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用XRD、LRS、ESR、XPS等方法对机械混合物焙烧法制备的两组MoO_3—TiO_2催化剂进行了表征,同时考察了催化剂的甲醇选择氧化活性和选择性。结果表明:MoO_3与TiO_2机械混合物在450℃焙烧过程中发生TiO_2中锐钛矿转变成金红石的相变,但若将TiO_2在空气中550℃预处理8h后再与MoO_3混合焙烧则未观察到相变的发生。在上述两组催化剂中都发生了MoO_3在TiO_2表面的分散。当MoO_3含量小于10wt％时,MoO_3晶相消失,钼以表面钼氧物种存在。MoO_3与TiO_2之间的强相互作用导致Mo(Ⅴ)的生成和pKa≤+3.3的表面酸位的产生。TiO_2晶型对催化剂表面结构及反应活性有明显影响,锐钛矿转变为金红石使最佳反应温度提高20～40℃,Mo在表面富集程度增大,而Mo(Ⅴ)和表面酸位浓度下降。表面Mo(Ⅴ)和高分散于表面的八面体配位钼氧物种可能是甲醇氧化的活性位。
Two groups of MoO 3 -TiO 2 catalysts prepared by roasting with mechanical mixture were characterized by XRD, LRS, ESR and XPS. Meanwhile, the selectivity and catalytic activity of the catalyst for methanol oxidation were investigated. The results show that the phase transition from anatase to rutile occurs in the mechanical mixture of MoO_3 and TiO_2 during the calcination at 450 ℃. However, if the TiO_2 is pretreated at 550 ℃ in air for 8h and then mixed with MoO_3, it is not observed The occurrence of phase change. In the above two groups of catalysts, the dispersion of MoO 3 on the surface of TiO 2 occurred. When the content of MoO_3 is less than 10wt%, the crystal phase of MoO_3 disappears and the molybdenum exists as surface molybdenum oxygen species. The strong interaction between MoO_3 and TiO_2 leads to the formation of Mo (Ⅴ) and the generation of surface acid sites with pKa≤ + 3.3. The crystal structure of TiO 2 and the reactivity of the catalyst have obvious effects. The anatase to rutile increases the optimum reaction temperature by 20-40 ℃, and the enrichment of Mo on the surface increases. However, the concentration of Mo (Ⅴ) decline. The surface Mo (Ⅴ) and octahedral coordination molybdenum oxygen species highly dispersed on the surface may be the active sites for methanol oxidation.