Gas-Phase Total Oxidation of Benzene, Toluene, Ethylbenzene, and Xylenes Using Shape-Selective Manganese Oxide and Copper Manganese Oxide Catalysts

Volatile organic compounds (VOCs) continue to be the major source of direct and indirect air pollution. Here, cryptomelane-type octahedral molecular sieve (OMS-2) manganese oxide, amorphous manganese oxide (AMO), and mixed copper manganese oxide (CuO/Mn2O3) nanomaterials were synthesized and, togeth...

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Bibliographic Details
Published in:	Journal of physical chemistry. C Vol. 116; no. 22; pp. 12066 - 12078
Main Authors:	Genuino, Homer C, Dharmarathna, Saminda, Njagi, Eric C, Mei, Michael C, Suib, Steven L
Format:	Journal Article
Language:	English
Published:	Columbus, OH American Chemical Society 07-06-2012
Subjects:	Catalysis Catalysts: preparations and properties Chemistry Condensed matter: structure, mechanical and thermal properties Cross-disciplinary physics: materials science; rheology Exact sciences and technology General and physical chemistry Materials science Nanoscale materials and structures: fabrication and characterization Other topics in nanoscale materials and structures Physics Solid surfaces and solid-solid interfaces Structure and morphology; thickness Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties) Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry Thin film structure and morphology Toluene Volatile organic compound Selectivity Molecular sieve Structure factor Manganese oxides Adsorption Strong correlation Benzene Morphology Oxidation Gas phase Microstructure Copper oxide Catalyst activity Nanostructured materials Catalyst
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Summary:	Volatile organic compounds (VOCs) continue to be the major source of direct and indirect air pollution. Here, cryptomelane-type octahedral molecular sieve (OMS-2) manganese oxide, amorphous manganese oxide (AMO), and mixed copper manganese oxide (CuO/Mn2O3) nanomaterials were synthesized and, together with commercial MnO2, characterized by various techniques. These catalysts were investigated for gas-phase total oxidation of six VOCs under air atmosphere. Using OMS-2 at 250 °C, the average conversions for toluene, benzene, ethylbenzene, p-xylene, m-xylene, and o-xylene were 75%, 61%, 45%, 23%, 13%, and 8%, respectively, whereas using CuO/Mn2O3, 72%, 44%, 37%, 29%, 27%, and 26%, respectively, were obtained. Generally, the conversion of VOCs to CO2 using the synthesized catalysts increased in the order: o-xylene ≈ m-xylene < p-xylene < ethylbenzene < benzene < toluene. However, using commercial MnO2, benzene (44% conversion) was more reactive than toluene (37%), and the xylenes showed similar reactivities (13–20%). Differences in reactivity among VOCs were rationalized in terms of degree of substrate adsorption and structural effects. For example, the reactivity of xylenes was dictated by the shape-selectivity of stable OMS-2. The higher oxidative activities exhibited by OMS-2, AMO, and CuO/Mn2O3 as compared to commercial MnO2 were attributed to a combination of factors including structure, morphology, hydrophobicity, and redox properties. The mobility and reactivity of active oxygen species were strongly correlated with catalytic activities. Lattice oxygen was involved in the VOC oxidation, suggesting that the reaction could proceed via the Mars–van Krevelen mechanism.
ISSN:	1932-7447 1932-7455
DOI:	10.1021/jp301342f