B/W掺杂调控MoVTe酸性及异丁烯氧化产物选择性

Doping B/W to regulate the acidity of MoVTe and the selectivity of isobutylene oxidation

摘要:

为了有效调控异丁烯气相氧化产物（甲基丙烯醛或甲基丙烯酸）的选择性，以(NH4)6Mo7O24·4H2O、NH4VO3和H6TeO6为原料制备MoVTe，分别以H3BO3和(NH4)6H2W12O40·xH2O为原料使用蒸发浓缩法制备掺杂B、W的催化剂MoVTeB和MoVTeW，将其用于催化异丁烯（IB）气相氧化反应。采用XRD、XPS和NH3-TPD对MoVTeB和MoVTeW进行表征，考察B和W的掺杂量对MoVTeB和MoVTeW催化异丁烯气相氧化反应的性能的影响。结果表明，B和W的掺杂量分别为1.2和0.4（由B或W以mmol为单位的物质的量数值/2.4算得）的MoVTeB1.2和MoVTeW0.4表现出最佳的催化性能，在反应温度450 ℃，n(O2)∶n(IB)（氧烯比）为20∶2的最佳条件下，IB的转化率最高分别为90%和96%，甲基丙烯醛和甲基丙烯酸的选择性分别为80%和67%。在20 h的稳定性测试时间内，MoVTeB1.2和MoVTeW0.4均具有较好的催化稳定性。B掺杂减少了MoVTeB1.2强酸性位点，利于甲基丙烯醛的脱附和生成。W掺杂则增加了MoVTeW0.4强酸性位点，使甲基丙烯醛不能脱附，从而继续氧化生成甲基丙烯酸。

Abstract:

In order to effectively regulate the selectivity of isobutene gas-phase oxidation products (methacrolein or methacrylic acid), MoVTe mixed metal oxide catalysts were prepared using (NH?)?Mo?O??·4H?O, NH?VO? and H?TeO? as raw materials. B or W doped MoVTe mixed metal oxide catalysts (MoVTeB and MoVTeW) were then synthesized via evaporation concentration method, with H?BO? or (NH?)?H?W??O??·xH?O serving as B and W sources, respectively. These catalysts were applied in the catalytic gas-phase oxidation of isobutene (IB). XRD, XPS and NH?-TPD were employed to characterize MoVTeB and MoVTeW, focusing on the effects of B and W doping amounts on their catalytic performance in isobutene gas-phase oxidation. The results demonstrate that MoVTeB?.? and MoVTeW?.?, prepared with B and W doping amounts of 1.2 and 0.4 respectively (calculated by dividing the value of B/W amount in mmol by 2.4), exhibit optimal catalytic performance. Under the optimal reaction conditions of 450 ℃ and an oxygen-to-alkene ratio (n(O?)∶n(IB)) of 20:2, the maximum conversion rates of IB over these catalysts reach 90% and 96% respectively, with selectivities to methacrolein and methacrylic acid being 80% and 67% respectively. Both MoVTeB?.? and MoVTeW?.? show good catalytic stability during the 20-hour stability test. B doping reduces the number of strong acidic sites in MoVTeB?.?, which is beneficial for the desorption and formation of methacrolein. In contrast, W doping increases the strong acidic sites in MoVTeW?.?, making methacrolein unlikely to desorb and thus promoting its further oxidation to methacrylic acid.