Abstract:

1,2,3,4-tetrahydroquinoline derived from selective hydrogenation of quinoline has vital applications in the fields of pharmaceutical, alkaloid, agrochemical and so on, where tuning the interaction between quinoline molecules and active sites plays an important role in improving the catalytic performance. Herein, the effect of reduction temperature was explored with Rh/FePO₄ catalyst employed for the hydrogenation of quinoline. The results showed that the hydrogenation performance decreased along with increasing the reduction temperature, in which the catalyst reduced at 75℃ gave the best performance, yielding 98.5% conversion and >99% selectivity of 1,2,3,4-tetrahydroquinoline, as well as high reaction rate of 353mol/(mol·h). Various characterizations indicated that the catalyst structure changed from FePO₄ to amorphous crystal and Fe₂P₂O₇ phase at increased reduction temperature. Meanwhile, the high reduction temperature led to more metallic Rh species and the absent of acidic sites. Combining with the experimental results, we demonstrated that the decline in catalyst performance at high temperature is due to the formation of more metallic Rh species, which strongly coordinated with quinoline molecule and poisoned the active sites. And the catalyst reduced at a low temperature of 50℃ cannot form the metallic Rh species. Comparatively, the catalyst reduced at 75℃ had the suitable electronic property and acidic sites, both of which promoted the hydrogenation of quinoline under mild conditions.

Key words: catalyst, nanoparticles, hydrogenation, multiphase reaction, reactivity, selectivity

摘要：

喹啉选择加氢制1,2,3,4-四氢喹啉在医药、生物碱、农药等精细化学品领域具有重要应用，调变喹啉分子与催化活性中心的相互作用强度是提高加氢性能的关键。本文以Rh/FePO₄催化剂为研究对象，考察了氢气还原温度对喹啉催化加氢性能的影响。结果表明，随着还原温度升高，Rh/FePO₄催化剂加氢性能降低，其中，75℃还原催化剂表现出最优性能，喹啉转化率为98.5%，1,2,3,4-四氢喹啉选择性>99%，反应速率为353mol/(mol·h)。XPS、HAADF-STEM、NH₃-TPD、XRD等表征表明随着还原温度的提高，催化剂发生磷酸铁-无定型-焦磷酸亚铁的结构转变，同时，催化剂的酸性消失且金属Rh呈现更多金属态。结合实验结果，分析认为高温还原催化剂活性下降归因于过多金属态Rh物种的形成，与喹啉分子之间形成强的相互作用，毒化了催化剂的活性中心，而过低温度50℃还原不能形成金属态Rh物种。相比之下，75℃还原Rh/FePO₄催化剂具有合适的电子性质和酸性位点，二者之间的协同作用促进喹啉在温和条件下的选择加氢。

关键词: 催化剂, 纳米粒子, 加氢, 多相反应, 活性, 选择性