Synthesis of palladium nanoparticles over graphite oxide and carbon nanotubes by reduction in ethylene glycol and their catalytic performance on the chemoselective hydrogenation of para-chloronitrobenzene

Pd nanoparticles have been synthesized over carbon nanotubes (CNT) and graphite oxide (GO) by reduction with ethylene glycol and by conventional impregnation method. The catalysts were tested on the chemoselective hydrogenation of p-chloronitrobenzene and the effect of the synthesis method and surface chemistry on their catalytic performance was evaluated. The catalysts were characterized by N2 adsorption/desorption isotherms at 77 K, TEM, powder X-ray diffraction, thermogravimetry, infrared and X-ray photoelectron spectroscopy and ICP-OES. It was observed that the synthesis of Pd nanoparticles employing ethylene glycol resulted in metallic palladium particles of smaller size compared to those prepared by the impregnation method and similar for both supports. The presence of oxygen groups on the support surface favored the activity and diminished the selectivity. It seems that ethylene glycol reacted with the surface groups of GO, this favoring the selectivity. The activity was higher over the CNT-based catalysts and both catalysts prepared by reduction in ethylene glycol were quite stable upon recycling.

Síntese e caracterização de catalisadores de LaNiO3 não suportados e suportados em Al2O3 e ZrO2 para a reforma a vapor do metano

Ionic oxides with ABO3 structure, where A represents a rare earth element or an alkaline metal and B is a transition metal from group VIII of the periodic table are potential catalysts for oxidation and good candidates for steam reforming reaction. Different methods have been considered for the synthesis of the oxide materials with perovskite structure to produce a high homogeneous material with low amount of impurities and low calcination temperatures. In the current work, oxides with the LaNiO3 formula had been synthesized using the method of the polymeric precursors. The thermal treatment of the materials took place at 300 ºC for 2h. The material supported in alumina and/or zirconia was calcined at 800 ºC temperature for 4h. The samples had been characterized by the following techniques: thermogravimetry; infrared spectroscopy; X-ray diffraction; specific surface area; distribution of particle size; scanning electron microscopy and thermo-programmed reduction. The steam reforming reaction was carried out in a pilot plant using reducing atmosphere in the reactor with a mixture of 10% H2-Argon, a mass about 5g of catalyst, flowing at 50 mL.min-1. The temperature range used was 50 - 1000 oC with a heating rate of 10 oC.min-1. A thermal conductivity detector was used to analyze the gas after the water trapping, in order to permit to quantify the consumption of hydrogen for the lanthanum nickelates (LaNiO3). The results showed that lanthanum nickelate were more efficient when supported in alumina than when supported in zirconia. It was observed that the methane conversion was approximately 100% and the selectivity to hydrogen was about 70%. In all cases were verified low selectivity to CO and CO2

Ihwg-μnir: A Miniaturised Near-infrared Gas Sensor Based On Substrate-integrated Hollow Waveguides Coupled To A Micro-nir-spectrophotometer.

A miniaturised gas analyser is described and evaluated based on the use of a substrate-integrated hollow waveguide (iHWG) coupled to a microsized near-infrared spectrophotometer comprising a linear variable filter and an array of InGaAs detectors. This gas sensing system was applied to analyse surrogate samples of natural fuel gas containing methane, ethane, propane and butane, quantified by using multivariate regression models based on partial least square (PLS) algorithms and Savitzky-Golay 1(st) derivative data preprocessing. The external validation of the obtained models reveals root mean square errors of prediction of 0.37, 0.36, 0.67 and 0.37% (v/v), for methane, ethane, propane and butane, respectively. The developed sensing system provides particularly rapid response times upon composition changes of the gaseous sample (approximately 2 s) due the minute volume of the iHWG-based measurement cell. The sensing system developed in this study is fully portable with a hand-held sized analyser footprint, and thus ideally suited for field analysis. Last but not least, the obtained results corroborate the potential of NIR-iHWG analysers for monitoring the quality of natural gas and petrochemical gaseous products.

Prediction of processed cheese instrumental texture and meltability by mid-infrared spectroscopy coupled with chemometric tools

The objective of this study was to determine the potential of mid-infrared spectroscopy coupled with multidimensional statistical analysis for the prediction of processed cheese instrumental texture and meltability attributes. Processed cheeses (n = 32) of varying composition were manufactured in a pilot plant. Following two and four weeks storage at 4 degrees C samples were analysed using texture profile analysis, two meltability tests (computer vision, Olson and Price) and mid-infrared spectroscopy (4000-640 cm(-1)). Partial least squares regression was used to develop predictive models for all measured attributes. Five attributes were successfully modelled with varying degrees of accuracy. The computer vision meltability model allowed for discrimination between high and low melt values (R-2 = 0.64). The hardness and springiness models gave approximate quantitative results (R-2 = 0.77) and the cohesiveness (R-2 = 0.81) and Olson and Price meltability (R-2 = 0.88) models gave good prediction results. (c) 2006 Elsevier Ltd. All rights reserved..

Spectroscopic study and thermal behavior of trivalent lanthanides and yttrium(III) chelates of EDTA using TG-DSC, FTIR, and TG-DSC coupled to FTIR

Solid-state compounds of yttrium and lanthanide chelates of ethylenediaminetetraacetic acid have been synthesized. Simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC), theoretical and experimental infrared spectroscopy (FTIR), elemental analysis, complexometry and TG-DSC coupled to FTIR were used to characterize and to study the thermal decomposition of these compounds. The results provided information about the composition, dehydration, thermal stability, thermal decomposition and identification of gaseous products evolved during the thermal decomposition of these compounds. The theoretical and experimental spectroscopic data suggest the possible modes of coordination of the ligand with the lanthanum and terbium metal ions. © 2013 Akadémiai Kiadó, Budapest, Hungary.

Effect of neutralization and cross-linking on the thermal degradation of chitosan electrospun membranes

Thermal degradation of as electrospun chitosan membranes and samples subsequently treated with ethanol and cross-linked with glutaraldehyde (GA) have been studied by thermogravimetry (TG) coupled with an infrared spectrometer (FTIR). The influence of the electrospinning process and cross-linking in the electrospun chitosan thermal stability was evaluated. Up to three degradation steps were observed in the TG data, corresponding to water dehydration reaction at temperatures below 100 ºC, loss of side groups formed between the amine groups of chitosan and trifluoroacetic acid between 150 – 270 ºC and chitosan thermal degradation that starts around 250 ºC and goes up to 400 ºC. The Kissinger model was employed to evaluate the activation energies of the electrospun membranes during isothermal experiments and revealed that thermal degradation activation energy increases for the samples processed by electrospinning and subsequent neutralization and cross-linking treatments with respect to the neat chitosan powder.

Surface plasmon resonance-coupled photoluminescence and resistive switching behavior of pulsed laser-deposited Ag:SiC nanocermet thin films

In this study, Ag:SiC nanocermets were prepared via rapid thermal annealing (RTA) of pulsed laser-deposited SiC/Ag/SiC trilayers grown on Si substrate. Atomic force microscope images show that silver nanoparticles (Ag NPs) are formed after RTA, and the size of NPs increases with increasing Ag deposition time (t Ag). Sharp dip observed in the reflectance spectra confirmed the existence of Ag surface plasmons (SPs). The infrared transmission spectra showed an intense and broad absorption band around 780–800 cm−1 that can be assigned to Si-C stretching vibration mode. Influence of t Ag on the spectral characteristics of SP-enhanced photoluminescence (PL) and electrical properties of silicon carbide (SiC) films has been investigated. The maximum PL enhancement by 5.5 times for Ag:SiC nanocermets is achieved when t Ag ≈ 50 s. This enhancement is due to the strong resonant coupling between SiC and the SP oscillations of the Ag NPs. Presence of Ag NPs in SiC also induces a forming-free resistive switching with switching ratio of 2 × 10−2. The analysis of I–V curves demonstrates that the trap-controlled space-charge-limited conduction with filamentary model is the governing mechanism for the resistive switching in nanocerment thin films.

Energy transfer mechanism and Auger effect in Er3+ coupled silicon nanoparticle samples

We report a spectroscopic study about the energy transfer mechanism among silicon nanoparticles (Si-np), both amorphous and crystalline, and Er ions in a silicon dioxide matrix. From infrared spectroscopic analysis, we have determined that the physics of the transfer mechanism does not depend on the Si-np nature, finding a fast (< 200 ns) energy transfer in both cases, while the amorphous nanoclusters reveal a larger transfer efficiency than the nanocrystals. Moreover, the detailed spectroscopic results in the visible range here reported are essential to understand the physics behind the sensitization effect, whose knowledge assumes a crucial role to enhance the transfer rate and possibly employing the material in optical amplifier devices. Joining the experimental data, performed with pulsed and continuous-wave excitation, we develop a model in which the internal intraband recombination within Si-np is competitive with the transfer process via an Auger electron"recycling" effect. Posing a different light on some detrimental mechanism such as Auger processes, our findings clearly recast the role of Si-np in the sensitization scheme, where they are able to excite very efficiently ions in close proximity to their surface. (C) 2010 American Institute of Physics.

Far infrared reflectance and optical properties of organic superconductor (TMTSF)2ClO4 /

Polarized reflectance measurements of the quasi I-D charge-transfer salt (TMTSFh CI04 were carried out using a Martin-Puplett-type polarizing interferometer and a 3He refrigerator cryostat, at several temperatures between 0.45 K and 26 K, in the far infrared, in the 10 to 70 cm- 1 frequency range. Bis-tetramethyl-tetraselena-fulvalene perchlorate crystals, grown electrochemically and supplied by K. Behnia, of dimensions 2 to 4 by 0.4 by 0.2 mm, were assembled on a flat surface to form a mosaic of 1.5 by 3 mm. The needle shaped crystals were positioned parallel to each other along their long axis, which is the stacking direction of the planar TMTSF cations, exposing the ab plane face (parallel to which the sheets of CI04 anions are positioned). Reflectance measurements were performed with radiation polarized along the stacking direction in the sample. Measurements were carried out following either a fast (15-20 K per minute) or slow (0.1 K per minute) cooling of the sample. Slow cooling permits the anions to order near 24 K, and the sample is expected to be superconducting below 1.2 K, while fast cooling yields an insulating state at low temperatures. Upon the slow cooling the reflectance shows dependence with temperature and exhibits the 28 cm- 1 feature reported previously [1]. Thermoreflectance for both the 'slow' and 'fast' cooling of the sample calculated relative to the 26 K reflectance data indicates that the reflectance is temperature dependent, for the slow cooling case only. A low frequency edge in the absolute reflectance is assigned an electronic origin given its strong temperature dependence in the relaxed state. We attribute the peak in the absolute reflectance near 30 cm-1 to a phonon coupled to the electronic background. Both the low frequency edge and the 30 cm-1 feature are noted te shift towards higher frequcncy, upon cntering the superconducting state, by an amount of the order of the expected superconducting energy gap. Kramers-Kronig analysis was carried out to determine the optical conductivity for the slowly cooled sample from the measured reflectance. In order to do so the low frequency data was extrapolated to zero frequency using a Hagen-Ru bens behaviour, and the high frequency data was extended with the data of Cao et al. [2], and Kikuchi et al. [3]. The real part of the optical conductivity exhibits an asymmetric peak at 35 cm-1, and its background at lower frequencies seems to be losing spectral weight with lowering of the temperature, leading us to presume that a narrow peak is forming at even lower frequencies.

Overtone Spectra of 1,2-Dichloro-And Dibromo-Ethanes in the Near Infrared Region

The vibrational overtone spectra 0f the liquid phase 1,2-dichloroethane and 1,2-dibromoethane in the spectral regions of CH stretching local mode overtones corresponding to delta v CH= = 2 to delta v CH=5 are reported. The observed spectral features are assigned using the local mode model. LocaI mode frequencies WCH and diagonal local mode anharmonicities XCH are obtained from an analysis of the spectra. The local-local combinations observed are interpreted on the basis of a coupled CH oscillator model hamiltonian. Local-normal combinations show complex structures and their possible assignments are given.

The infrared spectrum of silicon difluoride

The infrared spectrum of the stretching fundamentals of SiF2 has been obtained at a resolution of ≈ 0.1 cm−1 using a FTIR spectrometer. The spectrum has been analysed using computer simulation based on a coupled hamiltonian for v1 and v3, giving v1 = 855.01 cm−1 and v3 = 870.40 cm−1. The relative magnitude and sign of the vibrational transition moments has been determined from the ξC13 Coriolis coupling.

Application of near and mid-infrared spectroscopy to determine cheese quality and authenticity

This paper reviews the current state of development of both near-infrared (NIR) and mid-infrared (MIR) spectroscopic techniques for process monitoring, quality control, and authenticity determination in cheese processing. Infrared spectroscopy has been identified as an ideal process analytical technology tool, and recent publications have demonstrated the potential of both NIR and MIR spectroscopy, coupled with chemometric techniques, for monitoring coagulation, syneresis, and ripening as well as determination of authenticity, composition, sensory, and rheological parameters. Recent research is reviewed and compared on the basis of experimental design, spectroscopic and chemometric methods employed to assess the potential of infrared spectroscopy as a technology for improving process control and quality in cheese manufacture. Emerging research areas for these technologies, such as cheese authenticity and food chain traceability, are also discussed.

The water vapour continuum in near-infrared windows – current understanding and prospects for its inclusion in spectroscopic databases

Spectroscopic catalogues, such as GEISA and HITRAN, do not yet include information on the water vapour continuum that pervades visible, infrared and microwave spectral regions. This is partly because, in some spectral regions, there are rather few laboratory measurements in conditions close to those in the Earth’s atmosphere; hence understanding of the characteristics of the continuum absorption is still emerging. This is particularly so in the near-infrared and visible, where there has been renewed interest and activity in recent years. In this paper we present a critical review focusing on recent laboratory measurements in two near-infrared window regions (centred on 4700 and 6300 cm−1) and include reference to the window centred on 2600 cm−1 where more measurements have been reported. The rather few available measurements, have used Fourier transform spectroscopy (FTS), cavity ring down spectroscopy, optical-feedback – cavity enhanced laser spectroscopy and, in very narrow regions, calorimetric interferometry. These systems have different advantages and disadvantages. Fourier Transform Spectroscopy can measure the continuum across both these and neighbouring windows; by contrast, the cavity laser techniques are limited to fewer wavenumbers, but have a much higher inherent sensitivity. The available results present a diverse view of the characteristics of continuum absorption, with differences in continuum strength exceeding a factor of 10 in the cores of these windows. In individual windows, the temperature dependence of the water vapour self-continuum differs significantly in the few sets of measurements that allow an analysis. The available data also indicate that the temperature dependence differs significantly between different near-infrared windows. These pioneering measurements provide an impetus for further measurements. Improvements and/or extensions in existing techniques would aid progress to a full characterisation of the continuum – as an example, we report pilot measurements of the water vapour self-continuum using a supercontinuum laser source coupled to an FTS. Such improvements, as well as additional measurements and analyses in other laboratories, would enable the inclusion of the water vapour continuum in future spectroscopic databases, and therefore allow for a more reliable forward modelling of the radiative properties of the atmosphere. It would also allow a more confident assessment of different theoretical descriptions of the underlying cause or causes of continuum absorption.

Peat as a natural solid-phase for copper preconcentration and determination in a multicommuted flow system coupled to flame atomic absorption spectrometry

The physical and chemical characteristics of peat were assessed through measurement of pH, percentage of organic matter, cationic exchange capacity (CEC), elemental analysis, infrared spectroscopy and quantitative analysis of metals by ICP OES. Despite the material showed to be very acid in view of the percentage of organic matter, its CEC was significant, showing potential for retention of metal ions. This characteristic was exploited by coupling a peat mini-column to a flow system based on the multicommutation approach for the in-line copper concentration prior to flame atomic absorption spectrometric determination. Cu(II) ions were adsorbed at pH 4.5 and eluted with 0.50 mol L(-1) HNO(3). The influence of chemical and hydrodynamic parameters, such as sample pH, buffer concentration, eluent type and concentration, sample flow-rate and preconcentration time were investigated. Under the optimized conditions, a linear response was observed between 16 and 100 mu g L(-1), with a detection limit estimated as 3 mu g L(-1) at the 99.7% confidence level and an enrichment factor of 16. The relative standard deviation was estimated as 3.3% (n = 20). The mini-column was used for at least 100 sampling cycles without significant variation in the analytical response. Recoveries from copper spiked to lake water or groundwater as well as concentrates used in hemodialysis were in the 97.3-111 % range. The results obtained for copper determination in these samples agreed with those achieved by graphite furnace atomic absorption spectrometry (GFAAS) at the 95% confidence level. (C) 2009 Elsevier B.V. All rights reserved.