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Co-based catalysts are promising alternatives to replace expensive Pt- and toxic Cr-based catalysts for propane dehydrogenation (PDH), while the catalytic stability and propylene selectivity have been subjected to the diversity of Co speciations. Given the situation, uniformly stable hydroxylated Co2+ silicate sites (depicted as {OH–Si–(OH)–Co–O–Si-(OH) 3 }) are successfully embedded into the silicalite-1 zeolite framework located in the straight and intersection channels (Co@S-1) with the assistance of Co precursors and geminal silanols via a facile hydrothermal synthesis, as revealed by detail characterizations. Under comparable conditions, a superior catalytic PDH performance with attractive propylene formation rate of 14.6 mmol·g cat −1·h−1, propylene selectivity higher than 93% and very low deactivation rate of 0.0206 h−1 after 7 h is achieved over the Co@S-1(EDA) catalyst. Furthermore, the catalytic performance can be restored to the same as that of the fresh catalyst after 3 successive regenerations. In situ FTIR spectra analysis further reveals the dynamic changes in the characteristic absorption bands associated with the hydroxylated Co2+ silicate sites and the intermediate product (2-propyl) during the PDH reaction and a reaction mechanism is proposed accordingly. This work provides a new insight for designing high-efficiency nonprecious metal PDH catalysts. [Display omitted] • Coordination environments of Co precursor complexes were precisely modulated. • Hydroxylated Co2+ silicate sites were fabricated with the assistance of Co precursors and geminal silanols. • Co@S-1(EDA) catalyst exhibited superior catalytic performance in PDH reaction. • A possible reaction mechanism was proposed from in situ FTIR spectra. [ABSTRACT FROM AUTHOR]

A highly stable bimetallic-sites catalyst of Ni-Zn anchored in the silicalite-1 zeolite framework is facilely fabricated by ligand-protected strategy, synergistically boosting propane dehydrogenation to propylene. [Display omitted] • Bimetallic Ni-Zn site anchored in the silicalite-1 zeolitic framework are fabricated. • Superior catalytic performance on the 0.2Ni0.06Zn-S-1 for PDH is achieved. • High stability and activity of catalyst are remained after regeneration for 4 cycles. • Synergistic effect between Ni-Zn sites favors propylene desorption to reduce coke deposition. Propane dehydrogenation (PDH) is a prospective benign process for the production of propylene, but generally depends on high-price Pt and toxic Cr(VI) catalysts that often suffer from the rapid deactivation derived from metal sintering and severe coke deposition. To overcome these problems, the breakthroughs in an alternative catalyst design with efficient, low-cost and eco-friendly play a crucial role in successfully developing this process. Here, we facilely fabricate the bimetallic-site catalyst of Ni-Zn anchored in the zeolitic framework of silicalite-1 (depicted as NiZn-S-1) by employing ligand-protected strategy, which performs high temperature stability. Under comparable conditions, the NiZn-S-1 catalyst with high Ni/Zn molar ratio of 3:1 (named 0.2Ni0.06Zn-S-1) exhibits superior catalytic activity (initial propane conversion of 32.5 % and actual TOF propane of 28.5 min−1) with low deactivation rate (0.0778 h−1) and great propylene selectivity (>90%) after 30 h on stream. In particular, the catalytic performance on this catalyst almost keeps same as that of fresh catalyst after 4 successive oxidation–reduction cycles. Multiple characterizations further demonstrate that the enhancement of PDH performance ought to be attributed to the synergistic effect between bimetallic Ni-Zn sites, which favors the selective activation of C–H bond and propylene desorption to reduce the formation of coke species with high graphitization degree, boosting the improvement of catalyst stability. The design of novel bimetallic-sites catalyst can give a new idea on the development of alternative PDH catalysts with economical- and environment-friendly in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • Si-hydroxyl variations for the Si-Beta zeolites before/after loading Co species were quantified. • A moderate interaction between small-sized CoO x nanoparticles and n -SiOH was achieved. • Co/Si-Beta(500–12) zeolite enabled enviable catalyst productivity and propylene selectivity. • The relationship between catalyst productivity and Si-hydroxyls variation was illustrated. • Propane dehydrogenation mechanism was revealed by in-situ FTIR spectroscopy. 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. [ABSTRACT FROM AUTHOR]