Iron-Doped Mesoporous Powders of Hydroxyapatite as Molybdenum-Impregnated Catalysts for Deep Oxidative Desulfurization of Model Fuel: Synthesis and Experimental and Theoretical Studies

Abstract

Mesoporous iron-doped hydroxyapatite (HA) powders with a surface area up to 141 m 2 /g were synthesized and characterized by a variety of analytical and computational approaches, including X-ray diffraction (XRD) and X-ray fluorescence spectroscopy (XRF), atomic emission spectrometry with inductively coupled plasma (AES-ICP), Fourier transform infrared absorption (FTIR), nitrogen adsorption−desorption (BET), scanning and transmission electron microscopy (SEM and TEM), electron paramagnetic resonance (EPR), and density functional theory (DFT). Based on the data of TEM with mapping, the homogeneous distribution of Fe was evidenced. Fe 3+ ions were detected by EPR, and according to DFT, Fe 3+ occupied the Ca(2) position. The second part of the manuscript was dedicated to evaluating the catalytic properties of the developed HA powders for oxidative desulfurization, which is a promising alternative to hydrotreating for fuel purification. For this purpose, the molybdenum was impregnated on the HA, and iron-HA powders and the influence of its amount and the iron content were investigated. The optimal process parameters such as rotation speed, amount of H 2 O 2 , reaction time, temperature, and quantity of the catalyst were established and for the first time, to the authors' best knowledge, complete conversion of dibenzothiophene in the presence of an HA-based catalyst was achieved due to a combination of active sites of iron cations and molybdate anions.

Radiation-Induced Stable Radicals in Calcium Phosphates: Results of Multifrequency EPR, EDNMR, ESEEM, and ENDOR Studies

“…One of the analytical, non-destructive tools for the investigation of CPs of both biogenic and synthetic origins is electron paramagnetic resonance (EPR) [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]. The increased sensitivity, spectral and temporal resolution, along with the improved stability of modern commercial EPR spectrometers has opened new possibilities in the study of CPs during the last decade, taking a step towards in situ EPR imaging (EPRI) [44].…”

Incorporation of Iron(II) and (III) in Hydroxyapatite—A Theoretical Study

“…The OHare located within the anion channel, surrounded by calcium ions, and do not largely influence the overall packing and the density of the cell. A similar scheme of charge compensation has been previously considered in Refs [27,28,45].…”

“…Accordingly, the synthesis and study of HAp-based catalytic systems with iron impurities have attracted great interest in recent years [21][22][23][24][25][26]. As reviewed by Goldberg et al [27,28], Fe-HAp and Fe oxide nanoparticles demonstrated high efficiency as a catalyst in the field of heavy oil purification via oxidative desulfurization and aquathermolysis methods, oil asphaltene extraction, etc. Besides catalytic applications, Fe-HAp nanoparticles are promising for cancer monitoring [29], as well as magnetic resonance imaging [30], targeted delivery of drugs, and for the treatment of cancer by a hyperthermic method [31].…”

“…The paramagnetic properties of HAp appear upon the addition of Fe 3+ ions, and with an increase in the concentration of iron ions, the magnetic susceptibility increases [37]. Goldberg et al [27,28] demonstrated that Fe 3+ introduction leads to an increase in surface area of nanohydroxyapatite particles, improving their catalytic properties for desulfurization of the model heavy oil.…”

Using DFT to Calculate the Parameters of the Crystal Field in Mn2+ Doped Hydroxyapatite Crystals

“…DFT calculations make it possible to determine the most probable substitution position for impurity ions and monitor changes in the unit cell geometry, changes in the local positions of surrounding ions caused by impurities, etc. [20][21][22][23][24][25]. In most cases, DFT calculations help to confirm the assumptions that are made on the basis of experimental data.…”