Structure dynamics at catalyst surfaces

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We studied the catalytically active structure, its structural transformation and dynamics, and reaction mechanism for direct phenol synthesis from benzene and molecular oxygen on a novel N-interstitial Re_<10>-cluster catalyst supported on HZSM-5 zeolite, which exhibited remarkable performances for the direct phenol synthesis. The active N-interstitial Re_<10> cluster was produced by NH_3 and it was the active species for the direct phenol synthesis using O_2 as an oxidant. Molecular oxygen (O_2) was suggested to directly react with benzene without dissociation to atomic oxygen (Ea (activation energy) = 24 kJ mol^<-1>) and the active Re cluster dynamically converted to inactive Re monomers under the reaction conditions. The structural transformation between the Re cluster and the Re monomers cycled during the phenol synthesis, whose mechanism was studied by in-situ time-resolved XAFS techniques.TiO_2 is a typical functional metal oxide which exhibits photocatalysis. Usually only ultraviolet light must be used for photochemical reactions on TiO_2 because of its bulk band gap. However, we discovered visible light photo-oxidation reactions of formic acid on the ordered lattice-work structure of a TiO_2(001) surface by using scanning tunneling microscopy (STM). Two photon photoelectron and electron energy loss spectroscopies and density functional theory calculations revealed that the nanostructured surface makes the band gap significantly smaller than 3.0 eV only at the surface layer and that the surface state of the crystal enables visible light response.