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Materials 2014, 7(6), 4243-4257; doi:10.3390/ma7064243
Article

Active Iron Sites of Disordered Mesoporous Silica Catalyst FeKIL-2 in the Oxidation of Volatile Organic Compounds (VOC)

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Received: 16 February 2014; in revised form: 21 May 2014 / Accepted: 23 May 2014 / Published: 30 May 2014
(This article belongs to the Special Issue Advances in Nanoporous Materials)
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Abstract: Iron-functionalized disordered mesoporous silica (FeKIL-2) is a promising, environmentally friendly, cost-effective and highly efficient catalyst for the elimination of volatile organic compounds (VOCs) from polluted air via catalytic oxidation. In this study, we investigated the type of catalytically active iron sites for different iron concentrations in FeKIL-2 catalysts using advanced characterization of the local environment of iron atoms by a combination of X-ray Absorption Spectroscopy Techniques (XANES, EXAFS) and Atomic-Resolution Scanning Transmission Electron Microscopy (AR STEM). We found that the molar ratio Fe/Si ≤ 0.01 leads to the formation of stable, mostly isolated Fe3+ sites in the silica matrix, while higher iron content Fe/Si > 0.01 leads to the formation of oligonuclear iron clusters. STEM imaging and EELS techniques confirmed the existence of these clusters. Their size ranges from one to a few nanometers, and they are unevenly distributed throughout the material. The size of the clusters was also found to be similar, regardless of the nominal concentration of iron (Fe/Si = 0.02 and Fe/Si = 0.05). From the results obtained from sample characterization and model catalytic tests, we established that the enhanced activity of FeKIL-2 with the optimal Fe/Si = 0.01 ratio can be attributed to: (1) the optimal concentration of stable isolated Fe3+ in the silica support; and (2) accelerated diffusion of the reactants in disordered mesoporous silica (FeKIL-2) when compared to ordered mesoporous silica materials (FeSBA-15, FeMCM-41).
Keywords: FeKIL-2; disordered mesoporous silica; interparticle mesoporosity; isolated iron; oligonuclear iron clusters; catalytic oxidation; VOC decomposition; XANES; EXAFS; AR-STEM FeKIL-2; disordered mesoporous silica; interparticle mesoporosity; isolated iron; oligonuclear iron clusters; catalytic oxidation; VOC decomposition; XANES; EXAFS; AR-STEM
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Rangus, M.; Mazaj, M.; Dražić, G.; Popova, M.; Tušar, N.N. Active Iron Sites of Disordered Mesoporous Silica Catalyst FeKIL-2 in the Oxidation of Volatile Organic Compounds (VOC). Materials 2014, 7, 4243-4257.

AMA Style

Rangus M, Mazaj M, Dražić G, Popova M, Tušar NN. Active Iron Sites of Disordered Mesoporous Silica Catalyst FeKIL-2 in the Oxidation of Volatile Organic Compounds (VOC). Materials. 2014; 7(6):4243-4257.

Chicago/Turabian Style

Rangus, Mojca; Mazaj, Matjaž; Dražić, Goran; Popova, Margarita; Tušar, Nataša N. 2014. "Active Iron Sites of Disordered Mesoporous Silica Catalyst FeKIL-2 in the Oxidation of Volatile Organic Compounds (VOC)." Materials 7, no. 6: 4243-4257.


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