Tin-Exchanged Siliceous Supports for Propane Dehydrogenation

Simultaneous increase in shale gas production and rise in olefin demand necessitate active and selective catalysts for light alkane dehydrogenation. Tin dispersed on siliceous supports is a promising alternative to current industrial catalysts, most notably with regard to increased stability and high propylene selectivity. Recently, tin supported on silica and on dealuminated BEA have shown considerable activity for propane dehydrogenation, but detailed kinetics and characterization are lacking. We strive to fill this knowledge gap by preparing, characterizing, and preforming catalytic testing on tin-exchanged dealuminated BEA (deAlBEA) and silica (SiO₂). Sn/deAlBEA and Sn/SiO₂ were prepared using a wetness impregnation procedure. These catalysts were characterized with Fourier transform infrared spectroscopy (FTIR), pyridine and acetonitrile FTIR, x-ray diffraction (XRD), UV-vis spectroscopy, and elemental analysis, and their activity for propane dehydrogenation was evaluated. FTIR confirms the exchange of Sn with silanol nests in deAlBEA and the creation of Lewis acid sites upon Sn introduction. UV vis spectroscopy and XRD confirm the lack of bulk SnO₂ particles, and elemental analysis with ICP-OES confirms metal weight loadings. Sn-deAlBEA catalysts exhibited high selectivity (up to 98%) to propylene, while residual silanol groups resulted in lower propylene selectivity for Sn/SiO₂ catalysts. The activity and stability of these catalysts were largely dependent on preparation method rather than metal weight loading. Increasing tin content resulted in increased propane dehydrogenation activity. Dehydrogenation and cracking rates and activation energies for these processes are also compared across tin catalysts. These Sn catalysts can also serve as promising supports for isolated Pt sites for propane dehydrogenation, which will be investigated in the future.