Migration-agglomeration-lockup of metal particles in zeolite for ultra-stable propane dehydrogenation catalysts

Abstract Propane dehydrogenation (PDH) over Pt catalyst operated in a moving-bed mode is becoming the dominant process for the on-purpose production of propylene worldwide1-3. Sintering and coking deactivations of Pt catalysts, which greatly decrease the durability and efficiency of this scarce and costly noble metal, are the most challenging issues for the sustainable development of the PDH process4. Even after over half a century of efforts, the development of long-term durable Pt catalysts that are feasible for more economic and efficient fixed-bed operation remains as a formidable task5-10. Herein we report a strategy to modulate the migration-agglomeration-lockup of Pt particles in zeolite silicalite-1 (S-1) for synthesizing highly sintering- and coking-resistant (Pt-Sn2)2@S-1 PDH catalysts. It is found that the migration of Pt-Sn2 clusters in S-1 crystals during the PDH reaction leads to a competition between intra-crystalline agglomeration and external-surface agglomeration of Pt-Sn2 clusters. We show that, when the b-axis length of S-1 crystals is longer than 2 μm, the intra-crystalline agglomeration becomes dominant over the external-surface agglomeration, resulting in the formation of ultra-stable (Pt-Sn2)2@S-1 in which the (Pt-Sn2)2 dimers are securely locked in the channels of S-1 crystals. The long-term durability (4500 hours or about 6 months on stream without perceptible deactivation tendency) of (Pt-Sn2)2@S-1 is at least three orders of magnitude higher than that of the best catalyst reported, which is expected to bring about a breakthrough in revolutionizing the moving-bed operation of the current PDH process to fixed-bed operation. We anticipate that modulating metal migration-agglomeration-lockup within zeolite can act as a general strategy for the synthesis of durable noble metal catalysts, which is beneficial to greatly maximizing the service lifetime of noble metals in industry application11-15.