分子筛稳定的Lewis酸稀土中心在醛自缩合反应中的应用

羟醛缩合是重要的C–C键偶联反应,可以增长碳链,降低O/C比,用于生产很多大宗化学品,在生物质转化和生物油升级中广受关注.本文以丙醛分子自缩合反应作为模型反应,对比研究了稀土分子筛和稀土氧化物在醛自缩合反应中的催化性能,发现稀土分子筛的活性远高于稀土氧化物,其中Y/Beta活性最佳,并且具有良好的循环性能.随后采用程序...

Self-aldol condensation of aldehydes over Lewis acidic rare-earth cations stabilized by zeolites

The self-aldol condensation of aldehydes was investigated with rare-earth cations stabilized by [Si]Beta zeolites in parallel with bulk rare-earth metal oxides. Good catalytic performance was achieved with all Lewis acidic rare-earth cations stabilized by zeolites and yttrium appeared to be the best metal choice. According to the results of several complementary techniques, i.e., tempera-ture-programmed surface reactions, in situ diffuse reflectance infrared Fourier transform spectros-copy, ultraviolet-visible diffuse reflectance spectroscopy, the reaction pathway and mechanism of the aldehyde self-aldol condensation over Y/Beta catalyst were studied in more detail. Density func-tional theory calculations revealed that aldol dehydration was the rate-limiting step. The hydroxyl group at the open yttrium site played an important role in stabilizing the transition state of the aldol dimer reducing the energy barrier for its hydration. Lewis acidic Y(OSi)(OH)2 stabilized by zeolites in open configurations were identified as the preferred active sites for the self-aldol condensation of aldehydes.