Afanasiev Pavel
Institut de Recherches sur la Catalyze 2, Avenue A. Einstein, 69626 Villeurbanne Cédex, France.
J Phys Chem B. 2005 Oct 6;109(39):18293-300. doi: 10.1021/jp050554u.
Mixed Nb-Mo oxides were prepared by solid-state reaction of Nb(V) and Mo(VI) oxides at 973-1123 K. Optimal conditions were determined for the formation of the Mo3Nb2O14 compound. As established by Rietveld refinement of the powder X-ray diffraction patterns, the Mo3Nb2O14 oxide has the tetragonal cell with a = 23.150(6) A and c = 3.998(4) A and a tunnel structure similar to that of the Mo5O14 oxide. The solids were characterized by several physical techniques, including scanning and transmission electron microscopy, FT-IR, UV-visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and electron spin resonance spectroscopy. It has been shown that the Mo3Nb2O14 solid prepared in air at 973-1073 K after cooling to room temperature contains high amounts of Mo(V) species (ca. 1% of total molybdenum). The presence of paramagnetic species correlates with the intense green color of the solids and the strong d-d transition band in the UV-visible spectra, typical for the d1 species. The amount of paramagnetic species does not depend on the solid annealing and/or on the small variations of its composition. Neither is it related to the oxygen release upon the solid heating, being therefore an intrinsic property of the Mo3Nb2O14 oxide. The unusual stabilization of reduced Mo species in the highly oxidizing conditions was explained by the substitution disorder between Nb and Mo atoms. It is supposed that a configuration containing mu3 oxygen bonded to three Mo(VI) atoms is unstable and decomposes, leading to a Mo(V) center and a hole in the valence band.
通过在973 - 1123 K下Nb(V)和Mo(VI)氧化物的固态反应制备了混合铌 - 钼氧化物。确定了形成Mo3Nb2O14化合物的最佳条件。通过粉末X射线衍射图谱的Rietveld精修确定，Mo3Nb2O14氧化物具有四方晶胞，a = 23.150(6) Å，c = 3.998(4) Å，并且具有与Mo5O14氧化物类似的隧道结构。通过几种物理技术对这些固体进行了表征，包括扫描和透射电子显微镜、傅里叶变换红外光谱、紫外 - 可见漫反射光谱、X射线光电子能谱和电子自旋共振光谱。结果表明，在973 - 1073 K的空气中制备并冷却至室温后的Mo3Nb2O14固体含有大量的Mo(V)物种（约占总钼的1%）。顺磁物种的存在与固体强烈的绿色以及紫外 - 可见光谱中典型的d1物种的强d - d跃迁带相关。顺磁物种的数量不取决于固体的退火和/或其组成的微小变化。它也与固体加热时的氧释放无关，因此是Mo3Nb2O14氧化物的固有特性。在高氧化条件下还原态Mo物种的异常稳定是由Nb和Mo原子之间的取代无序来解释的。据推测，一种包含与三个Mo(VI)原子键合的μ3氧的构型是不稳定的，会分解，导致一个Mo(V)中心和价带中的一个空穴。
