Oxidation of benzene to phenol with N2O over a hierarchical Fe/ ZSM-5 catalyst

Catalytic oxidation of benzene with N2O to phenol over the hierarchical and microporous Fe/ZSM-5-based catalysts in a continuous fixed bed reactor was investigated. The spent catalyst was in-situ regenerated by an oxidative treatment using N2O and in total 10 reaction -regeneration cycles were performed. A 100% N2O conversion, 93.3% phenol selectivity, and high initial phenol formation rate of 16.49 & PLUSMN; 0.06 mmolphenol gcatalyst -1 h-1 at time on stream (TOS) of 5 min, and a good phenol productivity of 147.06 mmolphenol gcatalyst-1 during catalyst lifetime of 1800 min were obtained on a fresh hierarchical Fe/ZSM-5-Hi2.8 catalyst. With the reaction-regeneration cycle, N2O conversion is fully recovered within TOS of 3 h, moreover, the phenol productivity was decreased ca. 2.2 & PLUSMN; 0.8% after each cycle, leading to a total phenol productivity of ca. 0.44 tonphenol kgcatalyst-1 estimated for 300 cycles. Catalyst characterizations imply that the coke is rapidly deposited on catalyst surface in the initial TOS of 3 h (0.28 mgc gcatalyst-1 min -1) and gradually becomes graphitic during the TOS of 30 h with a slow formation rate of 0.06 mgc gcatalyst -1 min -1. Among others (e.g., the decrease of textural property and acidity), the nearly complete coverage of the active Fe-O-Al sites by coke accounts for the main catalyst deactivation. Besides these reversible deactivation characteristics related to coking, the irreversible catalyst deactivation is also observed with the reaction-regeneration cycle. The latter is reflected by a further decreased amount of the active Fe-O-Al sites, which agglomerate on catalyst surface with the cycle, likely associated with the hard coke residue that is not completely removed by the regeneration.& COPY; 2022 Institute of Process Engineering, Chinese Academy of Sciences. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

The catalytic oxidation of benzene with N2O to phenol using a hierarchical and microporous Fe/ZSM-5-based catalyst was studied in a continuous fixed bed reactor. In-situ regeneration of the spent catalyst was achieved through oxidative treatment with N2O, and a total of 10 reaction-regeneration cycles were performed. The fresh hierarchical Fe/ZSM-5-Hi2.8 catalyst exhibited excellent performance with 100% N2O conversion, 93.3% phenol selectivity, and a high initial phenol formation rate. However, coke deposition on the catalyst surface led to reversible and irreversible deactivation, reducing the phenol productivity over time.