Fe的原位掺杂对Pt/Silicalite-1催化丙烷脱氢反应性能的提升作用

利用一步水热法制备了原位掺杂Fe的Silicalite-1分子筛载体，浸渍得到相应的Pt基催化剂，用于丙烷的直接脱氢反应。作为对比，也制备了Pt/Silicalite-1和共浸渍的Pt1Fe2/Silicalite-1催化剂。研究发现较之Pt/Silicalite-1催化剂，原位掺入Fe的Pt/Fe-Silicalite-1催化剂反应性能有了很大程度地提高，而共浸渍制备的Pt1Fe2/Silicalite-1催化剂反应性能有所降低。在Pt/Fe-Silicalite-1催化剂上，尽管丙烷的初始转化率略有降低，但丙烯的选择性和催化稳定性大幅提高。反应8 h后丙烷转化率稳定在43.7%、丙烯选择性达到98.0%；且在80 h内基本保持不变。深入表征发现Fe的原位掺入使得Pt物种配位饱和度提高，避免了丙烷的深度脱氢使得丙烯选择性提高、结焦速率降低；且通过Fe-Pt之间电子转移，使得Pt上的电子云密度增强，增强了丙烯的脱附能力，进一步降低了结焦速率。另外载体中的Fe位点可以锚定Pt，使得Pt物种不易聚集，从而进一步提高了Pt/Fe-Silicalite-1的稳定性，使得该催化剂在反应80 h后仍保持高转化率和选择性。

Performance Enhancement of Pt/Silicalite-1 by in situ Doped Fe for Propane Dehydrogenation

As one of the most common bulk chemicals, propylene is widely used in industrial production. Given developments in shale gas exploration technology, propane direct dehydrogenation (PDH) has emerged as a potential route. Pt-based catalysts are considered highly active catalysts for PDH, but their use is limited by a number of challenges. Herein, in situ Fe-doped Silicalite-1 zeolite supports were synthesized using the hydrothermal method, after which the corresponding Pt-based catalysts were prepared by impregnation and used for PDH. For comparison, Pt/Silicalite-1 and co-impregnated Pt1Fe2/Silicalite-1 catalysts were also prepared. Compared with that of Pt/Silicalite-1, the catalytic performance of Pt/Fe-Silicalite-1 prepared by in situ Fe-doping was significantly enhanced, whereas that of the co-precipitated Pt1Fe2/Silicalite-1 catalyst decreased. The selectivity and catalytic stability of the reaction over the Pt/Fe-Silicalite-1 catalyst were greatly improved, although the initial conversion of propane was slightly low. After 8 h, the propane conversion rate stabilized at 43.7% and the propylene selectivity reached 98.0%. More importantly, the catalyst maintained its performance over 80 h without an obvious decline. Propane conversion increased with increasing reaction temperature, while propene selectivity was maintained at a comparable level. The reaction kinetics of PDH were determined, and the results demonstrated that the apparent activation energy of the Pt/Fe-Silicalite-1 catalyst was 97.0 kJ?mol^?1; this value was the lowest obtained among the catalysts investigated and indicated the relative ease of propane activation over the catalyst. A series of characterization techniques, such as X-ray diffraction (XRD), N₂ sorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM), were used to explore the structural characteristics of the catalysts. The in situ Fe-doped Silicalite-1 zeolite supports retained their MFI structure but had a small particle size. UV-Vis spectroscopy revealed a large amount of Fe₂O₃ particles on the Pt1Fe2/Silicalite-1 surface; by contrast, Pt/Fe-Silicalite-1 possessed isolated tetrahedrally and octahedrally coordinated Fe³⁺ in the Fe-Silicalite-1 framework, as well as small oligomeric Fe species, such as Fe_xO_y, inside the zeolite pores. H₂-TPR revealed strong interactions between the Fe species and support in the Pt/Fe-Silicalite-1 catalyst. CO-DRIFT and X-ray photoelectron spectroscopy (XPS) indicated that the in situ incorporation of Fe not only improved the formation of Pt on the platform sites with high saturation, which prevented the deep-cracking of propane, but also enriched the electron cloud density on Pt by promoting electron transfer from Fe to Pt, thus enhancing the desorption of propylene and preventing coke formation. In addition, Fe sites in the support could anchor Pt to prevent their aggregation and improve the stability of Pt/Fe-Silicalite-1. Thus, high conversion and selectivity were obtained even after 80 h of reaction.