Preparation, Characterization, and Application of Magnetic Fe-SBA-15 Mesoporous Silica Molecular Sieves

Magnetic Fe-SBA-15 mesoporous silica molecular sieves were prepared, characterized, and used for magnetic separation. Wet impregnation, drying, and calcination steps led to iron inclusion within the mesopores. Iron oxide was reduced to the metal form with hydrogen, and the magnetic Fe-SBA-15 was obtained. Fourier-transform infrared spectroscopy confirmed the preparation process from the oxide to metal forms. The structure of magnetic materials was confirmed by Mössbauer spectra. Powder X-ray diffraction data indicated that the structure of Fe-SBA-15 retained the host SBA-15 structure. Brunauer-Emmett-Teller analysis revealed a decrease in surface area and pore size, indicating Fe-SBA-15 coating on the inner surfaces. Scanning electron micrographs confirmed the decrease in size for modified SBA-15 particles. From scanning electron micrographs, it was found that the size of the modified SBA-15 particles decreased. Transmission electron micrographs also confirmed that modified SBA-15 retained the structure of the parent SBA-15 silica. Fe-SBA-15 exhibited strong magnetic properties, with a magnetization value of 8.8 emu g−1. The iron content in Fe-SBA-15 was determined by atom adsorption spectroscopy. Fe-SBA-15 was successfully used for the magnetic separation of three aromatic compounds in water. Our results suggest wide applicability of Fe-SBA-15 magnetic materials for the rapid and efficient separation of various compounds

Chemical Looping Technology for Energy Storage and Carbon Emissions Reductions

Chemical looping (CL) technology, initially developed as an advanced combustion method, has been widely applied in various processes, including the selective oxidation of hydrocarbons (e [...

Effect of magnesium substitution into Fe-based La-hexaaluminates on the activity for CH4 catalytic combustion

With the introduction of Mg2+ into Fe-substituted La-hexaaluminate precursors, a series of monophasic LaMgxFeAl11-xO19 (x = 0, 0.3, 0.7, 1) catalysts were prepared and tested as catalysts for CH4 catalytic combustion. The results show that the introduction of an appropriate amount of Mg2+ (x = 0.7) could significantly enhance the catalytic activity of Fe-substituted La-hexaaluminates and promote the resistance to deactivation after calcination at 1300 degrees C. The beneficial effect of Mg2+ is attributed to the fact that the presence of Mg2+ not only increased the distribution of Fe3+ in the mirror planes of La-hexaaluminates but also effectively suppressed the generation of catalytically inactive Fe2+. Besides, the LaMg0.7FeAl10.3O19 catalyst exhibits excellent stability for 100 h at 700 degrees C under the reaction conditions

Sn promoted BaFeO3-delta catalysts for N2O decomposition: Optimization of CrossMark Fe active centers

A series of BaFe1-xSnxO3-delta catalysts were prepared by sol-gel method and tested for N2O decomposition to shed light on the effect of B-site substitution on the catalytic behavior of perovskite catalysts. Sn-119 and Fe-57 Mossbauer results confirmed that the 5-fold coordinated Fe3+ cations with one adjacent oxygen vacancy (Fe3+-O-5) were the main active centers for N2O decomposition. Doping of Sn cations can significantly improve the percentage of Fe3+-O-5 from 30% (x = 0) to 68% (x = 0.8). More importantly, the valence state of Fe could be gradually reduced due to weakening of Fe-O bond with increasing the Sn content, which was attributed to the stronger force of Sn than Fe in Fe-O Sn structure to draw the oxygen anion and expansion of unit cell volume. Such change of Fe chemical state favored the oxygen mobility of the catalyst, leading to reduction in activation energy for N2O decomposition from ca. 241 (x = 0) to 178 kJ moL(-1) (x = 0.8). BaFe0.2Sn0.8O3-delta,5 catalyst exhibited the highest intrinsic rate of 1.49 s(-1) (550 degrees C), nearly 4 times larger than that of BaFeO3-delta (0.43 s(-1)). (C) 2017 Elsevier Inc. All rights reserved

A molten carbonate shell modified perovskite redox catalyst for anaerobic oxidative dehydrogenation of ethane

Acceptor-doped, redox-active perovskite oxides such as La0.8Sr0.2FeO3 (LSF) are active for ethane oxidation to CO X but show poor selectivity to ethylene. This article reports molten Li2CO3 as an effective "promoter" to modify LSF for chemical looping-oxidative dehydrogenation (CL-ODH) of ethane. Under the working state, the redox catalyst is composed of a molten Li2CO3 layer covering the solid LSF substrate. The molten layer facilitates the transport of active peroxide (O-2(2-)) species formed on LSF while blocking the nonselective sites. Spectroscopy measurements and density functional theory calculations indicate that Fe4+ -> Fe3+ transition is responsible for the peroxide formation, which results in both exothermic ODH and air reoxidation steps. With >90% ethylene selectivity, up to 59% ethylene yield, and favorable heat of reactions, the core-shell redox catalyst has an excellent potential to be effective for intensified ethane conversion. The mechanistic findings also provide a generalized approach for designing CL-ODH redox catalysts

Preparation of BaSnO3 and Ba(0.9)6La(0.04)SnO(3) by reactive core-shell precursor: formation process, CO sensitivity, electronic and optical properties analysis

We propose a facile and economic strategy for preparing BaSnO3 particles from a room-temperature fabricated BaCO3@SnO2 core-shell precursor. The core-shell structure promoted the mixing degree of the reactants and effectively suppressed sintering of the particles, therefore, pure BaSnO3 was obtained at 800 degrees C, nearly 400 degrees C lower than traditional solid-state reaction (SSR) method, and showed better CO sensitivity than BaSnO3 prepared by SSR route. The phase transformation, morphology changes, and structure evolution from the precursor to the final BaSnO3 were systematically investigated, and a clear picture of the formation mechanism of BaSnO3 was given. Slightly La doped BaSnO3 was prepared through the same procedure as BaSnO3, which proved the availability of this method for synthesis of slightly doped BaSnO3 materials. The optical properties and total conductivity of pure and La doped BaSnO3 were compared. The results showed that the band gap of the La-doped sample was slightly increased, while the resistivity was more than six orders of magnitude lower than that of pure BaSnO3. The underlying reason was studied for the first time by directly monitoring the electron structure of Sn cations at the atomic scale using Sn-119 Mossbauer spectroscopy. It was found that the introduction of La in BaSnO3 solid solution would induce electron donating to the 5s orbital of Sn4+, and Sn cations were slightly reduced. This result gave clear evidence of conduction band filling in La-doped BaSnO3, which accounted for the change in the electric and optical properties

A Facile Peroxo-Precursor Synthesis Method and Structure Evolution of Large Specific Surface Area Mesoporous BaSnO₃

In this paper, we propose a facile and efficient strategy for synthesizing mesoporous BaSnO₃ with a surface area as large as 67 m²/g using a peroxo-precursor decomposition procedure. As far as we know, this is the largest surface area reported in literature for BaSnO₃ materials and may have a potential to greatly promote the technological applications of this kind of functional material in the area of chemical sensors, NO_<i>x</i> storage, and dye-sensitized solar cells. The structure evolution of the mesoporous BaSnO₃ from the precursor was followed using a series of techniques. Infrared analysis indicates large amount of protons and peroxo ligands are contained in the peroxo-precursor. Although the crystal structure of the precursor appears cubic according to the analysis of X-ray diffraction data, Raman and Mössbauer spectroscopy results show that the Sn atom is offset from the center of [SnO₆] octahedron. After calcination at different temperatures, the precursor gradually transforms into BaSnO₃ by release of water and oxygen, and the distortion degree of [SnO₆] octahedral decreases. However, a number of oxygen vacancies are generated in the calcined samples, which are further confirmed by the physical property measurement system, and they would lower the local symmetry to some content. The concentration of the oxygen vacancies reduces simultaneously as the calcination temperature increases, and their contributions to the total heat capacity of the sample are calculated based on theoretical analysis of heat capacity data in the temperature region below 10 K

Breaking the stoichiometric limit in oxygen-carrying capacity of Fe-based oxygen carriers for chemical looping combustion using the Mg-Fe-O solid solution system

The performance of oxygen carriers contributes significantly to the efficiency of chemical looping combustion (CLC), an emerging carbon capture technology. Despite their low cost, Fe2O3-based oxygen carriers suffer from sintering-induced deactivation and low oxygen-carrying capacity (OCC) during CLC operations. Here, we report the development of a sintering-resistant MgO-doped Fe2O3oxygen carrier with an optimal composition of 5MgO·MgFe2O4, which exhibits superior cyclic stability and an OCC of 0.45 mol O/mol Fe (2.25 mmol O/gsolid), exceeding the widely accepted OCC limit of 0.167 mol O/mol Fe (2.08 mmol O/gsolid) of unmodified commercial Fe2O3. This result distinguishes this report from all past studies, in which efforts to enhance the cyclic stability of Fe-based oxygen carriers would always result in dilution of the OCC. The capacity enhancement by MgO is attributed to the unique mixtures of MgxFe1-xO (halite) and Mg1-yFe2+yO4(spinel) solid solutions, which effectively reduce the exergonicity for the reduction from Fe3+to Fe2+, while preventing any irreversible structural transformations during the redox process. This hypothesis-driven oxygen carrier design approach provides a new avenue for tailoring the lattice oxygen activities of oxygen carriers for chemical looping applications.Ministry of Education (MOE)National Research Foundation (NRF)Submitted/Accepted versionThe authors acknowledge financial support by the Ministry of Education Singapore’s Academic Research Fund Tier 1 (RT03/19 and RG112/18) and the National Research Foundation (NRF), Prime Minister’s Office, Singapore, under its Campus for Research Excellence and Technological Enterprise (CREATE) programme. Y.D. is grateful for financial support from the National Natural Science Foundation of China (21802070)

Synergy of the catalytic activation on Ni and the CeO2-TiO2/Ce2Ti2O7 stoichiometric redox cycle for dramatically enhanced solar fuel production

Solar thermochemical approaches to CO2 and H2O splitting have emerged as an attractive pathway to solar fuel production. However, efficiently producing solar fuel with high redox kinetics and yields at lower temperature remains a major challenge. In this study, Ni promoted ceria-titanium oxide (CeO2-TiO2) redox catalysts were developed for highly effective thermochemical CO2 and H2O splitting as well as partial oxidation of CH4 at 900 degrees C. Unprecedented CO and H-2 production rates and productivities of about 10-140 and 5-50 times higher than the current state-of-the-art solar thermochemical carbon dioxide splitting and water splitting processes were achieved with simultaneous close to complete CH4 conversions and high selectivities towards syngas. The underlying mechanism for the exceptional reaction performance was investigated by combined experimental characterization and density functional theory (DFT) calculations. It is revealed that the metallic Ni and the Ni/oxide interface manifest catalytic activity for both CH4 activation and CO2 or H2O dissociation, whereas CeO2-TiO2 enhances the lattice oxygen transport via the CeO2-TiO2/Ce2Ti2O7 stoichiometric redox cycle for CH4 partial oxidation and the subsequent CO2 or H2O splitting promoted by catalytically active Ni. Such findings substantiate the significance of the synergy between the reactant activation by catalytic sites and the stoichiometric redox chemistry governing oxygen ion transport, paving the way for designing prospective materials for sustainable solar fuel production