Promotion effect of additive Fe on Al2O3 supported Ni catalyst for CO2 methanation

In this paper, the effect of additive Fe on Ni/Al₂O₃ catalyst for CO₂ methanation was studied. A series of bimetallic Ni–Fe catalysts with different Ni/Fe ratios were prepared by impregnation method. For comparison, monometallic Fe‐based and Ni‐based catalysts were also prepared by the same method. The characterization results showed that adding Fe to Ni catalyst on the premise of a low Ni loading(≦12 wt.%) enhanced CO₂ methanation performance. However, when the Ni loading reached 12 wt.%, the catalytic activity decreased with the increase of Fe content, but still higher than the corresponding Ni‐based catalyst without Fe. Among them, the 12Ni3Fe catalyst exhibited the highest CO₂ conversion of 84.3 % and nearly 100% CH₄ selectivity at 50000 ml g^‐1 h^‐1 and 420 °C. The enhancement effect of adding Fe on CO₂ methanation was attributed to the dual effect of suitable electronic environment and increased reducibility generated by Fe species.     

Epoxidation of cyclohexene with H2O2 over efficient water‐tolerant heterogeneous catalysts composed of mono‐substituted phosphotungstic acid on co‐functionalized SBA‐15

A series of Keggin‐type heteropolyacid‐based heterogeneous catalysts (Co‐/Fe‐/Cu‐POM‐octyl‐NH₃‐SBA‐15) were synthesized via immobilized transition metal mono‐ substituted phosphotungstic acids (Co‐/Fe‐/Cu‐POM) on octyl‐amino‐co‐functionalized mesoporous silica SBA‐15 (octyl‐NH₂‐SBA‐15). Characterization results indicated that Co‐/Fe‐/Cu‐POM units were highly dispersed in mesochannels of SBA‐15, and both types of Brønsted and Lewis acid sites existed in Co‐/Fe‐/Cu‐POM‐octyl‐NH₃‐SBA‐15 catalysts. Co‐POM‐octyl‐NH₃‐SBA‐15 catalyst showed excellent catalytic performance in H₂O₂‐mediated cyclohexene epoxidation with 83.8% of cyclohexene conversion, 92.8% of cyclohexene oxide selectivity, and 98/2 of epoxidation/allylic oxidation selectivity. The order of catalytic activity was Co‐POM‐octyl‐NH₃‐SBA‐15 > Fe‐POM‐octyl‐NH₃‐SBA‐15 > Cu‐POM‐octyl‐NH₃‐SBA‐15. In order to obtain insights into the role of ‐octyl moieties during catalysis, an octyl‐free catalyst (Co‐POM‐NH₃‐SBA‐15) was also synthesized. In comparison with Co‐POM‐NH₃‐SBA‐15, Co‐POM‐octyl‐NH₃‐SBA‐15 showed enhanced catalytic properties (viz. activity and selectivity) in cyclohexene epoxidation. Strong chemical bonding between ‐NH₃⁺ anchored on the surface of SBA‐15 and heteropolyanions resulted in excellent stability of Co‐POM‐octyl‐NH₃‐SBA‐15 catalyst, and it could be reused six times without considerable loss of activity.     

Nanostructured Catalyst for Fischer–Tropsch Synthesis

Fischer–Tropsch synthesis (FTS) is a heterogeneous catalytic process for the production of fuels or chemicals from synthesis gas (CO + H₂), which can be derived from nonpetroleum feedstocks such as natural gas, coal, or biomass. Co, Ru, Fe and Ni are all active in FTS, but only cheaper Fe and Co based catalysts are used in industry because the price of Ru is relatively high. However, the industrial Fe‐ and Co‐ based FTS catalysts normally work at a relatively high temperature range of 493—623 K in order to get a reasonable space time yield. Moreover, the product selectivity of FTS is governed by the law of polymerization, i.e., a so‐called Anderson‐Schulz‐Flory distribution holds, which restricts its industrial application. In this account, we highlight some of our progress toward the design/fabrication of nanostructured Fe, Co and Ru catalysts to improve FTS activity at the low temperature and to change the product selectivity and confine the product distribution into a certain range.     

An insight to the filtration mechanism of Pb(II) at the surface of a clay ceramic membrane through its preconcentration at the surface of a graphite/clay composite working electrode

The use of cyclic voltammetry (CV) and linear scan anodic stripping voltammetry (LSASV) to predict the selectivity of microfiltration ceramic membranes made from a lump of local clay towards Pb(II) ions filtration is described. The membranes were characterized by different techniques followed by CV analysis of the Fe(CN)₆^3-/Fe(CN)₆^4- redox couple and Pb(II) on bare graphite, raw clay, and clay-modified carbon paste electrode (clay-modified CPE). The effect of clay loading in the range of 1–10 % (w/w) on the electrodes is studied, where an enhanced peak current is observed for 5 % w/w clay. Moreover, a decrease in the peak current can be seen for bare graphite electrodes, suggesting that the clay mineral had played a substantial role in the sieving of heavy metal ions through the ceramic membrane. The electroactive surface area of 5% w/w raw clay towards Fe(II) ions was found to be in the order of 3.07 × 10^-2 cm² and higher than 5% w/w clay sintered to 1000 °C and bare graphite. CV analysis shows that both, 5 % w/w raw clay and 5 % w/w clay sintered to 1000 °C exhibited high peak currents towards Pb(II) ions. The mobility of the Pb(II) ions is found to increase when 5% w/w clay sintered to 1000 °C is utilized as membrane/electrode, leading to an increase in the amount of reduced Pb(II) ions on the surfaces of the clay membranes/electrodes. The study suggests successful filtration of Pb(II) ions through the proposed membrane/electrode and a much better accumulation than Fe(II) at the surface of the membrane/electrode before being subjected to filtration.     

Well-dispersed porous Fe–N–C catalyst towards the high-selective and high-efficiency conversion of CO2 to CO

In this study, through direct pyrolysis of a nitrogen-rich metal-organic framework of Fe-BTT at different temperatures and followed by acid treatment, we prepared a series of Fe–N–C_T (T = 800–1000 °C) composite catalysts with uniform cubic morphology and homogeneously distributed active sites. Acid leaching leads to the removal of excess Fe NPs and the exposure of more pyridinic N and porphyrin-like Fe–N_x sites and creates a higher specific surface area. Structural and electrochemical performance test results showed that Fe–N–C₉₀₀ catalyst exhibited the highest selectivity for CO product at –1.2 V vs. Ag/AgCl, with 496 mV of overpotential and 86.8% of Faraday efficiency, as well as excellent long-term stability, due to the good inheritance from rich-N Fe–BTT precursor.     

Controlled isoprene polymerization mediated by iminopyridine‐iron (II) acetylacetonate pre‐catalysts

A ligand controlled stereoselective polymerization of isoprene has been developed. A series of (aryl/alkyl)‐iminopyridine iron (II) acetylacetonate complexes: (aryl = Ph Fe1 ; alkyl = CH₂Ph Fe2 , CH (Ph)₂ Fe3 , CH (Me)₂ Fe4 , C (Me)₃ Fe5 , C (Me)₂CH₂C(Me)₃ Fe6 ), has been prepared in which steric and electronic substituents systematically modified to investigate their influences for isoprene polymerization. The molecular structure of representative complex Fe2 was confirmed by single crystal X‐ray diffraction and, revealed a distorted octahedral geometry at iron center. On treatment with methylaluminoxane (MAO), Fe1 – Fe6 displayed low ( Fe5 & Fe6 ) to high activities ( Fe1 – Fe4 ) with quantitative monomer conversion (>99%) for isoprene polymerization producing polyisoprene of high molecular weight (up to 2.0 × 10⁵ g/mol) and unimodal molecular weight distribution (1.4–3.3). Specifically, complex Fe2 (alkyl = CH₂Ph) displayed the highest activity of 7.0 × 10⁶ g (mol of Fe)^?1 h^?1 with 85% conversion of monomer over run time of 10 min at 25 °C. While, Fe6 catalyzed polyisoprene possessed high content of trans‐1,4 unit (up to 87%). Furthermore, the influence of the reaction parameters and the nature of the ligands on the catalytic activities and microstructural properties of the polymer were investigated in detail.     

Non-oxidative conversion of methane into various petrochemical grades over tunable tri-metallic Fe-W-Mo/HZSM-5 catalyst systems

Most mono-metallic catalysts applied in non-oxidative conversion of methane exhibit low catalyst activity and limited selectivity towards useful petrochemicals. In this study, a series of thermally stable and tunable 5.4 wt% metal/support Fe-W-Mo/HZSM-5 catalyst systems were synthesized, characterized, and applied in non-oxidative conversion of methane in a custom-made stainless-steel reactor at various process conditions. Analysis of products from the reactor was done using Shimadzu 2014 gas chromatograph. Varying the amount of Fe, W, and Mo on HZSM-5 greatly influenced catalyst activity in terms of methane conversion and product distribution. When the quantities of Fe and W were increased to 2.25 wt% each and the quantity of molybdenum reduced to 0.9 wt% in the overall 5.4 wt% metal/ HZSM-5 catalyst, the resultant catalyst system became most active in methane conversion (17.4%) at 800 °C. Reducing the quantity of Fe and W each to 1.35 wt% and increasing Mo to 2.7 wt% in the overall 5.4 wt% catalyst, the resultant catalyst system became less selective towards C₂ hydrocarbons and coke, but highly selective towards xylene and benzene. Therefore, this study demonstrates that varying metal loading presents an opportunity to tune the 5.4 wt% binary Fe, W, and Mo on HZSM-5 to achieve desired methane conversion and product distribution.     

Fe (III)‐grafted Bi2MoO6 nanoplates for enhanced photocatalytic activities on tetracycline degradation and HMF oxidation

Fe (III)‐grafted Bi₂MoO₆ nanoplates (Fe (III)/BMO) with varying small quantity of Fe (III) clusters modification were fabricated through a simple hydrothermal and impregnation process. The characterization results indicate that the modification of Fe (III) clusters on the surface of Bi₂MoO₆ nanoplates with intimate interfacial contact is beneficial to the expansion of visible light absorption range and the separation of photoinduced carriers during the interface charge transfer process. The photocatalytic properties of the samples were studied by degradation of tetracycline (TC) and selective aerobic oxidation of biomass‐derived chemical 5‐hydroxymethylfuraldehyde (HMF) under visible light. The 1.5 wt% Fe (III) clusters‐grafted Bi₂MoO₆ nanoplates exhibited optimum photocatalytic activity, which is the TC degradation kinetic rate constant is 5.3 times higher than that of bare BMO, and the highest HMF conversion of 32.62% can be obtained with a selectivity of 95.30%. Furthermore, a possible visible light photocatalysis mechanism over Fe (III)/BMO sample has been proposed. This study may supply some insight for the development of visible‐light‐driven Bi₂MoO₆‐based photocatalysts applicable to both environmental remediation and biomass‐derived chemical transformation.     

Novel Dendritic PNP Chromium Complexes: Synthesis,Characterization, and Performance on Ethylene Oligomerization

Three dendritic PNP ligands with ethylenediamine, 1,4‐butanediamine, 1,6‐diaminohexane as bridged groups are synthesized in good yields, respectively. Three dendritic PNP chromium complexes ( C1  –  C3 ) are prepared with the ligands and chromium(III ) chloride tetrahydrofuran complex (CrCl₃(THF )₃) as materials. The dendritic PNP ligands and the synthetic chromium complexes are fully characterized by spectroscopic and analytical methods. All chromium complexes activated with methylaluminoxane (MAO ) exhibited moderate activities on ethylene oligomerization (7.90 × 10⁴ – 2.15 × 10⁵ g (mol Cr h)⁻¹] and had better selectivity for C₆ and C₈ oligomer, reaching up to 81%. The chromium complex ( C1 ) activated with diethylaluminium chloride (Et₂AlCl) has higher catalytic activity than the chromium complex C1 activated with MAO , although the chromium complex ( C1 ) activated with Et₂AlCl had lower selectivity for C₆ and C₈ oligomer. The effects of solvent and reaction parameters on ethylene oligomerization are also studied using the chromium complex C1 as pre ‐ catalyst and MAO as co ‐ catalyst. Under optimized conditions ([complex] = 2 μmol, Al/Cr = 500, 25 °C, 0.9 MP a ethylene, 30 min), the catalytic activity of complex C1 in toluene is 2.15 × 10⁵ g (mol Cr h)⁻¹ and the selectivity for C₆ and C₈ oligomer is 36.76%. In addition, the structure of complexes significantly affects both the catalytic activity and the selectivity on ethylene oligomerization.     

Construction and characterization of nano iron complex ionophore for electrochemical determination of Fe(III) in pure and various real water samples

Electrochemical methods represent an important class of widely used techniques for the detection of metal ions. The unique chemical and physical properties of nanoparticles make them extremely suitable for designing new and improved sensing devices, especially electrochemical sensors and biosensors. This study focused on the synthesis of a nano‐Fe(III)–Sud complex and its characterization using various spectroscopic and analytical tools, optimized using the density functional theory method, screened for antibacterial activity and evaluated for possible binding to DNA using molecular docking study. Proceeding from the collected information, nano‐Fe(III)–Sud was used further for constructing carbon paste and screen‐printed ion‐selective electrodes. The proposed sensors were successfully applied for the determination of Fe(III) ions in various real and environmental water samples. Some texture analyses of the electrode surface were conducted using atomic force microscopy. At optimum values of various conditions, the proposed electrodes responded towards Fe(III) ions linearly in the range 2.5 × 10^?9–1 × 10^?2 and 1.0 × 10^?8–1 × 10^?2 M with slope of 19.73 ± 0.82 and 18.57 ± 0.32 mV decade^?1 of Fe(III) ion concentration and detection limit of 2.5 × 10^?9 and 1.0 × 10^?8 M for Fe(III)–Sud‐SPE (electrode I) and Fe(III)–Sud‐CPE (electrode II), respectively. The electrode response is independent of pH in the range 2.0–7.0 and 2.5–7.0, with a fast response time (4 and 7 s) at 25°C for electrode I and electrode II, respectively. Moreover, the electrodes also showed high selectivity and long lifetime (more than 6 and 3 months for electrode I and electrode II, respectively). The electrodes showed good selectivity for Fe(III) ions among a wide variety of metal ions. The results obtained compared well with those obtained using atomic absorption spectrometry.     

Solid-phase extraction of iron(III) with an ion-imprinted functionalized silica gel sorbent prepared by a surface imprinting technique

A new Fe(III)-imprinted amino-functionalized silica gel sorbent was prepared by a surface imprinting technique for selective solid-phase extraction (SPE) of Fe(III) prior to its determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). Compared with non-imprinted polymer particles, the ion-imprinted polymers (IIPs) had higher selectivity and adsorption capacity for Fe(III). The maximum static adsorption capacity of the ion-imprinted and non-imprinted sorbent for Fe(III) was 25.21 and 5.10 mg g⁻¹, respectively. The largest selectivity coefficient of the Fe(III)-imprinted sorbent for Fe(III) in the presence of Cr(III) was over 450. The relatively selective factor (α_r) values of Fe(III)/Cr(III) were 49.9 and 42.4, which were greater than 1. The distribution ratio (D) values of Fe(III)-imprinted polymers for Fe(III) were greatly larger than that for Cr(III). The detection limit (3σ) was 0.34 μg L⁻¹. The relative standard deviation of the method was 1.50% for eight replicate determinations. The method was validated by analyzing two certified reference materials (GBW 08301 and GBW 08303), the results obtained is in good agreement with standard values. The developed method was also successfully applied to the determination of trace iron in plants and water samples with satisfactory results.     

Highly fluorinated polymers with sulfonate,sulfamide and N,N‐diethylamino groups for the capillary electromigration separation of proteins and steroid hormones

Highly fluorinated polymers are promising materials in separation methods due to their combination of high chemical and thermally stability, hydro‐ and oleophobicity, and weak intermolecular forces. However, application of these polymers in chromatography is limited because of their low solubility in aqueous‐organic solvents. In our research, the highly fluorinated water soluble polymers with –SO₃⁻N(Et)₄⁺, –SO₂NH₂, and –N(Et)₂ terminal groups were synthesized and applied as additives to the background electrolyte for the separation of steroid hormones and proteins by capillary electromigration methods. It is shown that highly fluorinated polymers can be used both as pseudo‐stationary phases in electrokinetic chromatography for high separation efficiency (N  ∼ 200 × 10³) and selectivity (α  ∼  1.1) of uncharged analytes (e.g., steroid hormones), and as dynamic modifiers of fused silica capillary walls. The highest separation efficiency (N  ∼ 1 × 10⁶) and selectivity (α  ∼ 1.3) of steroid hormones was achieved by combination of sodium dodecyl sulfate and fluoropolymer with sulfonate groups in background electrolyte with pH 2. Dynamic wall coatings based on fluoropolymer with –SO₂NH₂ (which are easier and faster to create and wash off) exhibit significantly higher separation efficiency and selectivity compared to capillary electrochromatography on capillary columns based on polymethacrylate polymers.     

Insight into the role of iron in platinum-based bimetallic catalysts for selective hydrogenation of cinnamaldehyde

Selective hydrogenation of cinnamaldehyde (CAL) toward cinnamyl alcohol (COL) is an extremely important and challenging reaction. Herein, a series of Pt_xFe_y-Al₂O₃ bimetallic catalysts with varied Pt to Fe ratios were prepared by incipient wetness impregnation method. The introduction of Fe significantly modifies the electronic and surface properties of Pt, which clearly enhances the C=O hydrogenation selectivity. Among all the catalysts, Pt₃Fe-Al₂O₃ displays the best catalytic performance and the conversion of CAL is 96.6% with 77.2% selectivity of COL within 1 h. In addition, Pt₃Fe-Al₂O₃ had excellent reusability with 76% COL selectivity after five runs of the recycle process. Further characterization of the fresh, used and cycled catalysts revealed that the structure and electronic state of the synthesized Pt_xFe_y-Al₂O₃ are unchanged after hydrogenation reaction. The identical-location transmission electron microscopy (IL-TEM) results revealed that the interaction between the nanoparticles and the supports was strong and the catalyst was relatively stable.     

Photocatalytic Reduction of Greenhouse Gas CO2 to Fuel

Sun is the Earth’s ultimate and inexhaustible energy source. One of the best routes to remedy the CO₂ problem is to convert it to valuable hydrocarbons using solar energy. In this study, CO₂ was photocatalytically reduced to produce methanol, methane and ethylene in a steady-state optical-fiber reactor under artificial light and real sunlight irradiation. The photocatalyst was dip-coated on the optical fibers that enable the light to transmit and spread uniformly inside the reactor. The optical-fiber photoreactor, comprised of nearly 120 photocatalyst-coated fibers, was designed and assembled. The XRD spectra indicated the anatase phase for all photocatalysts. It is found that the methanol yield increased with UV light intensity. A maximum methanol yield of 4.12 μmole/g-cat h is obtained when 1.0 wt% Ag/TiO₂ photocatalyst was used under a light intensity of 10 W/cm². When mixed oxide, TiO₂–SiO₂, is doped with Cu and Fe metals, the resulting photocatalysts show substantial difference in hydrocarbon production as well as product selectivity. Methane and ethylene were produced on Cu–Fe loaded TiO₂–SiO₂ photocatalyst. Since dye-sensitized Cu–Fe/P25 photocatalyst can fully harvest the light energy of 400–800 nm from sunlight, its photoactivity was significantly enhanced. Finally, CO₂ photoreduction was studied by in situ IR spectroscopy and possible mechanism for the photoreaction was proposed.     

Synthesis,characterization, crystal structure determination and computational study of the high-spin iron(II) 2-cyanopyrazine complex trans-[Fe(pzCN)4Cl2]

A new mononuclear high-spin complex, trans-[Fe(pzCN)₄Cl₂] (1), was prepared from the reaction of FeCl₂.4H₂O and 2-cyanopyrazine (pzCN) in acetonitrile as a solvent. Suitable crystals of this complex for crystal structure determination were collected by slow evaporation of the produced pale orange solution. Complex 1 was characterized by elemental analysis (CHN), spectral methods (IR and UV–Vis), and single-crystal X-ray diffraction. The X-ray structural analysis indicated that the iron(II) is six-coordinated in an octahedral configuration by four N atoms from four 2-cyanopyrazine ligands and two chloride anions. Furthermore, the average of Fe–N bond lengths is 2.284(1)Å. It is well known that in the high-spin iron(II) phenanthroline and bipyridine complexes, the Fe–N bond lengths are around 2.2 Å. So, due to the Fe–N bond length in this complex, the iron(II) is unambiguously high-spin. The experimental evaluations on 1 have been complemented theoretically by the density functional theory (DFT) and TD-DFT calculations. The character of the Fe–N and Fe–Cl bonds was investigated using quantum theory of atoms in molecules. Additionally, electron delocalization and hyper-conjugative interactions of the synthesized complex were evaluated by natural bond orbital calculations.

     

Enhanced extract preparation of native manganese and iron species from brain and liver tissue

To date, no reference method for the extraction of labile Mn species from biological tissues is published which provides sufficient extraction efficiency combined with monitoring speciation. Here, an extraction method is reported using cryogenic conditions (+N) under inert gas atmosphere. Fresh brain and liver tissues were used, then stored either 1 day (+N) or 1 month in N_2liq (+N 1 m) to evaluate degradation effects during long-term storage. Both attempts were compared to a previous extraction method (−N) using neither N_2liq nor storage ability. Mn and Fe concentrations in extracts and pellets were determined with inductively coupled plasma (ICP)-atomic emission spectroscopy (AES) and compared to acid digests of the same sample. Element ratios of extracts/digest indicated the extraction efficiency, which was increased from 17% (−N) to 26% (+N) for Mn in brain or from 28% (−N) to 44% (+N) in liver extracts. For Fe species, the increase was only from 40% (−N) to 44% (+N) in brain but from 64% (−N) to 74% (+N) in liver. Size exclusion chromatography (SEC)-ICP-mass spectrometry (MS) was employed to screen for Mn and Fe species pattern in extracts. In brain, surplus extracted Mn (+N, +N 1 m) was assigned to organic Mn species, mainly from the 0.7–4 kDa fraction, while in the liver, it was seen in the 70–80 kDa fraction. Fe speciation was similar for −N and +N methods in brain extracts. In liver, higher amounts of Fe species were extracted from the 140–160 kDa fraction. Storage at −196 °C for 1 month did neither affect Mn speciation in brain nor in liver extracts. Fe species pattern showed a negligible shift (≤5%) from 140–160 to 70–80 kDa fraction in liver extracts stored 1 month in N_2liq.     

Ethylene Epoxidation over Alumina- and Silica-Supported Silver Catalysts in Low-Temperature AC Dielectric Barrier Discharge

In this work, ethylene epoxidation reaction for ethylene oxide production over silver catalysts loaded on two different supports (silica and alumina particles) in a low-temperature AC dielectric barrier discharge (DBD) reactor was investigated. The DBD plasma system was operated under the following base conditions: an O₂/C₂H₄ feed molar ratio of 1/4, a total feed flow rate of 50 cm³/min, an electrode gap distance of 0.7 cm, an input frequency of 500 Hz, and an applied voltage of 19 kV. From the results, the presence of silver catalysts improved the ethylene oxide production performance. The silica support interestingly provided a higher ethylene oxide selectivity than the alumina support. The optimum Ag loading on the silica support was found to be 20 wt%, exhibiting the highest ethylene oxide selectivity of 30.6%.     

Synthesis and structure of a dmpe-substituted dinuclear complex bridged by a substituent-free gallium atom: Electronic effect of metal fragment on the iron–gallium bonding

A dinuclear complex bridged by a substituent-free gallium atom, Cp¹(dmpe)Fe–Ga–Fe(CO)₄ (1b: Cp¹ = η-C₅Me₅, dmpe = Me₂PCH₂CH₂PMe₂), was synthesized by the reaction of Cp¹Fe(dmpe)GaCl₂ with K₂[Fe(CO)₄]. Crystal structure analysis of complex 1b showed that the geometry around the gallium atom is essentially linear and the two Fe–Ga bonds are significantly shorter than those of usual single bonds, indicating the multiple bonding character of the Fe–Ga bonds. Comparison of the structure and IR data of 1b and those of Cp¹(dppe)Fe–Ga–Fe(CO)₄ (1a: dppe = Ph₂PCH₂CH₂PPh₂) revealed that the Fe–Ga bond is sensitive to the electronic character of the metal fragment. The Fe–Ga bond is shortened upon introducing a more π-basic metal fragment.     

Sol–gel synthesis of Na<Subscript>2</Subscript>CaSiO<Subscript>4</Subscript> and its in vitro biological behaviors

In this work we prepared the hybrid material (SG) by the sol–gel method through the reaction between tetraethylortosilicate (TEOS) and acetylacetonatepropyltrimethoxysilane (ACACSIL). We also immobilized the acetylacetonate on silica surface (GR) by the grafting method through the reaction between a commercial silica and ACACSIL. Infrared thermal analysis showed that these materials were thermally stable until 200 °C. SG is a microporous material and has surface area of 500 m² g⁻¹, average porous volume of 0.09 cm³ g⁻¹ and organic content of 1 mmol g⁻¹. GR is a mesoporous material and has surface area of 300 m² g⁻¹, average porous volume of 0.7 cm³ g⁻¹ and organic content of 0.4 mmol g⁻¹. Iron(III) was coordinated to SG and GR resulting in the SG–Fe and GR–Fe silicas which were tested as catalysts on the aerobic epoxidation of cis-cyclooctene. SG–Fe yielded 100% of conversion and 94% of selectivity in epoxide whereas GR–Fe silica led to a maximum conversion of 50% and 100% of selectivity.     

Synthesis and characterization of Fe2O3/SiO2 nanocomposites

Fe₂O₃/SiO₂ nanocomposites based on fumed silica A-300 (S_BET = 337 m²/g) with iron oxide deposits at different content were synthesized using Fe(III) acetylacetonate (Fe(acac)₃) dissolved in isopropyl alcohol or carbon tetrachloride for impregnation of the nanosilica powder at different amounts of Fe(acac)₃ then oxidized in air at 400–900 °C. Samples with Fe(acac)₃ adsorbed onto nanosilica and samples with Fe₂O₃/SiO₂ including 6–17 wt% of Fe₂O₃ were investigated using XRD, XPS, TG/DTA, TPD MS, FTIR, AFM, nitrogen adsorption, Mössbauer spectroscopy, and quantum chemistry methods. The structural characteristics and phase composition of Fe₂O₃ deposits depend on reaction conditions, solvent type, content of grafted iron oxide, and post-reaction treatments. The iron oxide deposits on A-300 (impregnated by the Fe(acac)₃ solution in isopropanol) treated at 500–600 °C include several phases characterized by different nanoparticle size distributions; however, in the case of impregnation of A-300 by the Fe(acac)₃ solution in carbon tetrachloride only α-Fe₂O₃ phase is formed in addition to amorphous Fe₂O₃. The Fe₂O₃/SiO₂ materials remain loose (similar to the A-300 matrix) at the bulk density of 0.12–0.15 g/cm³ and S_BET = 265–310 m²/g.