Electrochemical Partial Oxidation of Alkenes: Understanding Selectivity and Reaction Mechanisms

Abstract

With a deepening electrification of society, electrochemical conversion from one chemical to another will be essential for the chemical plants of the future. While there is intense focus on reduction reactions (i.e. CO2, water, N2), partial oxidation reactions have been relatively underinvestigated. This talk will discuss our recent work on electrochemical partial oxidation of propene. With propene having both a double bond and an allylic carbon, this is an optimal test molecule to create a broad spectrum of products following a variety of mechanisms. By using a Pd catalyst, we were able to produce acrolein, acrylic acid, allyl alcohol, propylene glycol, acetone with only small amounts of CO2 formation. Variations is oxidation potential allowed us to see changes in product distribution, which we then used to theorize potential reaction mechanisms. With acrolein being one of our largest products, this meant the allylic carbon was oxidized rather the double bond. DFT calculations showed that the acrolein mechanism was feasible, provided surface coverage of other species (oxygen species and flat lying propene) dominated the surface coverage, thus allowing for a small amount of allylic carbon to bind to the surface due to steric advantages. Electrochemical Sniffer Chip technology (1) was then used to measure submonolayer gas absorption/desorption as a function of electrochemical potential, which provided supporting evidence to the aforementioned mechanism. The talk will show our process in analyzing this reaction and mechanisms as well as how these discoveries are applicable to the broader field of partial oxidation reactions. (1) Trimarco, D. et. al, Review of Scientific Instruments 86, 075006 (2015) Figure 1