Iron Based Core-Shell Structures as Versatile Materials: Magnetic Support and Solid Catalyst

Transient Behavior of CO and CO2 Hydrogenation on Fe@SiO2 Core–Shell Model Catalysts—A Stoichiometric Analysis of Experimental Data

The hydrogenation of CO and CO2 from industrial exhaust gases into CH4 represents a promising method for sustainable chemical energy storage. While iron-based catalysts are in principle suitable for that purpose, the active metal Fe undergoes a complex transformation during the chemical reaction process. However, only little is known about the change in catalytically active species under reaction conditions, primarily caused by structural changes in the catalyst material, so far. By using core–shell model materials, factors that alter the catalyst structure can be excluded, making it possible to observe the direct influence of the reactants on the activity in the present work. Furthermore, stoichiometric analysis was used as a key tool for the evaluation of individual key reactions in the complex reaction network purely from experimental data, thus making it possible to draw conclusions about the catalyst state. In the case of CO hydrogenation, the presumed Boudouard reaction and the associated carburization of the catalyst can be quantified and the main reaction (CO methanation) can be determined. The results of the CO2 hydrogenation showed that the reverse water–gas shift reaction mainly took place, but under an ongoing change in the catalytic active iron phase. Due to the systematic exchange between CO and CO2 in the reactant gas stream, a mutual influence could also be observed. The results from the stoichiometric analysis provide the basis for the development of kinetic models for the key reactions in future work.

Synthesis of Hydroxyapatite/Iron Oxide Composite and Comparison of Selected Structural, Surface, and Electrochemical Properties

The paper presents the synthesis of a hydroxyapatite/iron oxide composite utilizing the wet chemical method, as well as the comparison of several selected material characteristics. As follows from the literature reports, hydroxyapatite is a common mineral possessing numerous significant properties. Nowadays, there is an increase in the amount of research on possible modifications of this compound. The promising way to improve hydroxyapatite features is its combination with iron oxide. Particularly, there can be two forms that are distinguished, namely Fe₃O₄ and γ-Fe₂O₃. These oxides exhibit valuable properties, particularly magnetism. A combination of the mentioned materials leads to multifunctional composite formation with many potential applications, as follows from several studies. However, this area of science is not fully developed. There are still many aspects to be examined. The synthesized composite and its components were analyzed by employing the following methods. The X-ray diffraction analysis revealed formation of hydroxyapatite and Fe₂O₃ crystalline phases. Moreover, porosimetry proved a larger specific area for the composite sample in comparison with other materials. The results obtained using the SEM method confirmed an external layer of hydroxyapatite and spherical shapes of internal Fe₂O₃ particles. Furthermore, the X-ray photoelectron spectroscopy data presented characteristic peaks of Fe, Ca, P, and O atoms in all samples. The Fourier Transform Infrared spectra displayed all the specific vibrations typical of the analyzed materials. What is more, the Vibrating Sample Magnetometer method confirmed the paramagnetic nature of the samples. It could be concluded that the synthesized composite has intermediate properties between the components used in the formation process. The results suggest that these composites are superparamagnetic. This type of material architecture would be well suited for biomedical applications.

Improved Solvothermal Synthesis of γ-Fe2O3 Magnetic Nanoparticles for SiO2 Coating

Monodisperse magnetic γ-Fe2O3 nanoparticles (MNPs) were prepared by a simple, improved, one-pot solvothermal synthesis using SDS and PEG 6000 as double capping reagents. This double protecting layer afforded better MNP uniformity (Z average 257 ± 11.12 nm, PDI = 0.18) and colloidal stability. Materials were characterized by DLS, SEM, TEM, XPS, and XRD. The use of these MNPs in the synthesis of core-shell structures with uniform and tunable silica coatings was demonstrated, as silica coated MNPs are important for use in a range of applications, including magnetic separation and catalysis and as platforms for templated nanogel synthesis.