Zeolites are ordered crystalline materials with a promising performance for a wide range of applications such as catalysis, petrochemistry, environmental remediation, and medicine, but have scarcely been evaluated in Analytical Chemistry. Their unique and fascinating properties such as their high surface area, high adsorption capacity and molecular selectivity, chemical and thermal stability, ion-exchange capacity, low cost extraction and synthesis, and their easy modification, which provides a wide range of zeolite-based materials, make zeolites potential sorbents for extraction procedures. Therefore, in this review, we provide an overview of the current status of zeolites and zeolite-based materials used in extraction and microextraction techniques with reference to recent applications and highlight some of the novel advances. ; The authors would like to thank the Spanish Ministry of Economy and Competitiveness and European Union (FEDER funds) (project no. CTQ2016-79991-R) for financial support. P. Baile also thanks the Ministry of Education, Culture and Sports for her FPU grant (FPU14/04589).
In recent years, secondary batteries received considerable attention as promising technology for energy storage in combination with renewable energy sources. The oxidation of carbon in conventional air electrodes reduces the life of secondary batteries. One possible solution for overcoming this problem is the replacement of carbon material with zeolite.Zeolite is a natural or synthetic porous material with crystalline structure which provides the necessary gas permeability. The required hydrophobicity of the electrode is ensured by mixing zeolite with an appropriate amount of polytetrafluoroethylene following a specially developed procedure. The main purpose of the present research is to discover the optimum level of hydrophobicity (impregnation) of zeolite. Moreover, appropriate amount of PTFE will ensure better mechanical stability and long charge/discharge cycle life.The results from this study show that the replacement of carbon with zeolite in the gas diffusion layer is a promising direction for optimization of the bi-functional air electrode. The relationship between the particle size and the hydrophobicity of the electrode was found. It was found that the mechanical stability and hydrophobicity of the electrode improved with the replacement of the emulsion powder. The gas permeability is maintained in the norms, which guarantees the good performance of the electrode. More than 200 charge/discharge cycles were reached.
Diesel vehicles are widely used for transportation of people and goods, which is responsible for a significant consumption of diesel, and the associated release of mainly CO 2 , but also pollutantssuch as CO, hydrocarbons, soot particles and NO x (x = 1,2). These pollutants threat the health of humans and negatively affect the environment, and therefore, abatement is enforced by legislation, which is practically handled by installation of exhaust after treatment systems in passenger cars aswell as in heavy-duty vehicles. A crucial component of the after treatment systems is the catalystfor selective catalytic reduction of NO x with NH 3 (NH 3 -SCR). Current state-of-the-art SCR catalysts are zeolite-based Cu-CHA materials, which is mainly due to their unmatched low temperature activity. Unfortunately, the presence of 0.5-2 ppmv of SO 2 in diesel exhaust significantly inhibits the low-temperature activity Cu-CHA catalysts, which diminishes the NO x removal efficiency. In order to comply with current and future NOx emission limits, development of more SO 2 resistant Cu-CHA catalyst systems is necessary, which requires a better fundamental understanding of the deactivation of Cu-CHA catalysts by SO 2 . In this work, Cu-CHA catalysts have been produced and exposed to SO 2 in various gas mixtures at different temperatures (200-550 °C), and exposure times, to investigate the effects of SO2 at the various conditions of an after treatment system. The uptake of S, determined from elemental analysis and adsorption/desorption measurements, has been compared to the impact on the catalytic performance in the NH3-SCR reaction after the different SO 2 exposures, and after regeneration at 550 °C in SO 2 -free gas. In parallel, characterization with scanning transmissionelectron microscopy – energy dispersive X-ray (STEM-EDX) spectroscopy and electron paramagnetic resonance (EPR) spectroscopy have been used to assess the location of S, and densityfunctional theory (DFT) calculations have been carried out to determine possible Cu,S species. The deactivation is established to be the result of formation of Cu,S species, and not a consequence of ammonium sulfate precipitation, since the S/Cu ratio has not been observed to significantly exceed 1. Some Cu,S species decompose below 550 °C (reversible), while a more stable Cu sulfate species (irreversible) that decomposes around 650 °C, can form on a restricted fraction of the Cu. Formation of the different Cu,S species is dependent on several conditions such as the oxidation state of Cu, the temperature, and the presence of H 2 O and SO 3 . DFT calculations suggested that SO 2 adsorbs more stably on CuI, while SO 3 preferably reacts with CuII, which was consistent with experimental data. At 200 °C it was observed that the formation of Cu,S species is enhanced by co-feeding SO 3 , whereas at 550 °C there is no measurable impact. In the same experiments, the presence of H 2 O enhanced the formation of irreversible Cu sulfate at both 200 and 550 °C, but had no impact on the formation of reversible Cu,S species. While there is no apparent impact of the chemical composition of the CHA framework (H n Al n Si1-nO 2 vs H n SinAlP1- n O 4 ), the CuII sites associated with one or two framework Al centers, Z-CuO Hand Z2-Cu, respectively, have different resistance towards SO 2 , as indicated by DFT calculations.The EPR characterization indirectly showed that mainly Z-CuOH reacts with SO x to formation of the reversible Cu,S species, whereas certain Z2-Cu sites were directly seen to participate in the formation of irreversible Cu sulfate. Finally, other Z2-Cu sites were inert to SO 2 exposure, whichexplains why a 100% deactivation has not been observed. In terms of the impact of reversible and irreversible Cu,S species on the NH3-SCR activity, the deactivation inferred by the reversible Cu,S species was always disproportionately larger than theS/Cu ratio, and caused a lowering of the apparent SCR activation energy with increasing S/Curatio. In contrast, the remaining irreversible Cu,S species after regeneration exhibited a 1:1correlation between the deactivation and S/Cu ratio, as well as the apparent activation energieswere restored to the same level as the fresh catalyst. The deactivation occurs by exposure to 1.5ppmv SO 2 , and by increasing the SO 2 concentration and simultaneously decreasing the exposuretime correspondingly, similar deactivation levels are reached. Hence, it appears to depend on theproduct of the SO2 concentration and exposure time. Accelerated SO2 exposures showed that the deactivation occurs fast, reaching at least 80% before 5% of the lifetime SO 2 exposure. However, the deactivation could at all times be lowered to about 20%, which is probably dependent on thespecific Cu-CHA catalyst. Thus, the application of Cu-CHA catalysts in aftertreatment systems iscontingent on regeneration. A new method to quantify the active amount of Cu in Cu-CHA catalysts by measuring the NO consumption during a temperature-programmed reduction in NO+NH 3 has been developed (NOTPR). The method is applicable on regenerated catalysts, and potentially also on SO 2 exposed catalysts.
[EN] Delaminated and pillared zeolites are an innovative family of molecular sieves which introduced a different concept inside the synthesis of active catalysts or inorganic supports. These types of materials exhibit an elevated accessibility due to their open structure, characterized by the high external surface area without imposed restrictions controlled by the pore sizes. These open zeolites are conformed by crystalline ordered (pillared zeolites) or disordered (delaminated zeolites) individual layers, exhibiting textural properties which are favorable to carry out catalytic processes in which it is necessary to employ catalysts with completely accessible active sites. The elevated external surface area of these zeolites is profitable to generate more specific organic-inorganic materials, acting in this case as stable inorganic matrixes. The preparation of this open type-zeolites family is based on the modification of, previously synthesized, zeolitic precursors which are preexpanded to obtain the final delaminated or pillared zeolites which exhibit very different physicochemical properties compared with the starting precursors. Along this paper, the most relevantMWW-type high accessible zeoliticmaterials will be considered. Their nature, characteristics, and reactivity will be shown in the function of the employed synthesis method for their preparation and the postsynthesis treatments carried out, tuning their properties. ; The author thanks the Spanish Government (Consolider Ingenio 2010-MULTICAT (CSD2009–00050) and MAT2011–29020-C02-01) for the financial support. ; Díaz Morales, UM. (2012). Layered Materials with Catalytic Applications: Pillared andDelaminated Zeolites from MWW Precursors. ISRN Chemical Engineering. 2012(ID 537164):1-35. https://doi.org/10.5402/2012/537164 ; S ; 1 ; 35 ; 2012 ; ID 537164
Catalytic oxidation is a key technology for the conversion of petroleum-based feedstocks into useful chemicals (e.g., adipic acid, caprolactam, glycols, acrylates, and vinyl acetate) since this chemical transformation is always involved in synthesis processes. Millions of tons of these compounds are annually produced worldwide and find applications in all areas of chemical industries, ranging from pharmaceutical to large-scale commodities. The traditional industrial methods to produce large amounts of those compounds involve over-stoichiometric quantities of toxic inorganic reactants and homogeneous catalysts that operate at high temperature, originating large amounts of effluents, often leading to expensive downstream processes, along with nonrecovery of valuable catalysts that are loss within the reactant effluent. Due to the increasingly stringent environmental legislation nowadays, there is considerable pressure to replace these antiquate technologies, focusing on heterogeneous catalysts that can operate under mild reactions conditions, easily recovered, and reused. Parallelly, recent advances in the synthesis and characterization of metal complexes and metal clusters on support surfaces have brought new insights to catalysis and highlight ways to systematic catalysts design. This review aims to provide a comprehensive bibliographic examination over the last 10 years on the development of heterogeneous catalysts, i.e., organometallic complexes or metal clusters immobilized in distinct inorganic supports such as zeolites, hierarchical zeolites, silicas, and clays. The methodologies used to prepare and/or modify the supports are critically reviewed, as well as the methods used for the immobilization of the active species. The applications of the heterogenized catalysts are presented, and some case-studies are discussed in detail.
Abstract The paper presents the results of the leaching study of Portland cement-based and zeolite-based concretes regarding water soluble hexavalent chromium. Three leaching water media (distilled water, rain water, and Britton-Robinson buffer) of various pH values were under investigation. The correlation between pH and leached-out concentrations of chromium was not confirmed. The content of hexavalent water-soluble chromium in leachates of zeolite-based concretes was found to be higher than that in leachates of Portland cement-based samples.
AbstractThis study demonstrates integration of a zeolite material in a ceramic microcomponent intended for use in sampling and analysis of environmental carbon dioxide (CO2). The zeolite material was integrated in bulk form, allowing for adsorption of large quantities of CO2 compared to previous integration attempts as thin films. To obtain a porous bulk material, an injectable slurry was developed, where expandable polymeric microspheres were added as a sacrificial template. By varying water and sphere contents of the slurry, it was possible to tune the porosity of the zeolite material between 55% and 72%. This in turn affected the flow resistance of the microcomponents, where an increase in the porosity of the filling from 62% to 72% reduced the flow resistance from 84 to 28 kPa min cm−3. In addition, the spheres facilitated complete fillings free from cracks. The zeolite material was seen to retain its ability to adsorb CO2 after processing, but it was not possible to quantify the level of retention compared to unprocessed zeolite.
[EN] In the present review, we would like to cover the most fundamental advances achieved in the design of ordered titanosilicates since the earlier discovery of TS-1 reported by EniChem in the mid-eighties. The invention of the medium-pore TS-1 zeolite was a breakthrough, and this material has been applied as efficient catalyst in diverse industrial applications. However, its limited pore size (5 5.5 Å) offers diffusion limitations when working with large molecules. The design and preparation of open titanosilicates, such as large pore molecular sieves, mesoporous ordered materials, or layered-type zeolites will be described. The applicability of these titanosilicates to catalytic oxidation processes requiring bulky organic molecules will also be presented. ; This work has been supported by the Spanish GovernmentMINECO (MAT2012-37160), Consolider Ingenio 2010-Multicat, and UPV through PAID-06-11 (n.1952). Manuel Moliner also acknowledges to ''Subprograma Ramon y Cajal'' for the contract RYC-2011-08972. ITQ thanks the ''Program Severo Ochoa'' for financial support (SEV 2012 0267). ; Moliner Marin, M.; Corma Canós, A. (2014). Advances in the synthesis of titanosilicates: From the medium pore TS-1 zeolite to highly-accessible ordered materials. Microporous and Mesoporous Materials. 189:31-40. https://doi.org/10.1016/j.micromeso.2013.08.003 ; S ; 31 ; 40 ; 189
