Influence of the activation temperature on structural and textural properties of NiMo/Al2O3 hydrodesulfurization catalysts

Investigations of a commercial NiMo/Al₂O₃ hydrodesulfurization (HDS) catalyst are directed towards optimization of the activation procedure of HDS catalyst concerning active phase formation and thermal stability. Structural and textural data obtained with XRD, IR-FTIR, XPS and LTNA reveal that the optimal temperature for the formation of active species on the catalyst surface and an appropriate pore structure is 300°C.     

Combination of three analytical techniques for speciation of Al in environmental samples

An analytical scheme is proposed which combines three speciation techniques for determination of particular Al species in soil extracts and percolating waters. A cation-exchange fast protein liquid chromatography — inductively coupled plasma atomic emission spectrometry (FPLC-ICP-AES) procedure, a microcolumn chelating ion-exchange chromatography- atomic absorption spectrometry (MCC-ETAAS) technique and the 8-hydroxyquinoline spectrophotometric method (8HQ-spectrophotometry) were employed. The FPLC-ICP-AES procedure offers determination of Al³⁺ (retention time 4.5 min) and Al(OH)²⁺ species (retention time 4.0 min) which are separated from Al(OH)⁺ ₂ (retention time 1.5min). AlF²⁺ coelutes with Al(OH)²⁺ species, while Al(SO₄)⁺, AlF⁺ ₂ and negatively charged Al organic complexes coelute with Al(OH)⁺ ₂ species. The MCC-ETAAS technique enables determination of the sum of positively charged monomeric aqua- and hydroxy-Al species plus sulphate- and fluoro-Al complexes. Employing the 8HQ-spectrophotometry the sum of positively charged monomeric aqua- and hydroxy-Al species plus sulphato- and most of the labile organic Al species are determined. The sensitivities of these selected techniques were adequate for speciation of Al in the samples analyzed. On the basis of the specific selectivity of a particular technique various groups of Al species may be determined. Thus, the comparison of analytical data from complementary procedures provides more comprehensive information on Al species present in soil extracts and percolating waters.     

A Study of PbTiO3 Crystallization in Pure and Composite Nanopowders Prepared by the Sol-Gel Technique

Summary.  In this investigation the crystallization of PbTiO₃ upon annealing of pure nanopowders and PbTiO₃–SiO₂ (1:1 v/v) nanocomposite powders prepared by the sol-gel technique was studied. Using X-ray diffraction phase analysis, the start of PbTiO₃ crystallization in pure PbTiO₃ powders was detected at 400°C. Distinct crystallization of PbTiO₃ in PbTiO₃–SiO₂ nanocomposites starts at 700°C, whereas SiO₂ remains amorphous. There are indications that an interface interaction between the PbTiO₃ and the SiO₂ phase plays an important role in hindering the crystallization of PbTiO₃. The particle size (size of coherently scattering regions) was estimated from the broadening of the X-ray diffraction line profiles. The average size of PbTiO₃ nanocrystallites increases with temperature and time of annealing, the influence of temperature being more significant than that of the annealing time. Differential scanning calorimetry confirmed the results of the X-ray diffraction with respect to the start of the crystallization. Laser beam scattering and scanning electron microscopy provided the statistical distribution of the grain size and the morphology of the powder grains, showing that each grain of the powders contains several nanocrystallites (coherently scattering regions). Received October 4, 2001. Accepted (revised) December 14, 2001     

Bis(ammonium) fluorophosphate at room temperature

The title room‐temperature phase of (NH₄)₂(PO₃F) is orthorhombic (Pna2₁) and is related to the β‐K₂SO₄ structure family. The title structure consists of ammonium cations, NH₄⁺, and fluoro­phosphate anions, (PO₃F)^2?. These ions are connected by N—H?O hydrogen bonds. Two‐centre N—­H?F hydrogen bonds are not present in the structure. Phase transitions were detected at 251±2 and 274±2 K during cooling and heating, respectively.     

Mechanical and anti‐stabbing properties of modified thermoplastic polymers impregnated multiaxial p‐aramid fabrics

New forms of hybrid multiaxial nanocomposites with enhanced mechanical and stab resisting properties are presented. This study is motivated by the lack of knowledge in the study of the multiaxial fabric nanocomposites with two modified thermoplastic matrices for antiballistic protection. Introduction of 5 wt.% silica nanoparticles in the composite of polyurethane/p‐aramid/poly (vinyl butyral) leads to significant improvement in mechanical properties, and the addition of silane as a coupling agents and glutaraldehyde as a crosslinking agents yielded maximal values of storage modulus, tensile modulus and anti‐stabbing properties for hybrid nanocomposites. Ballistic resistance testing and penetration depth of the hybrid nanocomposites were visualized using image analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis, Characterization and Thermal Decomposition of Hydroxylammonium Uranyl Acetate

The synthesis of hydroxylammonium uranyl acetate is described. The identity of the synthesized compound was confirmed by chemical and infrared analysis. The intermediates and final products of the thermal decomposition were identified by means of thermogravimetric analysis, differential thermal analysis and X-ray diffraction. The thermal decomposition of hydroxylammonium uranyl acetate involves several steps. Two of them are due to decomposition of this compound to UO₂ via UO₂(CH₃COO)₂, and the third to the partial oxidation of UO₂ to UO₃ and the formation of U₂O₈ in the solid state at higher temperature.This revised version was published online in November 2005 with corrections to the Cover Date.     

Nonplanar graphs derived from Gauss codes of virtual knots and links

Virtual knot theory offers the possibility to consider knots and links embedded on different surfaces. This paper analyzes nonplanarity of graphs obtained from Gauss codes of virtual knots and links and their potential applications in chemistry.     

The use of fast protein liquid chromatography with ICP-OES and ES-MS-MS detection for the determination of various forms of aluminium in the roots of Chinese cabbage

The distribution of aluminium (Al) species was investigated in the roots of Al-tolerant Chinese cabbage (Brassica rapa L. ssp. pekinensis) by employing fast protein liquid chromatography (FPLC) with inductively coupled plasma optical emission spectrometry (ICP-OES) and electrospray tandem mass spectrometry (ES-MS-MS) detection. The cabbage was exposed to a nutrient solution that contained 10 μg cm⁻³ of Al³⁺. The results demonstrated that after 24 h of exposure, Al was quantitatively taken up by the cabbage and was distributed in different parts of the plant. 36 ± 6% of total Al was located in the roots, while the remaining 64 ± 10% was transferred to the leaves. It was found that in the roots Al was partially present in the root sap (15.5%), while the majority (84.5%) was accumulated in its apoplasmic compartments. It was further demonstrated that the proportion of Al that entered the symplasm formed a complex with organic acid. Speciation analysis by FPLC with ICP-OES detection and ES-MS-MS identification of the binding ligand indicated that Al-citrate complex was the prevailing species in the root sap.The results of the present study showed that both immobilization of Al in the apoplasmic compartments of the roots and transformation of Al³⁺ to Al-citrate are most likely responsible for the tolerance of Chinese cabbage (B. rapa L. ssp. pekinensis) to the toxic effects of Al³⁺.     

Design of self-cleaning TiO2 coating on clay roofing tiles

The phenomenon of heterogeneous photocatalysis takes place in the degradation process of many organic contaminants on solid surfaces. Photocatalysis is based on the excitation of the semiconductor by irradiation with supraband gap photons and the migration of electron-hole pairs to the surface of the photocatalysts, leading to the reaction of the holes with adsorbed H₂O and OH^? to form hydroxyl radicals. Due to the stability and photosensitivity of TiO₂ semiconductors, this system is well studied and is of great interest from an ecological and industrial point of view for use in the field of building materials. Clay roofing tiles, due to their long-term exploitation, are subject to physical, chemical and biological degradation that leads to deterioration. Ceramic systems have a high percentage of total porosity and considering their non-tolerance of organic coating, the use of surface active materials (SAM) that induce porosity in TiO₂ coatings is of vital significance. Photocatalytic coatings applied on clay roofing tiles under industrial conditions were designed by varying the quantity of TiO₂ (mass/cm²) on the tile surface (thin and thick TiO₂ layer). The positive changes in specific surface area and mesopore structure of the designed coatings were made by the addition of PEG 600 as a surface active material. It was shown that a thin photocatalytic layer (0.399 mg suspension/cm² tile surface), applied onto ceramic tiles under industrial conditions, had better photocatalytic activity in methylene blue decomposition, hydrophilicity and antimicrobial activity than a thick photocatalytic coating (0.885 mg suspension/cm²).     

Structural Snapshots of Cluster Growth from {U6} to {U38} During the Hydrolysis of UCl4

Herein we report the assembly of large uranium(IV) clusters with novel nuclearities and/or shapes from the controlled hydrolysis of UCl₄ in organic solution and in the presence of the benzoate ligands. {U₆}, {U₁₃}, {U₁₆}, {U₂₄}, {U₃₈} oxo and oxo/hydroxo clusters were isolated and crystallographically characterized. These structural snapshots indicate that larger clusters are slowly built from the condensation of octahedral {U₆} building blocks. The uranium/benzoate ligand ratio, the reaction temperature and the presence of base play an important role in determining the structure of the final assembly. Moreover, the isolation of different size cluster {U₆} (few hours), {U₁₆} (3 days), {U₂₄} (21 days) from the same solution in a chosen set of conditions shows that the assembly of uranium oxo clusters in hydrolytic conditions is time dependent.