【摘要】 在原位条件下利用漫反射红外技术对丙烯选择氨氧化反应进行了研究。结果表明:(1)丙烯氨氧化反应的速率控制步骤是丙烯脱除α-H生成烯丙基中间物种,其吸收峰在1487cm-1;(2)催化剂表面上氨中间物种存在四种结合方式:(i)氨解离形成NH2中间物种(1553cm-1);(ii)Bronsted酸性位上形成NH4+中间物种(1659cm-1和1443cm-1);(iii)Lewis酸性位上形成配位氨中间物种(1257cm-1),它是由丙烯醛生成丙烯腈所需的氨物种;(iv)通过估算法初步确认催化剂表面上存在Mo=NH中间物种(1029cm-1),它是由丙烯直接生成丙烯腈所需的氨物种;(3)丙烯腈生成路线有两条:一是丙烯在钼亚氨物种作用下直接生成丙烯腈,反应机理模型为Grasselli模型;二是丙烯选择氧化生成的中间产物丙烯醛在配位氨物种作用下通过加成反应生成丙烯腈。以上结果不仅完善了丙烯氨氧化反应机理,而且对丙烯醛在反应过程中作用的认识更进了一步。更多还原

【Abstract】 Based on the in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), the intermediates and mechanisms of propylene ammoxidation were deeply investigated. The DRIFT spectra show that the formation of surface allylic species (1487 cm-1), which is derived from α-hydrogen abstraction of propylene, is the rate controlling step of the propylene ammoxidation. Through the study of the DRIFT spectra, the existence of four kinds of ammonia intermediate species on the catalyst surface can be found as follows: (ⅰ) the dissociation of the ammonia chemisorbed on the catalyst surface can take place with the formation of NH2 species (1553 cm-1); (ⅱ) complete proton transfer can occur with the formation of NH4+ ion (1659 cm-1 and 1443 cm-1) on Brφ nsted acid sites; (ⅲ) ammonia coordination intermediate (1257 cm-1) forms on Lewis acid sites, which plays a crucial role in the formation of acrylonitrile from acrolein via partial oxidation of propylene; (ⅳ) molybedenum-imido species (Mo=NH) (1029 cm-1) on catalyst surface is preliminary confirmed as the intermediate formed during the formation of acrylonitrile from the direct ammoxidation of propylene. It was found that there are two synthetic routes for the synthesis of acrylonitrile: the one is the direct ammoxidation of propylene, the mechanism of which is based on the Grasselli model; and the other is the addition reaction of the ammonia coordinated intermediate with acrolein produced via propylene selective oxidation. The above results not only make the mechanisms of propylene ammoxidation clear, but also improve the recognition of the role played by acrolein in the propylene ammoxidation.更多还原