Controlled synthesis of diverse manganese oxide-based catalysts for complete oxidation of toluene and carbon monoxide

• Reacting fresh manganese hydroxide and acetic acid produces nanosized MnOx.
• The HAc/Mn ratio controls over morphology and crystal phase of produced MnOx.
• Specific surface area of catalyst is crucial in oxidation of carbon monoxide.
• Redox properties of catalyst play dominant roles in oxidation of toluene.

Manganese oxides with various morphologies and crystal structures for catalytic oxidation of air pollutants were synthesized by reacting fresh manganese hydroxide and acetic acid (HAc) at an HAc/Mn molar ratio of 1, 2 or 3. The characterizations and activity tests indicates that the HAc/Mn ratio has significant influence on the properties and the catalytic activities of the produced manganese oxides. Manganese oxide produced at an HAc/Mn ratio of 2 is composed of nanorods having relatively uniform diameters, and it possesses the most reducible manganese oxide species and the highest content of surface adsorbed oxygen species, which could contribute to its best activity in the catalytic deep oxidation of toluene. Manganese oxide produced at an HAc/Mn ratio of 3 possesses the largest specific surface area and is the most efficient in the catalytic oxidation of carbon monoxide. Palladium was impregnated onto manganese oxide at a loading of 0.3 wt% to investigate their combined effects on catalytic destruction of the pollutants. The incorporation of palladium causes decreased activity in catalytic oxidation of toluene, which might be associated with the reduction in the amount of active surface oxygen species on the catalyst. In contrast, palladium actually promotes the catalytic oxidation of carbon monoxide probably due to the additional adsorption of carbon monoxide on noble metal.

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