Structure dynamics at catalyst surfaces

研究了以HZSM-5分子筛为载体的新型N-间隙基团簇催化剂上苯与分子氧直接合成苯酚反应的活性结构、结构转化和动力学，以及反应机理。NH_3生成的活性N-间隙Re_lt；10&Gt；团簇是以O2为氧化剂直接合成苯酚的活性物种。在该反应条件下，分子氧(O_2)直接与苯反应而不解离成原子氧(Ea(活化能)=24kJ·mol~(-1)~(-1))，活性Re原子团簇动态转化为非活性Re~(2+)。利用原位时间分辨XAFS技术研究了苯酚合成过程中Re团簇和Re单体之间的结构变化，并对其机理进行了研究。由于二氧化钛的块状带隙，通常只能用紫外光在二氧化钛上进行光化学反应。然而，我们用扫描隧道显微镜(STM)观察到了甲酸在二氧化钛(001)表面有序晶格结构上的可见光光氧化反应。双光子光电子和电子能量损失谱和密度泛函理论计算表明，纳米结构表面使带隙仅在表面层显著小于3.0 eV，并且晶体的表面态使可见光响应成为可能。

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.