Electrochemical evidence that pyranopterin redox chemistry controls the catalysis of YedY, a mononuclear Mo enzyme

How Strain Affects the Reactivity of Surface Metal Oxide Catalysts Angewandte Chemie International Edition by Kazuhiko Amakawa, Lili Sun, Chunsheng Guo, Michael Hävecker, Pierre Kube, Israel E. Wachs, Soe Lwin, Anatoly I. Frenkel, Anitha Patlolla, Klaus Hermann, Robert Schlögl, Annette Trunschke  /  30d  //  keep unread  //  hide  //  preview Abstract Highly dispersed molybdenum oxide supported on mesoporous silica SBA-15 has been prepared by anion exchange resulting in a series of catalysts with changing Mo densities (0.2–2.5 Mo atoms nm−2). X-ray absorption, UV/Vis, Raman, and IR spectroscopy indicate that doubly anchored tetrahedral dioxo MoO4 units are the major surface species at all loadings. Higher reducibility at loadings close to the monolayer measured by temperature-programmed reduction and a steep increase in the catalytic activity observed in metathesis of propene and oxidative dehydrogenation of propane at 8 % of Mo loading are attributed to frustration of Mo oxide surface species and lateral interactions. Based on DFT calculations, NEXAFS spectra at the O-K-edge at high Mo loadings are explained by distorted MoO4 complexes. Limited availability of anchor silanol groups at high loadings forces the MoO4 groups to form more strained configurations. The occurrence of strain is linked to the increase in reactivity. Only uncomfortable seats left: At high surface coverages of molybdenum oxide, at which surface hydroxy anchoring sites are limited, surface metal oxide molecules are forced to be anchored in strained/frustrated configurations. This strain leads to increased reactivity and explains the non-linear coverage dependence sometimes observed in monolayer-type supported metal oxide catalysts. Visit Website   +TAG