We report results of first principle d. functional calcns. on the catalytic activity of isolated Pd atoms deposited on different MgO surface sites. The reaction of interest is the cyclization of acetylene to benzene, 3C2H2 → C6H6. Exptl., it has been obsd. that the reaction is catalyzed by size-selected Pd clusters and that even a single Pd atom deposited on MgO is enough for the reaction to occur. In this theor. study we have analyzed in detail the role of the support. It is found that a gas-phase Pd atom is not active in promoting the reaction as it has not enough electron d. to bind and activate three acetylene mols. The reaction, however, occurs when Pd is bonded to low-coordinated oxygen anions of the surface, located at sites such as steps and corners. Oxygen anions on (001) terraces, in fact, are not a sufficiently good electron donor to increase the electron d. on the metal. Another group of surface defects which play a role in the activation of the Pd atom are F centers, oxygen vacancies with two trapped electrons. These defect centers, independently of their location, terrace, edge, or corner, are very strong "basic" sites: they efficiently transfer electronic charge to the adsorbed metal atom and thus improve its catalytic properties. This study demonstrates the importance of morphol. defects and anion vacancies at the metal-oxide interface and the noninnocent role of the substrate in catalysis by supported metal particles. [on SciFinder(R)]     «

We report results of first principle d. functional calcns. on the catalytic activity of isolated Pd atoms deposited on different MgO surface sites. The reaction of interest is the cyclization of acetylene to benzene, 3C2H2 → C6H6. Exptl., it has been obsd. that the reaction is catalyzed by size-selected Pd clusters and that even a single Pd atom deposited on MgO is enough for the reaction to occur. In this theor. study we have analyzed in detail the role of the support. It is found that a gas-...     »

Electron transfer (activation mechanism quantum-chem. study of acetylene cyclotrimerization on Pd1/MgO and the role of surface defects in the activation of supported metals) Adsorption enthalpy (of Pd quantum-chem. study of acetylene cyclotrimerization on Pd1/MgO and the role of surface defects in the activation of supported metals) Electron density (on metal vs. acetylene activation quantum-chem. study of acetylene cyclotrimerization on Pd1/MgO and the role of surface defects in the activation of supported metals) Adsorbed substances Catalyst supports Cluster model Complexation Cyclotrimerization Cyclotrimerization catalysts Density functional theory HF MO Surface basicity Surface defects (quantum-chem. study of acetylene cyclotrimerization on Pd1/MgO and the role of surface defects in the activation of supported metals) Reaction mechanism (surface quantum-chem. study of acetylene cyclotrimerization on Pd1/MgO and the role of surface defects in the activation of supported metals) surface defect acetylene cyclotrimerization palladium magnesia     «

Electron transfer (activation mechanism quantum-chem. study of acetylene cyclotrimerization on Pd1/MgO and the role of surface defects in the activation of supported metals) Adsorption enthalpy (of Pd quantum-chem. study of acetylene cyclotrimerization on Pd1/MgO and the role of surface defects in the activation of supported metals) Electron density (on metal vs. acetylene activation quantum-chem. study of acetylene cyclotrimerization on Pd1/MgO and the role of surface defects in the activation...     »

CAN 134:29051 22-5 Physical Organic Chemistry Dipartimento di Scienza dei Materiali, Universita Milano-Bicocca and Istituto Nazionale per la Fisica della Materia, Milan, Italy. Journal 1089-5647 7440-05-3 (Palladium) Role: CAT (Catalyst use), PEP (Physical, engineering or chemical process), PRP (Properties), RCT (Reactant), PROC (Process), USES (Uses), RACT (Reactant or reagent) (quantum-chem. study of acetylene cyclotrimerization on Pd1/MgO and the role of surface defects in the activation of supported metals); 1309-48-4 (Magnesia) Role: CAT (Catalyst use), PRP (Properties), USES (Uses) (quantum-chem. study of acetylene cyclotrimerization on Pd1/MgO and the role of surface defects in the activation of supported metals); 71-43-2 (Benzene) Role: FMU (Formation, unclassified), PRP (Properties), FORM (Formation, nonpreparative) (quantum-chem. study of acetylene cyclotrimerization on Pd1/MgO and the role of surface defects in the activation of supported metals); 74-86-2 (Acetylene) Role: PEP (Physical, engineering or chemical process), PRP (Properties), RCT (Reactant), PROC (Process), RACT (Reactant or reagent) (quantum-chem. study of acetylene cyclotrimerization on Pd1/MgO and the role of surface defects in the activation of supported metals)     «

CAN 134:29051 22-5 Physical Organic Chemistry Dipartimento di Scienza dei Materiali, Universita Milano-Bicocca and Istituto Nazionale per la Fisica della Materia, Milan, Italy. Journal 1089-5647 7440-05-3 (Palladium) Role: CAT (Catalyst use), PEP (Physical, engineering or chemical process), PRP (Properties), RCT (Reactant), PROC (Process), USES (Uses), RACT (Reactant or reagent) (quantum-chem. study of acetylene cyclotrimerization on Pd1/MgO and the role of surface defects in the activation of s...     »