Uniformly stable hydroxylated cobalt(II) silicate species embedded within silicalite-1 zeolite for boosting propane dehydrogenation

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 Co 2+ 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 Co 2+ 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.