Experimental Evidence of the Mechanism of Selective Catalytic Reduction of NO with NH3 over Fe-Containing BEA Zeolites

Various temperature-programmed techniques were used as tools in mechanistic studies of selective catalytic reduction (SCR) of NO with ammonia in the presence of Fe-containing BEA zeolites. Moreover, FTIR studies of adsorbed NH₃ and NO were conducted to determine the interactions of reactants with the catalyst surface. Iron was introduced into BEA zeolite by three different methods: i) two-step post-synthesis; ii) conventional wet impregnation; iii) ion exchange. The catalytic activity was dependent on the method used for iron introduction. The reactivities of NH₃ and NO adsorbed on iron-modified zeolites obtained by impregnation and ion-exchange methods were higher than those measured for the catalyst obtained by a two-step post-synthesis method. The activity of Fe-containing zeolites in SCR was related to the form of deposited iron species, as well as to the nature, strength, and concentration of acid sites. Possible reaction pathways of NO reduction over the FeBEA zeolite catalysts were presented and discussed.

Iron-Based Metal-Organic Frameworks as a Theranostic Carrier for Local Tuberculosis Therapy

PURPOSE

The purpose of the study was initial evaluation of applicability of metal organic framework (MOF) Fe-MIL-101-NH2 as a theranostic carrier of antituberculous drug in terms of its functionality, i.e. drug loading, drug dissolution, magnetic resonance imaging (MRI) contrast and cytotoxic safety.

METHODS

Fe-MIL-101-NH2 was characterized using X-ray powder diffraction, FTIR spectrometry and scanning electron microscopy. The particle size analysis was determined using laser diffraction. Magnetic resonance relaxometry and MRI were carried out on phantoms of the MOF system suspended in polymer solution. Drug dissolution studies were conducted using Franz cells. For MOF cytotoxicity, commercially available fibroblasts L929 were cultured in Eagle's Minimum Essential Medium supplemented with 10% fetal bovine serum.

RESULTS

MOF particles were loaded with 12% of isoniazid. The particle size (3.37-6.45 μm) depended on the micronization method used. The proposed drug delivery system can also serve as the MRI contrast agent. The drug dissolution showed extended release of isoniazid. MOF particles accumulated in the L929 fibroblast cytoplasmic area, suggesting MOF release the drug inside the cells. The cytotoxicity confirmed safety of MOF system.

CONCLUSIONS

The application of MOF for extended release inhalable system proposes the novel strategy for delivery of standard antimycobacterial agents combined with monitoring of their distribution within the lung tissue.

Characterization of Co and Fe-MCM-56 catalysts for NH3-SCR and N2O decomposition: An in situ FTIR study

Two-step preparation of iron and cobalt-containing MCM-56 zeolites has been undertaken to evaluate the influence of their physicochemical properties in the selective catalytic reduction (NH₃-SCR or DeNOx) of NO using NH₃ as a reductant. Zeolites were prepared by the selective leaching of the framework cations by concentrated HNO₃ solution and NH₄F/HF mixture and consecutively, introduction of Co and Fe heteroatoms, in quantities below 1wt%. Further calcination allowed to obtain highly dispersed active species. Their evaluation and speciation was realized by adsorption of pyridine and NO, followed by FTIR spectroscopy. Both Fe-MCM-56 zeolites showed excellent activities (maximum NO conversion 92%) with high selectivity to dinitrogen (above 99%) in the high temperature NH₃-SCR process. High catalytic activity of Fe-MCM-56 zeolites was assigned to the formation of stable nitrates, delivering NO to react with NH₃ at higher temperatures and suppressing the direct NO oxidation. It was found that more nitrates was formed in Fe-MCM-56 (HNO₃) than in Fe-MCM-56 (HF/NH₄F) and that could compensate for the lower Fe loading, resulting in very similar catalytic activity of both catalysts. At the same time both Co-and Fe-MCM-56 zeolites were moderately active in direct N₂O decomposition, with maximum N₂O conversion not higher than 80% and activity window starting at 500°C. This phenomenon was expected since both types of catalysts contained well dispersed active centers, not beneficial for this reaction.

Pillaring of layered zeolite precursors with ferrierite topology leading to unusual molecular sieves on the micro/mesoporous border

Layered zeolite materials with FER layer topology can produce various condensed and expanded structures including zeolite frameworks, FER and CDO, their interlayer expanded forms (IEZ), and organic-intercalated and pillared derivatives. This work concerns pillaring of the surfactant-swollen derivative with a gallery height of ca. 2.5 nm between layers by treatment with tetraethylorthosilicate (TEOS) at room and elevated temperatures. The materials obtained at 100 °C and higher showed unusual properties including 2 nm pores on the micro/mesoporous border and disordered layer packing indicated by the absence of distinct low angle interlayer peaks at d-spacing >3 nm (∼3° 2θ Cu Kα radiation) in the X-ray diffraction pattern (XRD). TEOS treatment at room temperature produced a pillared molecular sieve with the expected mesoporous characteristics, namely a pore size of around 3 nm and a high intensity low angle (001) peak at 2.3° 2θ, and a d-spacing of 3.8 nm, in the XRD. The characterization aiming to elucidate the nature of the obtained unusual products included gas adsorption isotherms, aberration corrected (C_s-corrected) Scanning Transmission Electron Microscopy (STEM) studies and ²⁹Si solid state NMR. BET surface area values decreased with the temperature of TEOS treatment from approximately 1200 m² g^-1 to ∼900 and 600 m² g^-1, at room temperature, 100 °C, and 120 °C, respectively. The ²⁹Si solid state NMR revealed the presence of both Q³ ((SiO)₃SiOX, X = H or minus charge) and Q⁴ ((SiO)₄Si) centers giving separated signals up to the pillaring step. After pillaring at 100 °C and calcination, the nominal intensity ratios Q⁴ : Q³ were 2.17 and 2.61 but the signals were merged into one broad peak indicating the structural heterogeneity of Si-O coordination. The microscopy showed the presence of FER layers in the samples but the overall structure and composition were not well-defined. The observed unusual disorganization and possible partial degradation of layers during pillaring may result from the combination of high temperature, alkalinity (surfactant hydroxide) and siliceous composition of the layers. The obtained pillared products are of interest for the preparation of larger pore catalysts and sorbents or controlled drug delivery.

Isotope engineering of van der Waals interactions in hexagonal boron nitride

Hexagonal boron nitride is a model lamellar compound where weak, non-local van der Waals interactions ensure the vertical stacking of two-dimensional honeycomb lattices made of strongly bound boron and nitrogen atoms. We study the isotope engineering of lamellar compounds by synthesizing hexagonal boron nitride crystals with nearly pure boron isotopes (¹⁰B and ¹¹B) compared to those with the natural distribution of boron (20 at% ¹⁰B and 80 at% ¹¹B). On the one hand, as with standard semiconductors, both the phonon energy and electronic bandgap varied with the boron isotope mass, the latter due to the quantum effect of zero-point renormalization. On the other hand, temperature-dependent experiments focusing on the shear and breathing motions of adjacent layers revealed the specificity of isotope engineering in a layered material, with a modification of the van der Waals interactions upon isotope purification. The electron density distribution is more diffuse between adjacent layers in ¹⁰BN than in ¹¹BN crystals. Our results open perspectives in understanding and controlling van der Waals bonding in layered materials.

The microstructure, local indium composition and photoluminescence in green-emitting InGaN/GaN quantum wells

In this work, we analyse the microstructure and local chemical composition of green-emitting In_x Ga_1-x N/GaN quantum well (QW) heterostructures in correlation with their emission properties. Two samples of high structural quality grown by metalorganic vapour phase epitaxy (MOVPE) with a nominal composition of x = 0.15 and 0.18 indium are discussed. The local indium composition is quantitatively evaluated by comparing scanning transmission electron microscopy (STEM) images to simulations and the local indium concentration is extracted from intensity measurements. The calculations point out that the measured indium fluctuations may be correlated to the large width and intensity decrease of the PL emission peak.

Layer like porous materials with hierarchical structure

Many chemical compositions produce layered solids consisting of extended sheets with thickness not greater than a few nanometers. The layers are weakly bonded together in a crystal and can be modified into various nanoarchitectures including porous hierarchical structures. Several classes of 2-dimensional (2D) materials have been extensively studied and developed because of their potential usefulness as catalysts and sorbents. They are discussed in this review with focus on clays, layered transition metal oxides, silicates, layered double hydroxides, metal(iv) phosphates and phosphonates, especially zirconium, and zeolites. Pillaring and delamination are the primary methods for structural modification and pore tailoring. The reported approaches are described and compared for the different classes of materials. The methods of characterization include identification by X-ray diffraction and microscopy, pore size analysis and activity assessment by IR spectroscopy and catalytic testing. The discovery of layered zeolites was a fundamental breakthrough that created unprecedented opportunities because of (i) inherent strong acid sites that make them very active catalytically, (ii) porosity through the layers and (iii) bridging of 2D and 3D structures. Approximately 16 different types of layered zeolite structures and modifications have been identified as distinct forms. It is also expected that many among the over 200 recognized zeolite frameworks can produce layered precursors. Additional advances enabled by 2D zeolites include synthesis of layered materials by design, hierarchical structures obtained by direct synthesis and top-down preparation of layered materials from 3D frameworks.

Phonon-Photon Mapping in a Color Center in Hexagonal Boron Nitride

We report on the ultraviolet optical response of a color center in hexagonal boron nitride. We demonstrate a mapping between the vibronic spectrum of the color center and the phonon dispersion in hexagonal boron nitride, with a striking suppression of the phonon assisted emission signal at the energy of the phonon gap. By means of nonperturbative calculations of the electron-phonon interaction in a strongly anisotropic phonon dispersion, we reach a quantitative interpretation of the acoustic phonon sidebands from cryogenic temperatures up to room temperature. Our analysis provides an original method for estimating the spatial extension of the electronic wave function in a point defect.

Framework-substituted cerium MCM-22 zeolite and its interlayer expanded derivative MWW-IEZ

Framework-substituted MCM-22 with up to 5% Ce was prepared by a conventional non-TEOS-based method.

Adsorptive desulfurization with CPO-27/MOF-74: an experimental and computational investigation

By combining experimental adsorption isotherms, microcalorimetric data, infrared spectroscopy and quantum chemical calculations the adsorption behaviour of the CPO-27/MOF-74 series (Ni, Co, Mg, Cu, and Zn) in the desulfurization of fuels is evaluated.

Application of quasi-equilibrated thermodesorption of linear and di-branched paraffin molecules for detailed porosity characterization of the mono-layered zeolite MCM-56, in comparison with MCM-22 and ZSM-5

Thermodesorption of 2,2-dimethyloctane reveals different content of subsurface micropores in MWW-type zeolites.

[Hip fracture, antiplatelet drugs treatment and postoperative complications]

OBJECTIVES

To assess the incidence of postoperative complications, blood transfusions and survival at one month, in the old patients operated for hip fracture undergoing chronic treatment with antiplatelet drugs.

MATERIAL AND METHODS

Two hundred twenty three patients operated for hip fracture were studied retrospectively, separated into 3 groups: patients who received acetylsalicylic acid (group I), patients who were given 100mg/day of acetylsalicylic acid or 300mg/day of triflusal (group II) and patients receiving>100mg/day of acetylsalicylic acid, or>300mg/day of triflusal or thienopyridines (group III). Surgery was delayed for 4 days in patients in group III. Demographic, biological, clinical and treatment characteristics, postoperative complications and survival at one month were recorded.

RESULTS

Patients in group III were older and sustain worse general health status. Patients with a higher transfusion requirement were those of group II (73.8%) (P=0.192), who also showed a higher percentage of anaemia on admission. Severe cardiovascular complications were experienced by 5.4% of group III patients, 4.8% of group II patients and 2.1% of group I patients. Patients from group III presented a significant amount of respiratory complications (P=0.007).

CONCLUSIONS

Our results suggest that delaying surgery for 4 days in patients treated with clopidogrel can be associated to an increase in postoperative respiratory complications and severe adverse cardiovascular events, without increasing the tranfusional index, hospital stay, mortality, and without complications related to neuraxial anaesthesia.