Preparation of catalysts based on unique valence and coordination state in mesoporous titania with extremely high surface area

以十二胺为介孔结构导向剂，采用醇盐直接共缩合法和后修饰法制备了以介孔TiO_2为载体的V、Ce、Mo和W催化剂，其中X=V、Ce、Mo和W。考察了载体二氧化钛的物相、X的局域结构以及催化剂上的乙醇-氧反应。在673 K下煅烧在两种催化剂中诱导新的中间相，具有比最初呈现的（2.0-2.1 nm）更大的孔径（3.2-4.6 nm）。这一阶段是不相似的任何介孔二氧化钛以前报道过。X射线衍射和拉曼光谱分析表明，Mo/mesoTiO_2在573 K和673 K分别发生了从非晶相到金红石相和从金红石相到锐钛矿相的相变。以前很少观察到随着温度的升高从金红石相到金红石相的变化。而Mo-meso TiO_2在573 K时由非晶态转变为晶态，在673 K时晶粒尺寸增大。在真空和空气中测量了Mo K边的边前峰强度。这些介孔二氧化钛负载Mo催化剂在新观察到的中间相，然后用于催化剂的乙醇-氧气反应。虽然在4.0wt%Mo/P-25催化剂上几乎只生成乙醛（这与文献中的结果一致），但在3.9wt%Mo/mesoTiO_2和4.0wt%Mo/mesoTiO_2上选择性地生成乙烯。

With the aid of dodecylamine as a mesostructure-directing agent, novel catalysts consisting of V, Ce, Mo and W supported on mesoporous titania were synthesized by the direct co-condensation of the alkoxides, X-meso TiO_2, or by the post-modification technique, X/meso TiO_2, where X=V, Ce, Mo and W. We investigated the phases of the support titania, the local structure of X as well as the ethanol-oxygen reaction on these catalysts. Calcination at 673 K induced a new mesophase in both catalysts, with a larger pore size (3.2-4.6 nm) than was originally presented (2.0-2.1 nm). This phase is not similar to any mesoporous titania ever reported previously. X-ray diffraction and Raman spectroscopy revealed that the phase transitions that occur at 573 K and 673 K in Mo/meso TiO_2 are from the amorphous to rutile and from the rutile to anatase phases, respectively. Changes from the rutile to the anatase phase with increasing temperature have rarely been observed before. In contrast, it was shown that Mo-meso TiO_2 is transformed from the amorphous to the anatase phase at 573 K, and that the size of the crystallites increased at 673 K. The intensity of pre-edge peak of the Mo K-edge was measured in vacuum and in air. These mesoporous titania-supported Mo catalysts in the newly-observed mesophase were then used to the catalyst for ethanol-oxygen reactions. Although acetaldehyde was almost exclusively formed on a 4.0 wt% Mo/P-25 catalyst (which agrees with the result in the literature) ethylene was selectively formed on 3.9 wt% Mo-meso TiO_2 and on 4.0 wt% Mo/meso TiO_2.