Thermal decomposition of lignocellulosic materials: comparison of the results obtained in different experimental systems

An experimental system that allows the use of large particle sizes and the simulation of different operating conditions was built to study the thermal decomposition of lignocellulosic materials. The values of solid conversion and of temperature obtained at different points using spherical particles of pine wood 2 cm in diameter are shown. The conversion values are compared with those calculated from the equations obtained in a thermobalance for small particle sizes.     

Preparation of USY zeolite VOx supported catalysts from V(AcAc)3 and NH4VO3. Catalytic properties for the dehydrogenation of n-butane in oxygen-free atmosphere

The preparation of different samples of vanadia supported on ultrastable zeolite (VO(x)/USY) is discussed. The samples were prepared in order to obtain highly dispersed V-species, avoiding the formation of crystalline vanadia and the destruction of the zeolite framework. Two methods were employed for preparing VO(x)/USY samples: an organic route using V(AcAc)3 and an inorganic route using NH4VO3. The characterization of the samples was performed with XRD, TPR, NH3-TPD, and N2 isotherms. From these results it is concluded that when VO(x) is supported on the surface of USY from acidic aqueous solution of ammonium metavanadate, the destruction of the zeolite framework is accomplished. For higher pH values in the impregnating solution, undesired V2O5 is formed on the USY surface. On the other hand, VO(x)/USY prepared from the organic precursor shows no destruction of the USY structure. In addition, highly dispersed VO(x) are formed, though for relatively high V loadings (6%) an obstruction of the zeolite windows takes place. The samples are tested as catalysts for gas phase dehydrogenation of n-butane to olefins. The catalysts prepared from NH4VO3 are almost inactive for the reaction. On the other hand, both samples prepared from V(AcAc)3 present initial conversion levels in the 8-12% range. However, the selectivity depends on the V loading, the catalysts with 6% loading being the most selective (75%). The catalytic patterns of the samples (activity and selectivity) are in agreement with the physicochemical features of the VO(x)/USY surface.     

Infrared Study of Solid Dispersions of β-Cyclodextrin with Naphthalene Derivitaves

The inclusion complexes of β-cyclodextrin (β-CD) with naphthalene and some of its derivatives in the solid state have been studied by infrared spectroscopy. Digital subtraction, deconvolution and curve fitting have been used to investigate the interactions between the naphthalene derivatives andβ-CD. Several preparation methods for the solid dispersions have been tested, using FTIR as an effective tool to evaluate the interactions at the molecular level. The effects of temperature and humidity on the spectra have been also analyzed. A carbonyl moiety in the guest molecule can increase the stability of the complex by establishing specific interactions with the hydroxyl groups of the CD cavity rims. The stability of the complexes is higher for 2-naphthylacetate than that for 1-naphthyl acetate, andso is the degree of association of its carbonyl groups. On the other hand, 2-acetylnaphthaleneforms very stable inclusioncomplexes although its carbonyl groups appear to be significantly less associated.     

Intermolecular proton transfer in solid phase: a rare example of crystal-to-crystal transformation from hydroxo- to oxo-bridged iron(III) molecule-based magnet

Intermolecular proton transfer in solid phase from the hydroxo bridge to a water molecule occurs in a new mu-hydroxo iron(III) compound of formula {EtNH3[Fe2(ox)2Cl2(mu-OH)].2H2O}n leading to a still crystalline compound in which the mu-oxo bridge replaces the mu-hydroxo one. Both three-dimensional compounds exhibit magnetic ordering at Tc ca. 70 K due to a spin canting.     

Hydrogen sulphide doping of GaAs and AlxGa1−xAs grown by molecular beam epitaxy (MBE)

H₂S gas has been used during molecular beam epitaxy (MBE) growth of GaAs and Al _x Ga_1–x As as sulphur vector forn-type doping. Doping efficiencies are less than 10^–3 at usual growth temperatures, and are limited by an incorporation competitive surface process, probably 2Ga+H₂SGa₂S+H₂. In Al_xGa_1–x As forx0.2 the doping efficiency is further reduced by carrier freeze-out at deep levels. Measured thermal activation energies depend on growth conditions and remain relatively low even up to the direct-indirect bandgap crossover for substrate temperatures in the 585–645 C range.     

Quality control of Metamitron in agrochemicals using Fourier transform infrared spectroscopy in the middle and near range

Two vibrational spectrometry-based methodologies were developed for Metamitron determination in pesticide formulations. Fourier transform-middle infrared (FT-MIR) procedure was based on the extraction of Metamitron by CHCl₃ and latter determination by peak area measurement between 1556 and 1533 cm⁻¹, corrected with a two points baseline established from 1572 to 1514 cm⁻¹. Fourier transform-near infrared (FT-NIR) determination was made after the extraction of Metamitron in acetonitrile and measuring the peak area between 6434 and 6394 cm⁻¹ corrected using a two points baseline defined between 6555 and 6228 cm⁻¹. Repeatability, as relative standard deviation, of 5 independent measurements at mg g⁻¹ concentration level, of 0.16% and 0.07% for MIR and NIR and a limit of detection of 0.03 and 0.004 mg g⁻¹ were obtained for MIR and NIR, respectively.NIR determination provides a sample frequency of 120 h⁻¹, higher than that found by MIR and liquid chromatographic methods (60 and 15 h⁻¹, respectively). On the other hand, the NIR method reduces the solvent consumption and waste generation, to only 1 ml acetonitrile per sample as compared with 3.4 ml chloroform required for the MIR determination and 60 ml acetonitrile used in the chromatographic reference procedure. So, vibrational procedures can be considered serious alternatives to long and time consuming chromatographic methods usually recommended for quality control of commercially available pesticide formulations.     

A trinickel dipyridylamido complex with metal-metal bonding interaction: prelude to polynickel molecular wires and devices?

The molecule Ni(3)(dpa)(4)Cl(2) (1) can be oxidized by AgPF(6) to give crystalline Ni(3)(dpa)(4)(PF(6))(3) (2) (dpa is the anion of di(2-pyridyl)amine). This reversible oxidation occurs at a potential of 0.908 V vs Ag/AgCl electrochemically. The X-ray structure of 2 shows that the oxidation causes a major structural change (even though it is reversible), namely, a contraction of the Ni-Ni distances from ca. 2.43 A to 2.284[1] A. In addition, the electronic structure changes so that from four unpaired electrons in 1 there is only one in 2. From these remarkable results, it is inferred that while 1, and all higher homologues with 5, 7, 9,... nickel atoms are poor electronic conductors, the cations obtainable from them may be much better ones. This in turn means that by controlling the oxidation state electrochemically, these molecules may be able to function as nanoscale diodes.     

Cyclopentathiadiazines, new heterocyclic materials from cyclic enaminonitriles

Indene and cyclopentene enaminonitriles were reacted with SCl2, iBu3N and NCS to give the first cyclopenta[1,2,6]thiadiazines that showed unusual characteristics, one as a NIR dye and another as a liquid crystal.     

Dynamic contact angle and spreading rate measurements for the characterization of the effect of dentin surface treatments

A new methodology capable of providing reliable and reproducible contact angle (theta) data has been employed to study the effect of clinical treatments grinding, acid etching, and deproteinization on medial dentin tissue. It is based on the application of the ADSA-CD algorithm to the determination of low-rate dynamic contact angles, obtained from slowly growing drops, and on contact angle measurement, as well as spreading behavior analysis, during the relaxation of the system (water on treated dentin) after initial drop growth. The theta data obtained were substantially more reproducible than those obtained with classical methods. A net effect of the treatment on theta was found, increasing dentin wettability: theta (polished) >theta (etched) >theta (deproteinized). The spreading rates correlate with the angles and are adequate for the dentin surface characterization. ANOVA and SNK tests show that for advancing contact angles the means corresponding to all treatments are significantly different. In the relaxing phase, mean angle and spreading rates on polished dentin differ significantly from those on etched and deproteinized dentin, but the latter do not differ significantly from each other.