Total oxidation of VOCs on mesoporous iron oxide catalysts: Soft chemistry route versus hard template method

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The total oxidation of two representative VOCs, propane and toluene, has been studied using mesoporous α-FeO catalysts. Different preparation methods have been followed leading to mesoporous materials with different characteristics. Whilst a mesoporous catalyst formed by aggregation of nanocrystals has been produced by soft chemistry using oxalic acid as precipitating agent, a mesoporous material with crystalline walls have been prepared by a nanocasting route using a hard template. These catalysts have been characterized by several physicochemical techniques: XRD, N adsorption, TPR, XPS, TEM, HR-TEM, SAED and EDX. Among the different α-FeO catalysts synthesized differences not only in the surface area and morphology have been observed but also in the lattice parameter, in the concentration of oxygen defects for VOCs adsorption and in the reducibility. In the case of the toluene oxidation it has been observed that the catalytic activity is highest for the catalysts prepared by a nanocasting route, which presents a very high surface area of 208 m g. Conversely, for propane oxidation the most active catalyst resulted to be the mesoporous nanocrystalline catalyst formed by aggregation. In this case, a direct relationship between reducibility and catalytic activity normalized per surface area has been observed. The differences between toluene and propane oxidation can be tentatively ascribed to different reaction mechanisms to be accounted for.
The authors would like to acknowledge the DGICYT in Spain (CTQ2012-37925-C03-1, CTQ2012-37925-C03-2, CTQ2012-37925-C03-3 and CTQ2012-37984-C02-01) and FEDER for financial support.