Search

Catalytic activity of perovskites for oxygen reduction (ORR) was recently correlated with bulk d-electron occupancy of the transition metal. We expand on the resultant model, which successfully reproduces the high activity of LaMnO3 relative to other perovskites, by addressing catalyst surface morphology as an important aspect of the optimal ORR catalyst. The nature of reaction sites on low index surfaces of orthorhombic (Pnma) LaMnO3 is established from First Principles. The adsorption of O2 is markedly influenced by local geometry and strong electron correlation. Only one of the six reactions sites that result from experimentally confirmed symmetry-breaking Jahn-Teller distortions is found to bind O2 with an intermediate binding energy while facilitating the formation of superoxide, an important ORR intermediate in alkaline media. As demonstrated here for LaMnO3, rational design of the catalyst morphology to promote specific active sites is a highly effective optimization strategy for advanced functional ORR catalysts. © 2015 American Chemical Society.

Platinum(II) and palladium(II) complexes [M(CH₃)(L)]SbF₆ with substituted terpyridine ligands L undergo light-driven oxygen insertion reactions into metal methyl bonds resulting in methylperoxo complexes [M(OOCH₃)(L)]SbF₆. The oxygen insertion reactions occur readily for complexes with methyl ligands that are activated due to steric interaction with substituents (NH₂, NHMe or CH₃) at the 6,6″-positions on the terpyridine ligand. All complexes exhibit attractive intermolecular π···π or M···M interactions in the solid state and in solution, which lead to excited triplet dinuclear M–M complexes upon irradiation. A mechanism is proposed whereby a dinuclear intermediate is generated upon irradiation that has a weakened M–C bond in the excited state, resulting in the observed oxygen insertion reactions.

The preparation of chiral metal complexes in NaY zeolite is reported. The guests, chiral metal complexes, were entrapped in the supercages of NaY zeolite (host) by a two-step process in the liquid phase: (i) inclusion of the selected transition metal (rhodium(III) and manganese(II)) by ion-exchange in the porous structure and (ii) introduction of the chiral ligand, an D-erythrose amino derivative, namely (2R,4S,5R)-4-[(N-methylamino)methyl]-2-phenyl-1,3-dioxan-5-ol, followed by assembly of the complex inside the void space of the zeolite. Structural (FTIR and XRD), surface studies (SEM) and chemical analyses were used to characterize the new host guest catalysts and the results indicated that chiral metal complexes were successfully encapsulated in supercages of the NaY zeolite. Catalytic studies were performed in liquid phase for norbornene oxidation using tert-butyl hydroperoxide as the oxygen source. The catalytic results were compared with styrene and cyclohexanol oxidation as model reactions. The prepared chiral catalysts exhibited catalytic activity for all oxidation reactions. The stability of the catalysts before and after reaction was confirmed by cyclic voltammetry and FTIR studies., The authors thank Dr. M. F. R. Pereira for support in the TGA analysis. I.K.B., A.R.S., and C.O. thank the Foundation for the Science and Technology (FCT, Portugal), for the contract under "Programa Ciencia 2007 e 2008". A.R.S. also thanks FCT for the contract under "Investigador FCT 2012" and I.K.B. also is thankful for the contract under the project NORTE-07-0124-FEDER-000039. The authors thank the FCT and FEDER-COMPETE-QREN-EU for financial support to the Research Centers, CQ/UM, PEst-C/QUI/UI0686/2013 (F-COMP-01-0124-FEDER-037302), the project NORTE-07-0124-FEDER-000039, the NMR Portuguese network (PTNMR, Bruker Avance III 400-University Minho), and CICECO/UA (Pest-C/CTM/LA0011/2013)., info:eu-repo/semantics/publishedVersion

Pyrrole was polymerized electrochemically in an aqueous medium on a platinum electrode in the presence of a polyanion, containing covalently bound flavin units. Depending on the applied potential the polypyrrole-films thus formed were powdery and non-adherent (V 1000 mV). Besides the applied potential, medium pH and added low molar mass salt influenced the morphology and composition of the PPy-layer. The flavin-containing polyanion was incorporated in the film as a dopant. Depending on the medium pH and amount of low molar mass salt added, the film formed by this method contained various amounts of polymer-bound flavin. Cyclic voltammograms confirmed the presence of electrochemically active flavin in the layer. The oxidation of 1-benzyl-1,4-dihydronicotinamide (BNAH) was used as a model reaction to test the catalytic activity of the immobilized flavin. The modified electrode showed fast current response on addition of BNAH, not only at an applied potential of 0.9 V (oxidation of H2O2) but also in the absence of oxygen at 0.3 V. This might indicate that a direct transfer of electrons takes place between the flavin units and the (PPy-)electrode. Cycling of the PPy-film through its reduced and oxidized state does not lead to any loss of the flavin containing polyanion. In the case of low molar mass flavin-containing dopants most of the flavin is released from the film upon reduction of the PPy.