Department of Inorganic Chemistry, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin (Deutschland) http://www.fhi-berlin.mpg.de/
Angew Chem Int Ed Engl. 2013 Dec 16;52(51):13553-7. doi: 10.1002/anie.201306620. Epub 2013 Nov 20.
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.
高度分散的负载在介孔硅 SBA-15 上的氧化钼通过阴离子交换制备，得到一系列具有不同钼密度（0.2-2.5 Mo 原子/nm(-2)）的催化剂。X 射线吸收、紫外可见、拉曼和红外光谱表明，在所有负载下，双锚定的四面体型二氧代 MoO4 单元是主要的表面物种。通过程序升温还原法测量，在接近单层负载的情况下，还原性能更高，在负载 8%的 Mo 时，丙烯的复分解和丙烷的氧化脱氢反应的催化活性急剧增加，这归因于 Mo 氧化物表面物种和横向相互作用的受阻。基于 DFT 计算，高负载下的 O-K 边 NEXAFS 光谱用扭曲的 MoO4 配合物解释。在高负载下，锚定硅醇基团的有限可用性迫使 MoO4 基团形成更紧张的构型。应变的发生与反应性的增加有关。
