Abstract
Different Cu contents (x wt%) were supported on the cryptomelane-type manganese oxide octahedral molecular sieve (OMS-2) (xCu/OMS-2; x = 1, 5, 15, and 20) via a pre-incorporation method. Physicochemical properties of the OMS-2 and xCu/OMS-2 samples were characterized by means of the XRD, FT-IR, SEM, TG/DTG, ICP-OES, XPS, O2-TPD, H2-TPR, and in situ DRIFTS techniques, and their catalytic activities were measured for the oxidation of CO, ethyl acetate, and toluene. The results show that the Cu species were homogeneously dispersed in the tunnel and framework structure of OMS-2. Among all of the samples, 15Cu/OMS-2 sample exhibited the best activities with the T50% of 65, 165, and 240 °C as well as the T90% of 85, 215, and 290 °C for CO, ethyl acetate and toluene oxidation, respectively, which was due to the existence of the Cu species and Mn3+/Mn4+ redox couples, rich oxygen vacancies, good oxygen mobility, low-temperature reducibility, and strong interaction between the Cu species and the OMS-2 support. The reaction mechanisms were also deduced by analyzing the in situ DRIFTS spectra of the 15Cu/OMS-2 sample. The excellent oxygen mobility associated with the electron transfer between Cu species and Mn3+/Mn4+ redox couples might be conducive to the continuous replenishment of active oxygen species and the constantly generated reactant intermediates, thereby increasing the reactant reaction rate.
Highlights
Carbon monoxide (CO), ethyl acetate (CH3 COOC2 H5 ), and toluene (C6 H5 CH3 ) come from a variety of sources [1], and they give rise to severe pollution on atmospheric environment and are seriously harmful to human health
Taking the rich resource and relatively low cost as well as good catalytic activity into account, we envision that Cu/OMS-2 catalyst would possess a distinctive superiority in the catalytic removal of CO and volatile organic compounds (VOCs)
This might be caused by the replacement of the bigger K+ (138 pm in radium) by the smaller Cu species (54–77 pm in radium) in the tunnels of OMS-2 during the preparation process, in which Cu was connected to Mn through O to form a Cu–O–Mn bond
Summary
Carbon monoxide (CO), ethyl acetate (CH3 COOC2 H5 ), and toluene (C6 H5 CH3 ) come from a variety of sources (e.g., stationary industries, daily life, and vehicle exhaust emissions) [1], and they give rise to severe pollution on atmospheric environment and are seriously harmful to human health. The noble metal catalysts exhibit preferable activities towards removal of air pollutants; their resource scarcity, expensive cost, high-temperature agglomeration, and poisoning tendency limit their wide applications [5,6]. Transition metal oxides have good redox properties due to their unsaturated d orbitals [7]. Mn possesses various valence states (2+, 3+, 4+, and 7+), representing good redox property, whereas OMS-2 exhibits outstanding ion exchange performance. Taking the rich resource and relatively low cost as well as good catalytic activity into account, we envision that Cu/OMS-2 catalyst would possess a distinctive superiority in the catalytic removal of CO and volatile organic compounds (VOCs)
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