximately 500 Tg emitted annually), making it a significant player in atmospheric chemistry. So far, most research concerning isoprene’s role in the atmosphere has examined its gas-phase chemistry with little consideration given to its potentially significant chemistry within clouds. The purpose of this study was to elucidate isoprene’s behavior at the air-water interface of a water droplet. To do this, high level molecular dynamics (MD) calculations were utilized to simulate isoprene’s interaction with a droplet of 10-nm diameter. The data generated by these calculations were then used to describe both isoprene’s conformational dynamics and chemical group orientations at the air-water interface, looking closely at the torsion angles of both its s-trans and s-gauche conformers as well as the distances between each of its atoms and the water molecules comprising the water droplet. Though the results of this study were not wholly conclusive, due primarily to incomplete datasets generated by the MD calculations, there were some indications of potentially favorable interactions of isoprene with the air-water interface, especially for its s-gauche conformer. Should the air-water interface selectively alter the chemical properties of either of isoprene’s two major conformers (for example, by augmenting the reactivity of either toward a major atmospheric oxidant such as OH) this would have clear implications for isoprene’s chemistry in the troposphere, which has been shown to vary significantly with conformational state."