The Reaction Of Small Molecules On Cu₂O, Ag₂O, And Au₂O Surfaces:A Density Functional Theory Study

In order to better understand the interaction and reaction mechanism of small molecule and design catalysts, the selective oxidation reaction of vinyl chloride(VC) molecule on Cu2O(100), Ag2O(100), and Au2O(100) surfaces, formic acid decomposition on Cu2O(111), Ag2O(111), and Au2O(111) surfaces and water dissociation on Cu2O(111), Ag2O(111), and Au2O(111) surfaces have been investigated by using the density functional theory in the present paper. The main conclusions obtained from this work are summarized as follows:(1) The rate constant of VC selective oxidation on Cu2O(100), Ag2O(100), and Au2O(100) surfaces is in the order k(Ag2O)> k(Au2O)> k(Cu2O), and the chloroethylene epoxide(CE) and chloroacetadehyde(CA) are the main products on the Ag2O(100) surface at typical catalytic conditions (e.g.,500 K); on the Cu2O(100) surface, CA is the main product; on the Au2O(100) surface, CA is the main product, and some CE may be obtained.(2) Formic acid can first decompose into the reactive intermediate bidentate HCOO (bi-HCOO) on Cu2O(111), Ag2O(111), and Au2O(111) surfaces easily. Then, the formation of CO2 from monodentate HCOO (mono-HCOO), which is the isomer of bi-HCOO, is easier than that from bi-HCOO. The highest activation energy of HCOOH decomposition is the bi-HCOO rearranges to mono-HCOO, which the activation energy is in the order:Ag2O(111) (0.90 eV) > Cu2O(111) (0.80 eV)> Au2O(111) (0.73 eV).(3) On Cu2O(111), Ag2O(111), and Au2O(111) surfaces, for the first dehydrogenation step of H2O, the activation energy on the Au2O(111) surface is the lowest, but on the Ag2O(111) surface is the highest. The dehydrogenation steps of OH group on Cu2O(111), Ag2O(111), and Au2O(111) surfaces need to over a high activation barrier, which is much higher than that of the first dehydrogenation step of H2O.