Photoluminescence study of terbium-exchanged ultrastable Y zeolites: number of species, photoluminescence decays, and decay-associated spectra

Terbium-exchanged ultrastable Y (USY) zeolites were investigated by using time-resolved photoluminescence spectroscopy techniques and methods. To determine the distribution of terbium species in USY zeolites together with their photoluminescence properties, several analysis methods for the time-resolved luminescence spectra were used such as the area normalization of time-resolved photoluminescence spectra, singular value decomposition, global nonlinear least squares, and the maximum entropy. Except for a questionable long lifetime, small contribution of a terbium species with lifetime of 1.9¿2.1 ms, all the experimental and analysis results converged to a two terbium species distribution with lifetimes varying between 410¿440 and 1000¿1100 μ s . The effects of the silylation of terbium-exchanged USY zeolites with phenyl-, vinyl-, and hexadecyltrimethoxysilanes on the lanthanide¿s photoluminescence properties were also described

Robust Bayes-Like Estimation: Rho-Bayes estimation

We consider the problem of estimating the joint distribution $P$ of $n$ independent random variables within the Bayes paradigm from a non-asymptotic point of view. Assuming that $P$ admits some density $s$ with respect to a given reference measure, we consider a density model $\overline S$ for $s$ that we endow with a prior distribution $\pi$ (with support $\overline S$) and we build a robust alternative to the classical Bayes posterior distribution which possesses similar concentration properties around $s$ whenever it belongs to the model $\overline S$. Furthermore, in density estimation, the Hellinger distance between the classical and the robust posterior distributions tends to 0, as the number of observations tends to infinity, under suitable assumptions on the model and the prior, provided that the model $\overline S$ contains the true density $s$. However, unlike what happens with the classical Bayes posterior distribution, we show that the concentration properties of this new posterior distribution are still preserved in the case of a misspecification of the model, that is when $s$ does not belong to $\overline S$ but is close enough to it with respect to the Hellinger distance.Comment: 68 page

Graphenes as Metal-Free Catalysts with Engineered Active Sites

[EN] This Perspective article highlights how recent discoveries on the activity of defective graphene to promote different organic reactions as metal-free catalysts has led to propose certain substructures present on these defective graphenes as active sites. The sustainability of using as catalysts graphenes obtained from biomass and the possibility to generate active sites by introducing defects on the sheet are the two main characteristics triggering research in this area. Emphasis is made in the need to gain understanding on the nature of the active sites and how this understanding requires the combination of conventional kinetic experiments as well as advanced characterization tools. The relationship between catalysis by graphene and that by organocatalysis has also been remarked.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa, Grapas, and CTQ2015-69153-CO2-1) and Generalitat Valenciana (Prometo 2013-014) is gratefully acknowledged. A.P. also thanks the Spanish Ministry of Economy and Competitiveness for a Ramon y Cajal research associate contract.Primo Arnau, AM.; Parvulescu, V.; García Gómez, H. (2017). Graphenes as Metal-Free Catalysts with Engineered Active Sites. The Journal of Physical Chemistry Letters. 8(1):264-278. https://doi.org/10.1021/acs.jpclett.6b01996S2642788

Pervaporation of Aqueous Ethanol Solutions Through Pure and Composite Cellulose Membranes

A procedure for synthesis of pure and composite membranes based on cellulose dissolved in NaOH-urea/ thiourea solutions was developed. The phase inversion method was employed for cellulose solution conversion to supported and non-supported membranes. The use of tetraethyl orthosilicate (TEOS) as precursor in synthesis of composite cellulose membranes produced significant changes in their structure and pervaporation behaviour. The obtained membranes were tested for the pervaporation of ethanol-water system. Pervaporation performances, which were evaluated in terms of total permeate flux, separation factor and pervaporation separation index, strongly depended on TEOS loading, ethanol concentration and operation temperature

Application of the Nanofiltration Process for Concentration of Polyphenolic Compounds from Geranium robertianum and Salvia officinalis Extracts

The aim of this study was to prove the efficiency of the nanofiltration process for the concentration of polyphenolic compounds from Geranium robertianum and Salvia officinalis extracts and to evaluate the extract’s antioxidant activity. A lab-scale cross-flow set-up using flat-sheet configuration membrane was employed for all experiments. Two nanofiltration membranes have been used: SelRO MPF-36 (Koch membrane) and an organic-inorganic membrane (polysulfone with SBA-15-NH2). When the organic-inorganic membranes were used in the nanofiltration process, the obtained concentrated extracts proved to have higher polyphenol and flavonoid rejections, in both cases (Geranium robertianum and Salvia officinalis). The obtained values were over 88 % DPPH inhibition, for concentrated extracts, using the DPPH method. The concentrated extracts obtained after nanofiltration NF2 (organic-inorganic membrane) had the strongest scavenging activity for all extracts and almost completely inhibited DPPH absorption (92.9 % for Geranium robertianum concentrated extract and 90.1 % for Salvia officinalis concentrated extract). These features turn the studied, concentrated extracts into a good source for further medicinal applications

The kinetics and mechanism of the organo-iridium catalysed racemisation of amines

The dimeric iodo-iridium complex [IrCp*I2 ]2 (Cp*=pentamethylcyclopentadiene) is an efficient catalyst for the racemisation of secondary and tertiary amines at ambient and higher temperatures with a low catalyst loading. The racemisation occurs with pseudo-first-order kinetics and the orresponding four rate constants were obtained by monitoring the time dependence of the concentrations of the (R) and (S) enantiomers starting with either pure (R) or (S) and show a first-order dependence on catalyst concentration. Low temperature 1H NMR data is consistent with the formation of a 1:1 complex with the amine coordinated to the iridium and with both iodide anions still bound to the metal-ion, but at the higher temperatures used for kinetic studies binding is weak and so no saturation zero-order kinetics are observed. A cross-over experiment with isotopically labelled amines demonstrates the intermediate formation of an imine which can dissociate from the iridium complex. Replacing the iodides in the catalyst by other ligands or having an amide substituent in Cp* results in a much less effective catalysts for the racemisation of amines. The rate constants for a deuterated amine yield a significant primary kinetic isotope effect kH/kD = 3.24 ndicating that hydride transfer is involved in the rate-limiting step

Integrated System of Fed Batch ABE Biosynthesis and Solvent Recovery by Pervaporation

Anaerobic fermentation of glucose substrate by Clostridium acetobutylicum bacteria at 34-39 °C produces butanol, acetone, and ethanol solvents as metabolites. In the case of batch and fed batch bioreactors, the control of butanol concentration in the fermentation broth is recommended for diminishing its inhibitory effect on the bacterial system. Solvent recovery from batch or fed batch bioreactors by using an ultrafiltrationpervaporation system could be an efficient solution to improve the process performances. A mathematical model was developed in order to describe the dynamics of solvent production in an integrated system of fed batch fermentation and solvent recovery. Simulations performed under various operating conditions were used for optimizing the biosynthesis process, i.e., for maximizing the solvent production and minimizing the substrate concentration in the fermentation medium. Initial substrate concentration in the bioreactor, feed flow rate, feed substrate concentration, starting time of feed and ultrafiltration-pervaporation, surface area of ultrafiltration and pervaporation units were selected as process control variables

Improved performance of non-thermal plasma reactor during decomposition of trichloroethylene: Optimization of the reactor geometry and introduction of catalytic electrode

The decomposition of trichloroethylene ITCE) by non-thermal plasma was investigated in a dielectric barrier discharge (DBD) reactor with a copper rod inner electrode and compared with a plasma-catalytic reactor. The particularity of the plasma-catalytic reactor is the inner electrode made of sintered metal fibers (SMF) coated by transition metal oxides. In order to optimize the geometry of the plasma reactor, the efficiency of TCE removal was compared for different discharge gap lengths in the range of 1-5 mm. Shorter gap lengths (1-3 mm) appear to be more advantageous with respect to TCE conversion. In this case TCE conversion varies between 67% and 100% for input energy densities in the range of 80-480 J/l, while for the 5 turn discharge gap the conversion was lower (53-97%) for similar values of the input energy. As a result of TICE oxidation carbon monoxide and carbon dioxide were detected in the effluent gas. Their selectivity was rather low, in the range 14-24% for CO2 and 11-23% for CO, and was not influenced by the gap length. Several other chlorinated organic compounds were detected as reaction products. When using MnOx/SMF catalysts as the inner electrode of the DBD reactor, the TCE conversion was significantly enhanced, reaching similar to 95% at 150 J/l input energy. The selectivity to CO2 showed a major increase as compared to the case without catalysts, reaching 58% for input energies above 550 J/l. (C) 2007 Elsevier B.V. All rights reserved