(560hn) Reactions of Methyl and Ethyl Fragments on ?-Cr2O3(101¯2)

Authors: 
Chen, H., Virginia Tech
The reaction of methyl and ethyl fragments formed by the dissociative adsorption of methyl iodide and ethyl chloride, respectively, has been examined on the non-reducible α-Cr2O3(101‾2) surface. XPS indicates that ethyl fragments bind at surface cation sites while methyl fragments can bind at either a surface cation or anion site. TPD results show that the rate-limiting step for ethyl decomposition is β-hydrogen elimination to produce ethylene directly and ethane via a subsequent ethyl hydrogenation step. Methyl fragments decompose to methylene via a rate-limiting α-hydrogen elimination step. Methane and ethylene are the primary products, with methane formed by hydrogenation of surface methyl, and ethylene formed both by methylene coupling and methylene insertion into the methyl surface bond to form an ethyl fragment that reacts via β-hydrogen elimination. Density functional theory (DFT) and DFT+U simulations were also conducted to examine the adsorption sites and calculate these reaction barriers. DFT gives a better representation of the adsorption site and the activation barriers to reaction for the rate limiting steps in contrast to the prevailing narrative that DFT+U performs better for transition metal oxide surfaces with highly-correlated electronic structures.