Si-hydroxyls synergistically mediated small-sized CoOx nanoparticles in Si-beta zeolite for intensifying propane dehydrogenation
Cobalt (Co)-based zeolite catalysts are promising alternatives to replace expensive Pt- and toxic Cr-based catalysts for direct propane dehydrogenation (PDH). However, identifying the interaction between Co species and surface Si-hydroxyls of siliceous zeolites has been an inevitable challenge to realize the controllable construction of the Co species as dehydrogenation sites. Herein, we have fabricated a series of Co/Si-Beta(m-n) catalysts by using the dealuminated Si-Beta zeolites with “on-purpose” quantifying different type of Si-hydroxyls, involving geminal silanols ( g -SiOH), vicinal silanols ( v -SiOH) and silanol nests ( n -SiOH). In comparison to ultra-small CoO x nanoparticles (< 1.0 nm) directly trapped by the n -SiOH structure, a moderate interaction was built between tetrahedrally-coordinated divalent CoO x nanoparticles (∼4.5 nm) and external n -SiOH structure, resulting from partial migration and aggregation of initial CoO x species preferentially captured with g -/ v -SiOH structures during H 2 reduction. Given this, a representative Co/Si-Beta(500–12) catalyst exhibited a high catalyst productivity of 29.22 mol/g-catalyst (the product of initial reaction rate and the inverse of deactivation coefficient) with about 96 % propylene selectivity. In-situ FTIR spectra further revealed that such superior PDH performance was attributable to the moderately interaction of defined Si-O-Co structure that could be conducive to form the 2-propyl intermediate product, supporting the production of propylene and H 2 . These findings provide a novel inspiration for the development and optimization of low-cost, ecofriendly and advanced PDH catalysts.
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