Resolving Complex K-Pt-Sn Interactions in PtSn@K-MFI Catalysts for Alkane Dehydrogenation

Abstract

K and Sn contents were rationalized during the synthesis of PtSn@K-MFI to maximize metal dispersion and stability along the MFI crystallites. Experimental results and theoretical calculations reveal a stoichiometry of ∼1 K per unit cell of MFI, limiting then the final K incorporation within siliceous MFI crystals at ∼0.7 wt %. Above this stoichiometry, K is not incorporated into the final solids unless significant amounts of Sn are simultaneously present, leading to the formation of tin-silicate precipitates. The optimized PtSn@K-MFI catalysts improve the catalytic performance of well-established references, as PtSn/SiO2, for the propane dehydration (PDH) reaction. In particular, low Sn loadings (below 0.5 wt %) result in higher time-on-stream (TOS) deactivation catalytic profiles but excellent regenarability after consecutive PDH reaction, while higher Sn content (close to 1 wt %) minimizes TOS deactivation due to the maximization of Pt-Sn bonds but consecutive regenerations result in significant metal sintering. Increasing Sn contents within MFI crystallites facilitates Pt sintering and, thus, occurring catalyst deactivation upon regeneration cycles. As a result of complex interconnected nucleation/crystallization processes, fine-tuning rationalizations of one-pot synthesis approaches can substantially influence the final atomic and subnanometric metal interactions and, consequently, the catalytic and sintering-resistance properties when exposed to highly demanding industrial conditions.