(616h) Structure, Stability and Activity Analysis of Metallic and Bimetallic Clusters Using Density-Functional Theory

Bimetallic catalysts synthesized using Cu and Zn/ZnO exhibit excellent performance in the glycerol hydrogenolysis reaction. It has been experimentally observed that while Cu is the active element in such catalysts, some presence of Zn/ZnO increases the catalyst stability and performance. In order to develop a theoretical understanding of the role of Zn/ZnO doping in Cu, we have performed Density Functional Theory (DFT) calculations of representative Cu-Zn/ZnO clusters of up to 10 atoms using Gaussian 09. We begin with finding minimum energy configurations of these clusters and determine their physical stability and activity with the help of average bond length, binding energy, dissociation energy, second order difference of total energy, HOMO-LUMO gap, and chemical hardness. Odd‐even alteration in properties that determine cluster stability/activity is observed with cluster size, which may be attributed to the presence/absence of unpaired electrons. The difference in behavior between Zn/ZnO doping is interpreted in terms of charge transfer between atoms. This was followed by a detailed study of the various elementary steps during the glycerol hydrogenolysis reaction, i.e., species adsorption/desorption and surface reactions: (1) decomposition of glycerol to acetol and water followed by the (2) reaction of acetol with hydrogen to 1,2-Propanediol (PDO). Through the evaluation of the transition states and the activation energy of the two reactions, the first reaction is found to be rate limiting. This study provides a detailed understanding of the influence of Zn/ZnO doping in the adsorption and reaction processes involved in the hydrogenolysis reaction. Our results shows good agreement with experimental results of this reaction and thus provides design rules of Cu-Zn/ZnO catalysts. Some results on studies performed on Cu-Zn/ZnO surfaces with MgO support using plain wave calculations in Quantum-Espresso will also be presented.