Isabel C. Neves

Acylation of phenol with acetic acid over a HZSM5 zeolite, reaction scheme

Abstract The scheme of the gas phase phenol acylation with acetic acid on a HZSM5 zeolite was established from the effect of contact time (hence of conversion) on the product distribution. Phenyl acetate and o -hydroxyacetophenone are primary products, O-acylation being much faster than C-acylation. At high conversion, part of the o -hydroxyacetophenone results from the acylation of phenol with phenyl acetate. The formation of p -hydroxyacetophenone which does not occur through phenol acylation involves the hydrolysis of p -acetoxyacetophenone selectively formed through the autoacylation of phenyl acetate. The ortho -selectivity of phenol acylation can be related to a pronounced stabilization of the transition state while the para -selectivity of phenyl acetate autoacylation could be due to a steric hindrance to the approach of the acetyl group in the ortho -position of phenyl acetate.

Potentiation of 5-fluorouracil encapsulated in zeolites as drug delivery systems for in vitro models of colorectal carcinoma

The studies of potentiation of 5-fluorouracil (5-FU), a traditional drug used in the treatment of several cancers, including colorectal (CRC), were carried out with zeolites Faujasite in the sodium form, with different particle sizes (NaY, 700nm and nanoNaY, 150nm) and Linde type L in the potassium form (LTL) with a particle size of 80nm. 5-FU was loaded into zeolites by liquid-phase adsorption. Characterization by spectroscopic techniques (FTIR, (1)H NMR and (13)C and (27)Al solid-state MAS NMR), chemical analysis, thermal analysis (TGA), nitrogen adsorption isotherms and scanning electron microscopy (SEM), demonstrated the successful loading of 5-FU into the zeolite hosts. In vitro drug release studies (PBS buffer pH 7.4, 37°C) revealed the release of 80-90% of 5-FU in the first 10min. To ascertain the drug release kinetics, the release profiles were fitted to zero-order, first-order, Higuchi, Hixson-Crowell, Korsmeyer-Peppas and Weibull kinetic models. The in vitro dissolution from the drug delivery systems (DDS) was explained by the Weibull model. The DDS efficacy was evaluated using two human colorectal carcinoma cell lines, HCT-15 and RKO. Unloaded zeolites presented no toxicity to both cancer cells, while all DDS allowed an important potentiation of the 5-FU effect on the cell viability. Immunofluorescence studies provided evidence for zeolite-cell internalization.

Zeolite-encapsulated copper (II) complexes with N3O2 Schiff bases: synthesis and characterization

Abstract Copper(II) complexes with N 3 O 2 Schiff base ligands[B: bis-(acetylacetone)-3-amino-bis(propylenediimine) = H 2 (acac) 2 trien; C: bis-(acetylacetone)-3-methylamino-bis(propylenediimine) = H 2 (acac) 2 Metrien] were encapsulated in the supercages of zeolite Y in a two-step process: (i) adsorption of copper(II) acetylacetonate in the supercage of the zeolite; (ii) in-situ Schiff base condensation of the copper(II) acetylacetonate complex with corresponding triamine. The resulting materials were purified by Soxhlet extraction. Bulk and surface chemical analysis, surface characterization (SEM, XPS), spectroscopic characterization (UV/Vis, FTIR), electron paramagnetic resonance and temperature-programmed desorption studies of the new materials provide evidence for the entrapment of Cu(II) complexes in the zeolite supercages.

Phenol acylation: unexpected improvement of the selectivity to o-hydroxyacetophenone by passivation of the external acid sites of HZSM5

The acylation of phenol by acetic acid on zeolite ZSM5 is unexpectedly oriented towards o-hydroxyacetophenone by dealumination of the outer surface of the crystallites, which can be ascribed to the existence of two different pathways for the formation of o- and p-hydroxyacetophenones.

Reutilization of Cr-Y zeolite obtained by biosorption in the catalytic oxidation of volatile organic compounds

This work aims at the reutilization of a Cr-loaded NaY zeolite obtained by biorecovery of chromium from water as catalyst in the oxidation of volatile organic compounds (VOC). Cr-NaY catalysts were obtained after biosorption of Cr(VI) using a bacterium, Arthrobacter viscosus, supported on the zeolite. The biosorption experiments were conducted at different pH values in the range 1-4. The catalysts were characterized by several techniques, namely ICP-AES, SEM-EDS, XRD, XPS, Raman, H(2)-TPR and N(2) adsorption. The zeolite obtained at pH 4 has the highest content of chromium, 0.9%, and was selected as the best catalyst for the oxidation of different VOC, namely ethyl acetate, ethanol and toluene. For all VOC tested, the catalyst with chromium showed higher activity and selectivity to CO(2), in comparison with the starting zeolite NaY. The presence of chromium shifted also the reaction pathways. In terms of selectivity to CO(2), the following sequence was observed: ethyl acetate>toluene>ethanol.

Mechanism of Phenylacetate Transformation on Zeolites

Summary The transformation of phenylacetate was carried out over two zeolites: HY (Si/Al = 20) and HZSM5 (Si/Al = 40) at 400°C under atmospheric pressure. The reactivities of the products and intermediates were also studied under the same conditions. On both catalysts the main product was phenol which means that ketene was also formed. HY led mainly to ortho-hydroxyacetophenone while HZSM5 gave both ortho- and para-hydroxyacetophenones in equal amounts. 2-Methylchromone and 4-methylcoumarine were formed on HY only and supposedly resulted from an intramolecular condensation of ortho-acetoxyacetophenone which was not observed among the products. On HZSM5 dehydroacetic acid and 4-acetoxy 6-methyl 2-pyrone were formed presumably through autocondensation of ketene. Para-acetoxyacetophenone was observed on both catalysts. Water had practically no effect on the activity and selectivity of HY while it increased the stability of HZSM5 markedly.

Highly efficient reduction of bromate to bromide over mono and bimetallic ZSM5 catalysts

The reduction of bromate to bromide was successfully catalyzed by mono and bimetallic catalysts based on ZSM5 zeolites. This reaction is important since the presence of bromate in water is potentially carcinogenic to humans. The catalysts were prepared by ion-exchange and incipient wetness methods with different metals (copper, palladium, rhodium and thorium) using ZSM5. Several analytical techniques (N2 adsorption, TPR experiments, NH3-TPD, FTIR, XRD, SEM/EDX and TEM/EDX) were used to characterize the mono and bimetallic catalysts prepared by the two methods. The catalytic tests were carried out in a semi-batch reactor under hydrogen, working at room temperature and pressure. All catalysts prepared are undeniably effective in achieving the complete conversion of bromate into bromide. The most promising among the catalysts tested in this work are the palladium bimetallic catalysts.

Host(beta zeolite)–guest (copper(II)–methyladenine complex) nanomaterials: synthesis and characterization

The guest copper(II)–methyladenine complex was entrapped into beta zeolite (BEA) as a host by a process of sequential introduction of the components in the liquid phase followed by assembly inside the void space of the zeolite. The beta zeolite was prepared by an original technique. The appropriate process chosen for the in situ complex synthesis was using a 9-methyladenine ligand : copper(II) molar ratio of 4 : 1. The new host–guest nanomaterial was purified by Soxhlet extraction. The BEA zeolite with copper(II)–methyladenine complex was characterized by several techniques: SEM and XRD, chemical analysis (CA), spectroscopic methods (EPR, FTIR, UV-Vis and XPS) and TGA (thermal analysis). Analysis of the data indicates that the guest copper(II) complex was effectively immobilized in BEA without any modification of the morphology and structure of the zeolite. The coordination of the 9-methyladenine ligand with copper(II) ion as guest in the host nanomaterial was obtained with a preferential 1 : 1 stoichiometry.

Iron and Chromium Removal from Binary Solutions of Fe(III)/Cr(III) and Fe(III)/Cr(VI) by Biosorbents Supported on Zeolites

The removal of metallic ions from binary aqueous solutions of Fe(III)/Cr(III) and Fe(III)/Cr(VI) by an Arthrobacter viscosus biofilm supported on NaY zeolite was investigated. Experiments were repeated with suspended biomass for comparison purposes. Batch assays were performed using different concentrations (10, 25 and 40 mg/L), for both metals in solution. Results indicated that Arthrobacter viscosus is able to retain the metallic ions, although not totally. The removal efficiencies were improved when the biofilm was supported on the zeolite, for all the initial concentrations of Cr(III), for the intermediate and higher concentration of Cr(VI) and for all range of initial concentrations of Fe(III), in the presence of Cr(III). The bacteria reduce Cr(VI) to Cr(III) and, only then, this cation may be entrapped in the framework zeolite by ion exchange. Suspended bacteria had higher affinity for Fe(III), than for Cr(VI) or Cr(III), while the conjugated system was selective to Fe(III) when in the presence of Cr(VI). For solutions of Fe(III)/Cr(III), very high removals were achieved by the supported system, ranging from 94 to 100 % for Cr(III) and from 98 to 100 % for Fe(III). The conjugated system also reached the highest removal ratio of Cr(VI), 36 %, for the initial concentration of 40 mg/L. The materials in study were characterized by techniques such as FTIR, SEM and chemical analyses.

Comparative study between natural and artificial zeolites as supports for biosorption systems

This study aims the definition of a new material that may act as a robust and yet cost effective biosorbent for treatment of wastewater with low concentration of heavy metals. A comparative study was made between two biosorption systems composed of an Arthrobacter viscosus biofilm supported on Cuban natural zeolites and on prepared NaY and NaX, in terms of their ability to retain ionic chromium. The bacterium is able to reduce Cr(VI) to Cr(III) and, only then, this smaller and positive ion may be entrapped in the zeolite cages by ion exchange. The first support was tested in a continuous flow semi-packed bed column. The highest removal ratio, 42%, was achieved for initial chromium concentration of 10 mg/L, but the best up-take, 5.5 mg/gzeolite, was obtained for initial concentration of 70 mg/L. Biosorbents prepared with the same biofilm supported in NaY and NaX zeolites were also considered in batch studies, with a typical kinetics of biosorption processes, reaching 20% of initial chromium removal within an initial range of Cr(VI) concentration between 50 and 250 mg/L. These last structures were characterized by spectroscopic methods (FTIR and ICP-AES), surface analysis (DRX) and thermal analysis (TGA). All these techniques indicated that the biosorption process does not modify the morphology and structure of the FAU-zeolites.