Low Concentration Fe-Doped Alumina Catalysts Using Sol-Gel and Impregnation Methods: The Synthesis, Characterization and Catalytic Performance during the Combustion of Trichloroethylene

Carolina Maldonado,Jaime Valente,Aracely Hernández-Ramírez,Javier De La Rosa,Carlos Lucio-Ortiz,Felipe Barraza

doi:10.3390/ma7032062

Abstract

The role of iron in two modes of integration into alumina catalysts was studied at 0.39 wt% Fe and tested in trichloroethylene combustion. One modified alumina was synthesized using the sol-gel method with Fe added in situ during hydrolysis; another modification was performed using calcined alumina, prepared using the sol-gel method and impregnated with Fe. Several characterization techniques were used to study the level of Fe modification in the γ-Al2O3 phase formed and to correlate the catalytic properties during trichloroethylene (TCE) combustion. The introduction of Fe in situ during the sol-gel process influenced the crystallite size, and three iron species were generated, namely, magnetite, maghemite and hematite. The impregnated Fe-alumina formed hematite and maghemite, which were highly dispersed on the γ-Al2O3 surface. The X-ray photoelectron spectra (XPS), FT-IR and Mössbauer spectroscopy analyses revealed how Fe interacted with the γ-Al2O3 lattice in both catalysts. The impregnated Fe-catalyst showed the best catalytic performance compared to the catalyst that was Fe-doped in situ by the sol-gel method; both had better catalytic activity than pure alumina. This difference in activity was correlated with the accessibility of the reactants to the hematite iron species on the surface. The chlorine poisoning for all three catalysts was less than 1.8%.

Highlights

The catalytic activity of aluminas depends on their physicochemical properties, which can be controlled by the preparation method [1,2,3,4,5,6]
We previously reported the Langmuir-Hinshelwood (LH) mechanism of oxidation of TCE over zirconia doped with La and Fe [58], where molecular oxygen was considered to be dissociatively adsorbed onto an active site of the catalyst surface and adsorbed oxygen atoms reacted with a nearby hydrocarbon on the same type of active site
The role of iron in two different modes of integration was studied by incorporating Fe at a low concentration in situ during the sol-gel process or by impregnation of iron acetate solution into a pure alumina

Summary

Introduction

The catalytic activity of aluminas depends on their physicochemical properties, which can be controlled by the preparation method [1,2,3,4,5,6]. The sol-gel method provides an attractive, convenient route to manipulate the structural and textural properties and purity of a compound [7,8,9,10]. One of the main advantages of metal oxide materials obtained using the sol-gel method is that the properties can be altered by manipulating any of the processing steps during the formation of the precursors. This fact allows for the homogeneous mixing of transition metal cations at a molecular level and enhances the formation of polycrystalline particles with special properties.

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Conclusion