Selective catalytic reduction of nitrogen monoxide with propene over CuCl/MCM-41 catalysts

Selective catalytic reduction of nitrogen monoxide with propene over two kinds of CuCl/MCM-41 catalysts prepared by a dispersion method has been studied. It was found that CuCl/AlMCM-41 exhibits substantially higher activity over CuCl/SiMCM-41. Characterization of these samples by H₂-TPR, IR and XRD showed that the active copper species were mainly related to Cu²⁺ and Cu⁺ ions in CuCl/AlMCM-41 catalyst.     

NaAlO2改性AlMCM-41：铝分布、酸量及催化性能的有效调控

以NaAlO2为改性剂是调控沸石骨架铝原子数量较常用且有效的方法.如杨春等[1]报道了用NaAlO2溶液对脱铝β沸石进行补铝,并通过XRD、吡啶吸附态红外光谱表征了铝化样品的特性;再者,谢在库[2]等以NaAlO2溶液对β沸石进行了改性,研究了β沸石酸性位及β沸石的补铝过程,并比较了铝化前后β沸石的催化活性.目前为止,虽以NaAlO2为改性剂铝化纯硅介孔材料的工作也有报道[3],但铝化步骤通常在低温(＜60℃)下进行,且对AlMCM-41的改性尚未涉及.     

Quantum Chemical Calculations on the Structure and Adsorption Properties of NO and N2O on Ag+ and Cu+ Ion-Exchanged Zeolites

Ab initio cluster quantum chemical calculations at the Hartree–Fock (HF/Lanl2dz) and correlated second-order Moller–Plesset perturbation theory (MP2/Lanl2dz) levels were performed for NO and N₂O interactions with Ag⁺ and Cu⁺ ion-exchanged zeolites. The interaction energies were estimated in a conventional way and also corrected for basis set superposition errors. It was shown that the highly dispersed Ag⁺ counterions establish twofold coordination to the lattice oxygens on the zeolite surface, similar to the case of Cu⁺ ions. However, both NO and N₂O bind relatively strongly to the Cu active sites of Cu⁺ ion-exchanged zeolites than those of the Ag⁺ site of the Ag⁺ ion-exchanged zeolites. Based on the results of these calculations, the two different forms of adsorption for these molecules on the catalyst surface, the nature of their binding and characteristics of the adsorption properties have been discussed. Finally, some comparisons with the results obtained by a variety of density functional theory calculations on target systems have been presented.     

Model-free kinetics applied for the removal of CTMA<Superscript>+</Superscript> and TPA<Superscript>+</Superscript> of the nanostructured hybrid AlMCM-41/ZSM-5 material

The nanostructured hybrid AlMCM-41/ZSM-5 composite was synthesized starting from a hydrogel with molar composition SiO₂:0.32Na₂O:0.03Al₂O₃:0.20TPABr:0.16CTMABr:55H₂O. The cetyltrimethylammonium bromide (CTMABr) and tetrapropylammonium bromide (TPABr) were used as templates. The above mentioned material presents morphological properties with specific characteristics, such as the surface area of the composite which is approximately half of the surface area of the conventional MCM-41. Another interesting feature is the formation of walls with the double of the density of the MCM-41 structure, which characterizes the hybrid material, resulting in a high stability material for catalytic application. The aim of this study is obtain optimized structures of the hybrid material and for this purpose variations in the synthesis time were carried out. A comparative analysis was performed including X-ray diffraction, Fourier transform infrared spectroscopy, and Thermogravimetry measurements. The model-free kinetic algorithms were applied in order to determinate conversion and apparent activation energy of the decomposition of the CTMA⁺ and TPA⁺ species from the hybrid AlMCM-41/ZSM-5.     

Ag Clusters as Active Species for HC-SCR Over Ag-Zeolites

The addition of hydrogen in the reaction atmosphere is effective in promoting the activity of Ag/alumina and Ag-zeolites on the selective reduction of NO by hydrocarbons (HC-SCR) at low temperatures. The increment of NO conversion over Ag-MFI corresponds to the periodic addition of hydrogen into C₃H₈-SCR conditions. The UV–VIS spectra of Ag-MFI have revealed that the addition of hydrogen results in the formation of Ag_n^δ+ clusters due to partial reduction and agglomeration of Ag species. The coincidence of the formation of the Ag_n^δ+ clusters and the increment of NO conversion suggests that Ag_n^δ+ clusters are the highly active species for HC-SCR. From analysis by H₂-TPR, UV–VIS, and EXAFS, the structure of Ag_n^δ+ clusters on Ag-MFI is identified as being Ag₄²⁺ on average. The formation of Ag clusters was strongly affected by the type of zeolites: The major Ag species are Ag⁺ ions for MOR, Ag_n^δ+ clusters for MFI and BEA, and relatively large metallic Ag_mparticles for Y. The sequence of Ag agglomeration (MOR < MFI < BEA < Y) is in accordance with the strength of the acid sites of zeolites. It can be expected that the interaction between the positive charge of Ag_n^δ+ clusters and acid sites, i.e., the ion-exchange site of zeolites, stabilizes Ag_n^δ+ clusters. The type of Ag species under HC-SCR conditions depends on the concentration of gas-phase oxidants (NO, O₂) and reductants (H₂, HC), and also on the number and strength of the zeolite acid sites.     

Azobenzene functionalized mesoporous AlMCM-41-type support for drug release applications

A light-responsive material, aminoazobenzene functionalized AlMCM-41, was synthesized and characterized in order to be used as carrier for drug delivery devices. The light-induced hydrophobic-hydrophilic switching effect of azobenzene functionalized aluminosilicate was exploited in the release of irinotecan, a cytostatic drug. To obtain the functionalized mesoporous support, an azobenzene-silane precursor was synthesized by coupling 4-(4′-aminophenylazo) benzoic acid with 3-aminopropyl triethoxysilane and further grafted on AlMCM-41. The azobenzene functionalized mesoporous aluminosilicate exhibited no significant toxicity towards murine fibroblast healthy cells and a reduced toxicity towards murine melanocyte cells. The hybrid materials obtained by loading irinotecan on AlMCM-41 (wt. 35.4%) and aminoazobenzene modified AlMCM-41 (wt. 22%), respectively were characterized by FTIR, small and wide angle XRD, N₂ adsorption-desorption isotherms and DSC analyses. A two-fold increase in the drug release rate from azobenzene functionalized aluminosilicate in phosphate buffer solution under UV irradiation was noticed, as compared with dark conditions. Moreover, the azobenzene functionalization of AlMCM-41 significantly increased the irinotecan delivery rate and total cumulative release in comparison with the pristine AlMCM-41 in similar conditions.

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A two‐dimensional network formed by self‐associating silver(I) perchlorate with 3‐[4‐(2‐thienyl)‐2H‐cyclopenta[d]pyridazin‐1‐yl]benzonitrile

In the organometallic silver(I) supramolecular complex poly[[silver(I)‐μ₃‐3‐[4‐(2‐thienyl)‐2H‐cyclopenta[d]pyridazin‐1‐yl]benzonitrile] perchlorate methanol solvate], {[Ag(C₁₈H₁₁N₃S)](ClO₄)·CH₃OH}_n, there is only one type of Ag^I center, which lies in an {AgN₂Sπ} coordination environment. Two unsymmetric multidentate 3‐[4‐(2‐thienyl)‐2H‐cyclopenta[d]pyridazin‐1‐yl]benzonitrile (L) ligands link two Ag^I atoms through π–Ag^I interactions into an organometallic box‐like unit, from which two 3‐cyanobenzoyl arms stretch out in opposite directions and bind two Ag^I atoms from neighboring box‐like building blocks. This results in a novel two‐dimensional network extending in the crystallographic bc plane. These two‐dimensional sheets stack together along the crystallographic a axis to generate parallelogram‐like channels. The methanol solvent molecules and the perchlorate counter‐ions are located in the channels, where they are fixed by intermolecular hydrogen‐bonding interactions. This architecture may provide opportunities for host–guest chemistry, such as guest molecule loss and absorption or ion exchange. The new fulvene‐type multidentate ligand L is a good candidate for the preparation of Cp–Ag^I‐containing (Cp is cyclopentadienyl) organometallic coordination polymers or supramolecular complexes.     

Kinetic parameters of surfactant remotion occluded in the pores of the AlMCM-41 nanostructured materials

A series of AlMCM-41 molecular sieves was synthesized starting from a hydrogel with the following molar composition: 1CTMABr:4.58SiO₂:(0.437 + X)Na₂O:XAl₂O₃:200H₂O. Tetramethylammonium silicate (TMAS) was used as silicon source and cethyltrimethylammonium bromide (CTMABr) was used as structure template. The obtained materials were characterized by nitrogen adsorption, XRD, FT-IR and TG/DTG. Model-free kinetic algorithms were applied in order to determinate conversion, isoconversion and apparent activation energy to decomposition of CTMA+ species from the AlMCM-41 materials with different silicon/aluminium (Si/Al) ratios of 20, 40, 60 and 80.     

Assembly of the Thiolated [Au1Ag22(S‐Adm)12]3+ Superatom Complex into a Framework Material through Direct Linkage by SbF6− Anions

Building framework materials with desirable properties and enhanced functionalities with nanocluster/superatom complexes as building blocks remains a challenge in the field of nanomaterials. In this study, the chiral [Au₁Ag₂₂(S‐Adm)₁₂]³⁺ nanocluster/superatom complex (SC, in which S‐Adm=1‐adamantanethiol) was employed as a building block to construct the three‐dimensional (3D) superatom complex inorganic framework (SCIF) materials SCIF‐1 and SCIF‐2 through inorganic SbF₆^? linkers. SCIF‐1 is racemic due to the assembly of two SC enantiomers in a single crystal. In SCIF‐2, the SC enantiomers are packed in separate crystals, thus producing larger channels and a circularly polarized luminescence (CPL) response. These two 3D SCIF materials exhibit unique sensitive photoluminescence (PL) in protic solvents. Our study provides a new pathway for creating novel open‐framework materials with superatom complexes and a foundation for the further development of 3D framework materials for sensing and other applications.     

Hydrodesulfurization of thiophene over CoMo/AlMCM-41

In this paper the application of a series of CoMo/AlMCM-41 catalysts with different Si/Al ratios was studied in the model reaction of thiophene hydrodesulfurization. The results obtained showed good catalytic activity for the formation of H₂S, isobutene, 1-butene, n-butane, 2-trans-butene-and 2-cis-butene.     

Ag+ selection by aza‐18‐crown‐6 ethers N‐Substituted on heterocyclic aromatics

Substitution on the nitrogen atom, where necessary by high‐pressure S_NAr reactions, of aza‐18‐crown‐6 ethers linked to heterocyclic aromatics has extended the number of potential host compounds for Ag⁺. The complexation of Ag⁺ by the new compounds has been evaluated by liquid membrane ion transport and ion extraction experiments. The nature of the binding sites of these new host compounds for Ag⁺ has been assessed, in DMF/D₂O (4/1), by ¹³C nmr titration experiments with AgClO₄.     

Solid-state ion-selective electrodes for the potentiometric determination of hexacyanoferrate (II)

Hexacyanoferrate(II)-sensing electrodes were prepared by mixing Ag₂S and Ag₄Fe (CN)₆. The 6:1 Ag₂S/Ag₄Fe (CN)₆ provided the best potentiometric response and speed of response. The log concentration vs. potential curves were linear with Nernstian slope (14.8 mV/decade) over the range 10^?1-10^?6 M hexacyanoferrate (II) at pH 7.00 with constant ionic strength. Interferences included iodide, sulfide and bromide. This electrode was used as indicator in potentiometric titrations of hexacyanoferrate (II).     

Single-fluorophore-based fluorescent probes enable dual-channel detection of Ag and Hg with high selectivity and sensitivity

A new type of fluorescent probe capable of detecting Ag⁺ and Hg²⁺ in two independent channels was developed in the present work. Specifically, in CH₃CN–MOPS mixed solvents with CH₃CN/MOPS ratio (v/v) of 15/85, this type of probe fluoresced weakly, and the addition of Ag⁺ remarkably induced fluorescence enhancement of the probe. In CH₃CN–MOPS mixed solvents with the percentage of CH₃CN increased up to 65%, the probe was highly fluorescent and addition of Hg²⁺ dramatically induced the fluorescence quenching. Thus, using such single-fluorophore-based probe and tuning the polarity of the mixed solvent, Ag⁺, and Hg²⁺ can be detected in independent channels with high selectivity and sensitivity. As a result, the mutual interference usually encountered in most cases of Ag⁺ and Hg²⁺ sensing owing to the similar fluorescence response that these two ions induced, can be effectively circumvented by using the probes developed herein.     

Study of the Adsorption Properties of MCM-41 Molecular Sieves Prepared at Different Synthesis Times

The variation of surface properties of SiMCM-41 and AlMCM-41 nanoporous materials as function of synthesis time was examined. The main properties studied were: surface area, pore diameter, pore volume, mesoporous parameter, and wall thickness. Siliceous MCM-41 molecular sieves were synthesized starting from hydrogels with the following molar compositions: 4.58SiO₂:0.435Na₂O:1 CTMABr:200 H₂O for SiMCM-41, and 4.58SiO₂:0.485 Na₂O:1 CTMABr:0.038 Al₂O₃:200 H₂O, for AlMCM-41. Cetyltrimethylammonium bromide (CTMABr) was used as the structural template. The crystallographic parameters were obtained from XRD data and by nitrogen adsorption using the BET and BJH methods. The results obtained showed a significant variation of the surface properties of the MCM-41 materials as a function of the synthesis time reaching silica wall thickness of ca. 2 nm on the fourth day.     

Ion-exchange synthesis and improved photovoltaic performance of CdS/Ag2S heterostructures for inorganic-organic hybrid solar cells

A facile ultrasound-assisted ion exchange route was developed for the synthesis of CdS/Ag₂S heterojunctions by ion exchange between the nanostructured CdS film and [Ag(NH₃)₂]⁺ under ultrasonication. The CdS/Ag₂S heterojunction film was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis DRS spectroscopy, photoelectrochemical measurements, and the transient photovoltage (TPV) technique. CdSAg₂S heterojunctions exhibit a dense morphology, enhanced visible light absorption and stronger photocurrent response than the pure CdS films. Poly(3-hexylthiophene) (P3HT) was then spin coated into the CdS/Ag₂S framework. Hybrid solar cells constructed with FTO/CdS/Ag₂S/P3HT/Au display relatively higher power conversion efficiency than FTO/CdS/P3HT/Au.     

Enhanced photoelectrochemical performance of Bi2S3/Ag2S/ZnO novel ternary heterostructure nanorods

The current work investigates the morphology, crystallinity and photoelectrochemical (PEC) performance of bismuth sulfide/silver sulfide/zinc oxide nanorods (Bi₂S₃/Ag₂S/ZnO NRAs) photoelectrodes as prepared at different annealing temperature. ZnO NRAs was initially grown hydrothermally, deposited in sequence with Ag₂S and Bi₂S₃ via successive ionic layer adsorption and reaction (SILAR) method before undergoing the annealing treatment. The optimised photoelectrode (Bi₂S₃/Ag₂S/ZnO NRAs-400 °C) possesses an optical bandgap of 1.60 eV extending the absorption edge of ZnO to visible light spectrum. The current-voltage characterization of Bi₂S₃/Ag₂S/ZnO NRAs photoelectrodes revealed that the photocurrent density and photoconversion efficiency were strongly dependent on the annealing temperature. The PEC study shows that the photoelectrode annealed at 400 °C achieved impressive photocurrent density of 12.95 mA/cm² at +0.5 V (vs Ag/AgCl/saturated KCl) under 100 mW/cm² illumination with superior photoconversion efficiency of 12.63%. This improvement is due to the cascade-designed band structure alignment of Bi₂S₃/Ag₂S/ZnO/ITO and to the brilliant role of Ag₂S as an intermediate layer that reduced random chance of electron-hole (e⁻_-h⁺) pairs recombination and improved the electrons collection efficiency. This work is highly anticipated to give contribution on further utilisation of Bi₂S₃/Ag₂S/ZnO NRAs as a promising semiconductor material in PEC related applications.     

Selective Catalytic Reduction of Nitric Oxide by Ammonia over Ag and Zn‐Exchanged Cuban Natural Zeolites

The catalytic selective reduction of NO over metal‐exchanged (Zn^II, Ag^I) natural zeolites (mordenite and clinoptilolite) from Cuba using NH₃ as a reducing agent in the presence of excess oxygen was studied. Both transition metals slightly improve the catalytic performance for the NO reduction. Zn^II‐exchanged zeolites exhibit a moderate catalytic activity, with conversions of NO of ≈58 % and high selectivity to N₂ at high temperatures.     

Photochemical properties of Ag ion clusters included within ZSM-5 zeolites prepared by an ion-exchange method

Photoluminescence investigations of the Ag ion-exchanged ZSM-5 (Ag⁺ /ZSM-5) zeolite revealed that a Ag ion cluster (Agⁿ _m ⁺) exists in the pore structure of ZSM-5 exhibiting photoluminesm cence at 380 nm upon excitation at 332 nm. UV irradiation ( = 285 nm) of Ag⁺ /ZSM-5 at 77 K leads to the transformation of Agⁿ _m ⁺ into a different Ag ion cluster (Ag_m ^(n-1)+) which exhibits photoluminescence at 465 nm upon excitation at 315 nm. This photo-transformation of the Ag ion clusters was found to be thermally reversible under vacuum. It was demonstrated that an electron transfer from the photo-excited Al³⁺ -O^2- to Agⁿ _m ⁺ plays a significant role in this process. In the presence of oxygen, UV irradiation of Ag⁺ /ZSM-5 leads to the formation of O₂- instead of an Ag ion cluster (Ag_m ^(n-1)+), suggesting that oxygen acts as an efficient electron scavenger, which interferes with the electron capture of Agⁿ _m ⁺ under UV irradiation at 285 nm.     

反应性模板法合成硫化银中空球-银纳米粒子异质结构

以Cu₂S中空球为反应性模板, 通过在水溶液中与银离子的阳离子交换和氧化还原反应制备了大小均匀的Ag₂S中空球-Ag纳米粒子异质结构, 即Ag₂S-Ag异质中空球. 该异质结构中每个Ag₂S中空球的直径约为600 nm, 壁厚约20–30 nm, 其表面均附着一个Ag纳米粒子. 采用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射(XRD)和能量色散X射线谱(EDS)对所得Ag₂S-Ag异质中空球的结构和组成进行了表征. 若以CuS中空球为反应性模板, 在相似转化条件下则主要得到不含Ag粒子的Ag₂S中空球. 该结果表明, Cu₂S中的Cu(I)的还原性在Ag₂S-Ag异质中空球的形成中发挥了重要作用. 通过对所制备的Ag₂S-Ag异质中空球进行二次生长, 还可以得到Ag₂S中空球的半球表面均被Ag膜所包覆的Ag₂S-Ag异质中空球.     

Biomimetic synthesis of the arachidic acid/Ag<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>S nanocomposite films

Ag _x Cd _y S nanoparticles were obtained in arachidic acid (AA) monolayer containing Ag⁺ and Cd²⁺ under H₂S flow. The AA/Ag _x Cd _y S monolayers were deposited onto solid substrate to prepare LB films. The UV-vis spectrum showed that the LB film exhibited notable quantum-size effect. The small-angle X-ray diffraction revealed periodic structure of the LB films. The molar ratio of Ag to Cd in AA/Ag _x Cd _y S film was ca. 1 : 5 as measured by the XPS. TEM and FTIR spectroscopy showed that the head-groups of arachidic acid molecules controlled formation of Ag _x Cd _y S nanoparticles in the monolayer.