Correction: Crystal structure and microstructural changes of molybdenum nitrides traces during catalytic reaction by in situ X-ray diffraction studies. (Correction)

X-ray diffraction was used to study changes in the crystal structure and microstructure of molybdenum nitrides during ammonia decomposition. In addition, electron microscopy was employed to analyse morphological changes of the nitrides caused by the catalytic reaction. Molybdenum nitride catalysts (MoxNy) were prepared via high temperature ammonolysis of molybdenum oxide (MoO3) at 650 °C and 800 °C. The materials are nanocrystalline and highly porous, the samples produced at 650 °C still contain the partly reduced precursor (MoO2). In situ X-ray diffraction studies performed on a laboratory instrument equipped with a catalysis reaction chamber reveal significant compositional and structural changes taking place during the reaction. Ball milling, known to enhance the activity of catalysts, has a deleterious effect on the molybdenum nitride specimens: it gives an initial boost due to the reduction of size and increase in dislocation content, but it also favours the formation of the less active hexagonal MoN

Crystal structure and microstructural changes of molybdenum nitrides traced during catalytic reaction by in situ X-ray diffraction studies

X-ray diffraction was used to study changes in the crystal structure and microstructure of molybdenum nitrides during ammonia decomposition. In addition, electron microscopy was employed to analyse morphological changes of the nitrides caused by the catalytic reaction. Molybdenum nitride catalysts (MoxNy) were prepared via high temperature ammonolysis of molybdenum oxide (MoO3) at 650 °C and 800 °C. The materials are nanocrystalline and highly porous, the samples produced at 650 °C still contain the partly reduced precursor (MoO2). In situ X-ray diffraction studies performed on a laboratory instrument equipped with a catalysis reaction chamber reveal significant compositional and structural changes taking place during the reaction. Ball milling, known to enhance the activity of catalysts, has a deleterious effect on the molybdenum nitride specimens: it gives an initial boost due to the reduction of size and increase in dislocation content, but it also favours the formation of the less active hexagonal MoN

Molybdenum-based catalysts for the decomposition of ammonia: In situ X-ray diffraction studies, microstructure, and catalytic properties

The ammonia decomposition reaction over molybdenum-based catalysts is an example for the complex influence of different factors, such as phase composition; size of crystalline domains, or defect concentration, on the catalytic behavior of a material. In situ powder diffraction allows the direct analysis of how catalysts change during a reaction with respect to the atomic structure or microstructure in terms of defects or size changes. In this article, the influence of catalyst treatment such as pre-reduction or ball milling on the catalytic properties is discussed in detail

Copper(II)salen catalysed, asymmetric synthesis of \u3b1,\u3b1- disubstituted amino acids

Cu(salen) complex 1 was found to be a versatile catalyst for the asymmetric alkylation of a range of enolates derived from \u3b1-amino acids, leading to \u3b1,\u3b1-disubstituted amino acids. The enantioselectivity of the process decreases as the size of the amino acid sidechain increases, but functionalized amino acids such as allylglycine and aspartic acid are substrates for the process. Benzylic bromides are found to be more enantioselective alkylating agents than propargylic bromides. As an example of the utility of this chemistry, an \u3b1-propargylic allylglycine derivative is prepared and subjected to ene-yne metathesis using Grubbs' catalyst to give a non-racemic cyclopentenyl amino acid. \ua9 2003 Elsevier Ltd. All rights reserved

Study of the effect of organically functionalyzed silica nanoparticles on the properties of uv curable acrylic coatings

In this work the properties of UV curable coatings were improved modifying the polymeric matrix adding properly functionalized silica inorganic nanoparticles. Mild steel sheets were used as substrate. Pre-formed silica nanoparticles, prepared by sol–gel chemistry from methyltriethoxysilane (MTES) and methacryloxypropyltrimethoxysilane (MPTMS) precursors, were dispersed into UV curable acrylic oligomers: by irradiation a polymeric matrix embedding the nanoparticles was obtained. Unfilled UV cured coatings were also produced for comparison. The DSC measurements revealed different thermal stabilities among the samples, depending on the presence of the functionalized nanoparticles. The barrier properties (investigated by means of electrochemical impedance spectroscopy, EIS) were demonstrated to be strongly affected by the presence of the nanoparticles. In particular, a proper functionalization of the silica nanoparticles leads to noticeable improvement of the barrier properties of the coatings against ions permeation. The effect of the functionalized nanoparticles on the coating properties was also investigated performing water vapor diffusion measurements through the different coatings. The experimental measurements highlighted that the appropriate functionalization of the silica particles leads to noticeable improvements of the barrier properties against water and ions permeation of the composite polymeric coating with respect to the unfilled UV curable resin

Hybrid organic/inorganic materials for photonic applications via assembling of nanostructured molecular units

International audienceHybrid organic–inorganic materials exhibit so versatile properties that they can be considered one of the most interesting classes of materials for photonic applications, for the development of both passive and active devices. A synthetic route used for the preparation of nanostructured organic/inorganic (O/I) materials is the assembling of nano-building blocks (NBBs). This approach allows controlling the extent of phase interaction, which in its turn governs the structure-properties relationships. The non-hydrolytic sol–gel process is recognized as a useful route for the preparation of nanostructured molecular units. The condensation reaction of methacryloxypropyl trimethoxysilane and diphenylsilanediol in a non-hydrolytic sol–gel process has been exploited in order to synthesize nanostructured molecular units for the preparation of hybrid organic/inorganic coatings. The non-hydrolytic condensation reactions were run adding different compounds such as triethylamine, titanium isopropoxide, titanium chloride, and dibutyldilauryltin as condensation promoters. The NBB synthesis was also run under controlled hydrolitic conditions, by exploiting the in situ water production using an ethanol/acetic acid mixture. These reactions have been compared in terms of the influence of the employed reagents on the condensation degree and the product structure. Multinuclear NMR, ATR-FTIR and FT-Raman techniques have been used to study the reaction steps and characterize the final condensation products. Hybrid O/I materials have been prepared by assembling methacrylate-based NBBs in the presence of suitable thermal and photo-initiators. The study on the progress of the thermal polymerization process using differential scanning calorimetry (DSC) will be presented, as well as the preliminary results on the two photon polymerization (TPP) process for the preparation of patternable films

Photopolymerization of hybrid organic/inorganic materials based on nanostructured units for photonic applications

In this work we report on the study of the photopolymerization process in hybrid organic-inorganic films containing photopolymerizable acrylic and methacrylic groups and. The films are doped with a proper photo-initiator for radical polymerization of (meth)acrylic units and are prepared using the sol-gel technique. The photo-initiator is activated by using continuum (single-photon polymerization) or pulsed (two-photon polymerization) laser sources at different wavelengths. After the development of the unexposed regions with a suitable solvent, the photopolymerized structures are observed with microscopy techniques. The effects of the composition of the photopolymerizable mixture, the irradiation parameters (laser power and exposure time) and the external atmosphere in which the photopolymerization is performed are investigated. The fabrication of 3D microstructures using multiphoton absorption processes is a promising technique that involves low amount of incident exposure dose with potentially high spatial resolutio