Interfacial catalytic degradation mechanism of n-hexane over polyhedral Co3O4 nanocatalysts derived from topotactic condensation of ZIF-67

Abstract

The development of efficient catalytic degradation of volatile organic compounds (VOCs) over nanostructured metal oxide catalysts with a polyhedral structure and anisotropic texture is in demand. Herein, a one-pot and scalable method is reported to synthesize polyhedral Co₃O₄ nanostructured-catalysts, which are involved in topotactic condensation of zeolitic imidazolate framework-67 (ZIF-67) through a pyrolysis-induced procedure. This condensation does not alter the topology of ZIF-67 precursors, thus it can be regarded as topotactic. The optimally prepared Co₃O₄-300 derived from ZIF-67 shows high catalytic performance for n-hexane oxidation with a T₉₀ of 196 °C at a gas hourly space velocity (GHSV) of 60 000 mL g⁻¹ h⁻¹, superior to commercial Pt/Al₂O₃. In addition, this catalyst also demonstrates satisfactory catalytic stability after five successive cycles of heating–cooling tests, excellent long-term durability after 90 h of on-stream reaction and strong resistance to water vapor and CO₂. Experimental results indicate that the topotactic polyhedral morphology, abundant acid sites and oxygen vacancies are beneficial for n-hexane oxidation. The interfacial catalytic degradation mechanism of n-hexane over Co₃O₄ nanocatalysts could be explained by a progressive transition from the Langmuir–Hinshelwood (L–H) model to Mars–van Krevelen (MvK) model. This work may provide a new strategy for rational design and synthesis of metal oxide nanocatalysts enabled by topotactic condensation of metal organic frameworks for catalytic degradation of typical VOCs in real environments.