• Accepted manuscript •

### Performance Enhancement of Pt/Silicalite-1 by In Situ Doped Fe for Propane Dehydrogenation

Shanshan Shen, Xiaohui Liu, Yong Guo, Yanqin Wang

1. Research Institute of Industrial Catalysis, School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai 200237, China
• Received:2022-09-29 Revised:2022-11-21 Accepted:2022-11-21 Published:2022-11-24
• Contact: Yanqin Wang E-mail:wangyanqin@ecust.edu.cn
• Supported by:
This work was supported by the National Natural Science Foundation of China (21832002).

Abstract: 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 FexOy, 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.

MSC2000:

• O643