Theoretical Studies of Adsorption and Reactivity at the Gas-Solid Interface

Catalytic transformations of small molecules is of great interest for both laboratory and industrial practices. Two specific transformations are ethylene to ethylene oxide and combinations of azides and alkenes into aziridine molecules. Ethylene oxide is an epoxide used as a feed-stock for many bulk reactions and commercial products such as antifreeze and various sterilization techniques, while molecules with the aziridine functional group are used for many ring opening and closing techniques as well as in pharmaceuticals and other drug treatments. For production of ethylene oxide, the combination of oxygen adsorbed onto a silver crystal is the known catalysts for thus reaction, but the actual catalytic species is unknown. In the following work, the interactions of O/Ag(111) have been modeled with a lattice-gas pairwise adsorption model. We have applied this model to Monte Carlo simulations to determine the viability of oxygen adsorbing to the surface, subsurface, and bulk regions. We hypothesize that while the existence of subsurface adsorption is difficult to experimentally determine, subsurface oxygen has different electronic and reactive characteristics than surface adsorption and plays an active role in the catalysis of ethylene to ethylene oxide. Our lattice-gas model will additionally allow us to study the known ``pressure gap" in surface science applications between ultra-high vacuum conditions of most laboratory results to the industrial (high pressure) conditions the reaction performs under. We will explore the role of subsurface adsorption under these conditions two-fold, first by modeling the direct reaction with ethylene and then by allowing oxygen to induce surface reconstructions in our simulations. We also show theoretical results for a new generation of iron-tetracarbene catalyst used for ``C₂ + N₁" aziridine of p-tolyl azide with 1-decene. Our calculations focus on the reactivity of the different substituted tolyl azides with our catalyst, and the possibility of stereoselective control.