Estudo de materiais mesoporosos funcionalizados com diferentes aminas para captura do dióxido de carbono através do processo de adsorção

Intensive use of machinery and engines burning fuel dumps into the atmosphere huge amounts of carbon dioxide (CO2), causing the intensification of the greenhouse effect. Climate changes that are occurring in the world are directly related to emissions of greenhouse gases, mainly CO2, gases, mainly due to the excessive use of fossil fuels. The search for new technologies to minimize the environmental impacts of this phenomenon has been investigated. Sequestration of CO2 is one of the alternatives that can help minimize greenhouse gas emissions. The CO2 can be captured by the post-combustion technology, by adsorption using adsorbents selective for this purpose. With this objective, were synthesized by hydrothermal method at 100 °C, the type mesoporous materials MCM - 41 and SBA-15. After the synthesis, the materials were submitted to a calcination step and subsequently functionalized with different amines (APTES, MEA, DEA and PEI) through reflux method. The samples functionalized with amines were tested for adsorption of CO2 in order to evaluate their adsorption capacities as well, were subjected to various analyzes of characterization in order to assess the efficiency of the method used for functionalization with amines. The physic-chemical techniques were used: X- ray diffraction (XRD), nitrogen adsorption and desorption (BET/BJH), scanning electron microscopy (SEM), transmission electron microscopy (TEM), CNH Analysis, Thermogravimetry (TG/DTG) and photoelectron spectroscopy X-ray (XPS). The CO2 adsorption experiments were carried out under the following conditions: 100 mg of adsorbent, at 25 °C under a flow of 100 ml/min of CO2, atmospheric pressure and the adsorption variation in time 10-210 min. The X-ray diffraction with the transmission electron micrographs for the samples synthesized and functionalized, MCM-41 and SBA-15 showed characteristic peaks of hexagonal mesoporous structure formation, showing the structure thereof was obtained. The method used was efficient reflux according to XPS and elemental analysis, which showed the presence of amines in the starting materials. The functionalized SBA -15 samples were those that had potential as best adsorbent for CO2 capture when compared with samples of MCM-41, obtaining the maximum adsorption capacity for SBA-15-P sample

Derivati polimerici organometallici ancorati su matrice inorganica per applicazioni in chimica fine

Organotin compounds have found in the last few decades a wide variety of applications. Indeed, they are used successfully as antifouling paints, PVC stabilizers and ion carriers, as well as homogeneous catalysts. In this context, it has been proved that the Lewis acidity of the metal centre allows these compounds to promote the reaction between alcohol and ester. However their use is now limited by their well-known toxicity, moreover they are hardly removable from the reaction mixture. This problem can be overcome by grafting the organotin derivative onto a polymeric cross-linked support. In this way the obtained heterogeneous catalyst can be easily filtered off from the reaction mixture, thus creating the so-called "clean organotin reagents", avoiding the presence of toxic organotin residues in solution and the tin release in the environment. In the last few years several insoluble polystyrene resins containing triorganotin carboxylate moieties have been synthesized with the aim of improving their catalytic activity: in particular we have investigated and opportunely modified their chemical structure in order to optimize the accessibility to the metal centre and its Lewis acidity. Recently, we replaced the polymeric matrix with an inorganic one, in order to dispose of a relatively cheaper and easily available support. For this purpose an ordered mesoporous silica, characterized by 2D-hexagonal pores, named MCM-41, and an amorphous silica have been selected. In the present work two kinds of MCM-41 silica containing the triorganotin carboxylate moiety have been synthesized starting from a commercial Cab-O-Sil M5 silica. These catalysts have two different spacers between the core and the tin-carboxylate moiety, namely a polyaliphatic chain (compound FT29) or a poliethereal one (compound FT6), with the aim to improve the interaction between catalyst and reacting ester. Three catalysts supported onto an amorphous silica have been also synthesized: the structure is the same as silica FT29, i.e. a compound having a polialiphatic chain, and they have different percentage of organotin derivative grafted on the silica surface (10, 30, 50% respectively for silica MB9, SU27 and SU28). The performances of the above silica as heterogeneous catalysts in transesterification reactions have been tested in a model reaction between ethyl acetate and 1-octanol, a primary alcohol sensitive to the reaction conditions. The alcohol conversion was assessed by gas-chromatography, determining the relative amount of transesterified product and starting alcohol after established time intervals.

Inverse size exclusion chromatography (ISEC)

In this work, an improved protocol for inverse size-exclusion chromatography (ISEC) was established to assess important pore structural data of porous silicas as stationary phases in packed chromatographic columns. After the validity of the values generated by ISEC was checked by comparison with data obtained from traditional methods like nitrogen sorption at 77 K (Study A), the method could be successfully employed as valuable tool at the development of bonded poly(methacrylate)-coated silicas, while traditional methods generate partially incorrect pore structural information (Study B). Study A: Different mesoporous silicas were converted by a pseudomorphical transition into ordered MCM-41-type silica while maintaining the particle-size and -shape. The essential parameters like specific surface area, average pore diameter and specific pore volume, the pore connectivity from ISEC remained nearly the same which was reflected by the same course of the theoretical plate height vs. linear velocity curves. Study B: In the development of bonded poly(methacrylate)-coated silicas for the reversed phase separation of biopolymers, ISEC was the only method to generate valid pore structural information of the polymer-coated materials. Synthesis procedures were developed to obtain reproducibly covalently bonded poly(methacrylate) coatings with good thermal stability on different base materials, employing as well particulate and monolithic materials.

Development of innovative catalysts for the hydrodechlorination to fluoroethers

In this work the hydrodechlorination of CF3OCFClCF2Cl to produce unsaturated CF3OCF=CF2 was studied over a series of supported metal catalysts. Currently this molecule is produced from the precursor CF3OCFClCF2Cl by dechlorination with zinc powder. An important cost on the economic and environmental balance is represents by the large amount of ZnCl2 produced and to be disposed of. A new approach, based on gas-phase hydrodechlorination over supported catalysts can lead to a new sustainable process. During the feasibility step of this project, substantially two kind of materials were studied: metals supported over activated carbon and Pd/Cu species supported over MCM-41 mesoporous silica. Observed catalytic performances were strongly dependent on the metal and support used. All carbon-supported Ru, Pd, and bimetallic catalysts are fairly active and yielded the target product CF3OCF=CF2, the higher selectivity being obtained with ruthenium- and palladium-based materials. Nevertheless, Ru-based catalysts showed poor stability and this deactivation may be attributed to the deposition of chlorinated organic species blocking the active sites. On the other hand, palladium-containing catalysts showed high stability. Ru/Pd and Pd/Cu bimetallic catalysts exhibited long-term selectivity and stability, highlighting the possibility for these materials to be employed in the CF3OCF=CF2 production process. During the second part of this thesis, a series of bimetallic meso-structured Pd/Cu MCM-41 catalysts were studies to overcome possible mass transfer limitations. The materials were obtained by different synthesis methods. The incorporation of Pd and Cu during MCM-41 synthesis, did not destroy the typical hexagonal array and ordered pore system of MCM-41. However, the calcination for the removal of the template provoked significant segregation of oxides. The impregnation leads to pore-occlusion and formation of Cu particles and large bimetallic PdCu species. Larger metal particles leads to lower CF3OCFClCF2Cl conversion, while the monometallic particles can decrease the selectivity to CF3OCF=CF2, fostering the dehalogenation to CF3OCH=CF2.

Sintesi e caratterizzazione di sistemi catalitici a base di pd-cu e loro utilizzo nella reazione di idrodeclorurazione di molecole clorofluorurate

Questo lavoro di tesi ha avuto come obiettivo quello di individuare e studiare diverse strategie di sintesi per la preparazione di catalizzatori a base di Pd-Cu supportati su materiali mesoporosi a basi di SiO2. Queste strategie sono state mirate a migliorare: -Distribuzione della fase metallica attiva e la sua accessibilità; -Formazione della fase mista Pd-Cu; -Dimensione delle specie metalliche sulla superficie; -Differenti caratteristiche morfologiche del supporto. I diversi catalizzatori preparati sono stati poi testati sulla reazione di idrodeclorurazione del 1,2-dicloro-1,1,2-trifluoro-2-(triflurometossi)etano (AM), svolta in fase gas con idrogeno a pressione atmosferica, con lo scopo di ottenere il composto insaturo corrispondente 1,1,2-trifluoro-2-(trifluorometossi)etene (MVE). Attualmente, il processo industriale per la produzione di MVE, è condotto con l’utilizzo di quantità stechiometriche di Zn in dimetilformammide; questo processo a causa delle quantità stechiometriche di ZnCl2 prodotto e dell'elevato consumo di solvente tossico risulta assai dispendioso dal punto di vista economico ed ambientale. La tipologia di materiali microporosi, già investigata, può limitare l'efficienza verso substrati ingombranti, è quindi interessante investigare catalizzatori con dimensione dei pori mesoporosi a base di silice; in particolare sono stati analizzati MCM-41 e silice amorfa GRACE® DAVICAT - 1401. In particolare, durante il lavoro di tesi sono stati sviluppati i seguenti argomenti: 1.Studio degli effetti della metodologia di sintesi e del contenuto metallico sui parametri chimico-fisici e catalitici dei sistemi a base di Pd-Cu supportati su MCM-41 e GRACE® DAVICAT - 1401; 2.Ottimizzazione del processo di sintesi dei supporti di MCM-41, ponendo attenzione alle quantità dei reagenti utilizzati, alla metodologia di eliminazione del templante e al tempo di trattamento idrotermale; 3.Ottimizzazione del processo di sintesi dei sistemi catalitici a base di Pd-Cu, al fine di ottenere una fase attiva costituita da particelle con dimensioni ridotte composte da una fase mista Pd-Cu.

Ligand tethering by ion-exchange for the immobilization of homogeneous catalysts

A Rh phosphine complex, derived from the Wilkinson’s catalyst, has been immobilized by ion-exchange on the ammonium form of a Al-MCM-41 sample. Ammonium ions have been exchanged by cholamine ions, which act as an amine ligand, and then the Wilkinson’s catalyst has been immobilized by substitution of a phosphine ligand by the anchored amine. This is a novel immobilization procedure, as a ligand, instead of the whole complex, is tethered to the support by ion exchange. The obtained hybrid catalyst has been characterized by Elemental Analysis, DRIFTS and XPS. The quantitative exchange of ammonium by cholamine and coordination of Rh to amines has been observed. Most of the anchored Rh is considered to be coordinated to the ligand tethered to the support and a small proportion seems to be interacting with the protonated ligand or with the support surface. The catalyst has been tested in the hydrogenation of cyclohexene and in the hydroformylation of 1-octene. In the first case the catalyst is active and reusable, while a strong Rh leaching takes place in the second one.

Degradación de efluentes de las industrias del cuero y textil mediante procesos fotocatalíticos heterogéneos empleando la luz solar.

El creciente desarrollo de la industria del cuero y textil en nuestro país, y específicamente en la provincia de Córdoba, ha hecho resurgir en los ultimos años una problemática aún no resuelta que es la elevada contaminación de los recursos hídricos. En ambas industrias, la operación de teñido involucra principalmente colorantes de tipo azoico los cuales son "no biodegradables" y se fragmentan liberando aminas aromáticas cancerígenas. Para abordar esta problemática, la fotocatálisis heterogénea aparece como una nueva tecnología que permitiría la completa mineralización de estos colorantes. A través de radiación y un fotocatalizador sólido adecuado se pueden generan radicales libres eficientes para la oxidación de materia orgánica (colorantes) en medio acuoso. En este sentido, se proponen tamices moleculares mesoporosos modificados con metales de transición (MT) como fotocatalizadores potencialmente aptos para la degradación de estos contaminantes. El propósito principal de este proyecto es el diseño, síntesis, caracterización y evaluación de materiales mesoporosos que presenten actividad fotocatalítica ya sea mediante la modificación de su estructura con diversos metales fotosensibles y/o empleándolos como soporte de óxido de titanio. Se pretende evaluar estos materiales en la degradación de colorantes intentando desplazar su fotosensibilidad hacia la radiación visible para desarrollar nuevas tecnologías con menor impacto ambiental y mayor aprovechamiento de la energía solar. Para ello se sintetizarán materiales del tipo MCM-41 modificados con distintos MT tales como Fe, Cr, Co, Ni y Zn mediante incorporación directa del ión metálico o impregnación. Al mismo tiempo, tanto estos últimos materiales como el MCM-41 silíceo serán empleados como soporte de TiO2. Sus propiedades fisicoquímicas se caracterizarán mediante distintas técnicas instrumentales y su actividad fotocatalítica se evaluará en la degradación de colorantes azoicos bajo radiación visible. Se seleccionará el catalizador más eficiente y se estudiarán los diversos factores que afectan el proceso de fotodegradación. Así mismo, el análisis de la concentración del colorante y los productos presentes en el medio en función del tiempo de reacción permitirá inferir sobre la cinética de la decoloración y postular posibles mecanismos de fotodegradación. Con esta propuesta se espera contribuír al desarrollo de un sector industrial importante en nuestra provincia como es el de las industrias del cuero y textil, mediante la generación de nuevas tecnologías que empleen la energía solar para la degradación de sus efluentes (colorantes). En este sentido, se espera desarrollar nuevos materiales optimizados para lograr la mayor eficiencia fotocatalítica. Esto conduciría entonces hacia la remediación de un problema ambiental de alto impacto tanto para nuestra provincia y nuestro país como para la población mundial, como es la contaminación de los recursos hídricos. Finalmente, con este proyecto se contribuirá a la formación de dos doctorandos y un maestrando, cuyos temas de tesis están vinculados con nuestro objeto de estudio.

Síntesis y caracterización de Materiales Nanoscópicos y Nano-especies activas y sus aplicaciones en Energía y Medio Ambiente

Se estudiara la síntesis, caracterización y aplicación de Materiales Nanoscópicos (Nanoestructurados, MN y Nanocomposites, NC), con propiedades definidas en el campo de la Energía, Medio Ambiente y Bioingeniería, especialmente las MCM y SBA ( MCM-41 y MCM-48, SBA-1, SBA-3, SBA-15 y SBA-16, Silíceas o Al/Ga/Ti como Heteroátomo, y la Al-SBA-3, recientemente desarrollada por nosotros, primera publicación a nivel mundial). Se pondrá énfasis en el diseño, preparación y caracterización de sus réplicas con C (CMK-1 y CMK-3). Determinación y optimización de las estrategias de síntesis de MN y NC y Nano especies Activas en nuevos catalizadores (Ir/ TiO2, Pt/Pd etc.), cuyas propiedades fundamentales (estructurales, electrónicas, conductividad, actividad catalítica, etc.) sean aplicables en los Campos Citados. Comprensión de los parámetros que definen dichas propiedades, relación estructura/actividad, rediseño y aplicaciones de MN y NC en dos procesos específicos (de los cuales ya hemos publicado resultados): Energía y Medioambiente: 1) Almacenamiento de H2, Adsorción/Absorción de H2 en los MN Silíceos y Carbonosos y NC y Desarrollo de NC híbridos formados por reservorios en base a los MN por oclusión de nano-alambres moleculares de polímeros orgánicos, modificando las propiedades de conductividad / semiconductividad y adsorción de H2; 2) Estudio de las reacciones de hidrotratamiento catalítico (HDT), que comprende la hidrogenación, la hidrodesulfurizacion (HDS) y la hidrodenitrogenacion (HDN) de compuestos refractarios presentes en los cortes de combustibles. La determinación del mecanismo de las reacciones de HDS y HDN.

Application of density functional theory to capillary phenomena in cylindrical mesopores with radial and longitudinal density distributions

In this paper, we applied a version of the nonlocal density functional theory (NLDFT) accounting radial and longitudinal density distributions to study the adsorption and desorption of argon in finite as well as infinite cylindrical nanopores at 87.3 K. Features that have not been observed before with one-dimensional NLDFT are observed in the analysis of an inhomogeneous fluid along the axis of a finite cylindrical pore using the two-dimensional version of the NLDFT. The phase transition in pore is not strictly vapor-liquid transition as assumed and observed in the conventional version, but rather it exhibits a much elaborated feature with phase transition being complicated by the formation of solid phase. Depending on the pore size, there are more than one phase transition in the adsorption-desorption isotherm. The solid formation in finite pore has been found to be initiated by the presence of the meniscus. Details of the analysis of the extended version of NLDFT will be discussed in the paper. (C) 2004 American Institute of Physics.

Diffusion of linear paraffins in nanoporous silica

The diffusion of hexane, heptane, octane, and decane in nanoporous MCM-41 silica at various temperatures is investigated by the zero-length-column method. The diffusion coefficients are derived by a complete-time-range analysis of desorption curves at different purge flow rates and temperatures. The results show that the calculated low-coverage diffusivity values decrease monotonically, and the derived Henry's law constants increase, as the carbon number of paraffins increases. The study reveals that transport is strongly influenced by intracrystalline diffusion and dominated by the sorbate-sorbent interaction. The diffusion activation energy and adsorption isosteric heat at zero loading increase monotonically with the carbon number of linear paraffins, but their ratio is essentially constant for each adsorbate compound.

Capillary phenomena in the framework of the two-dimensional density functional theory

We present results of application of the density functional theory (DFT) to adsorption and desorption in finite and infinite cylindrical pores accounting for the density distribution in radial and axial directions. Capillary condensation via formation of bridges is considered using canonical and grand canonical versions of the 2D DFT. The potential barrier of nucleation is determined as a function of the bulk pressure and the pore diameter. In the framework of the conventional assumptions on intermolecular interactions both 1D and 2D DFT versions lead to the same results and confirm the classical scenario of condensation and evaporation: the condensation occurs at the vapor-like spinodal point, and the evaporation corresponds to the equilibrium transition pressure. The analysis of experimental data on argon and nitrogen adsorption on MCM-41 samples seems to not completely corroborate this scenario, with adsorption branch being better described by the equilibrium pressure - diameter dependence. This points to the necessity of the further development of basic representations on the hysteresis phenomena.

Modeling nitrogen adsorption in spherical pores of siliceous materials by density functional theory

Adsorption of nitrogen in spherical pores of FDU-1 silica at 77 K is considered by means of a nonlocal density functional theory (NLDFT) accounting for a disordered structure of pore walls. Pore size distribution analysis of various FDU-1 samples subject to different temperatures of calcination revealed three distinct groups of pores. The principal group of pores is identified as ordered spherical mesopores connected with each other by smaller interconnecting pores and irregular micropores present in the mesopore walls. To account for the entrances (connecting pores) into spherical mesopores, a concept of solid mass distribution with respect to the apparent density was introduced. It is shown that the introduction of the aforementioned distribution was sufficient to quantitatively describe experimental adsorption isotherms over the entire range of relative pressures spanning six decades.

Pore size characterization of mesoporous materials by a thermodynamic approach: A curvature-dependent solid-fluid potential

A thermodynamic analysis of nitrogen adsorption in cylindrical pores of MCM-41 and SBA-15 samples at 77 K is presented within the framework of the Broekhoff and de Boer (BdB) theory. We accounted for the effect of the solid surface curvature on the potential exerted by the pore walls. The developed model is in quantitative agreement with the non-local density functional theory (NLDFT) for pores larger than 2 tun. This modified BdB theory accounting for the Curvature Dependent Potential (CDP-BdB) was applied to determine the pore size distribution (PSD) of a number of MCM-41 and SBA-15 samples on the basis of matching the equilibrium theoretical isotherm against the adsorption branch of the experimental isotherm. In all cases investigated the PSDs determined with the new approach are very similar to those determined with the non-local density functional theory also using the same basis of matching of theoretical isotherm against the experimental adsorption branch. The developed continuum theory is very simple in its utilization, suggesting that CDP-BdB could be used as an alternative tool to obtain PSD for mesoporous solids from the analysis of adsorption branch of adsorption isotherms of any sub-critical fluids.

Modeling of adsorption and nucleation in infinite cylindrical pores by two-dimensional density functional theory

In this paper, we present an analysis of argon adsorption in cylindrical pores having amorphous silica structure by means of a nonlocal density functional theory (NLDFT). In the modeling, we account for the radial and longitudinal density distributions, which allow us to consider the interface between the liquidlike and vaporlike fluids separated by a hemispherical meniscus in the canonical ensemble. The Helmholtz free energy of the meniscus was determined as a function of pore diameter. The canonical NLDFT simulations show the details of density rearrangement at the vaporlike and liquidlike spinodal points. The limits of stability of the smallest bridge and the smallest bubble were also determined with the canonical NLDFT. The energy of nucleation as a function of the bulk pressure and the pore diameter was determined with the grand canonical NLDFT using an additional external potential field. It was shown that the experimentally observed reversibility of argon adsorption isotherms at its boiling point up to the pore diameter of 4 nm is possible if the potential barrier of 22kT is overcome due to density fluctuations.

Modeling of adsorption in finite cylindrical pores by means of density functional theory

Adsorption of argon at its boiling point infinite cylindrical pores is considered by means of the non-local density functional theory (NLDFT) with a reference to MCM-41 silica. The NLDFT was adjusted to amorphous solids, which allowed us to quantitatively describe argon adsorption isotherm on nonporous reference silica in the entire bulk pressure range. In contrast to the conventional NLDFT technique, application of the model to cylindrical pores does not show any layering before the phase transition in conformity with experimental data. The finite pore is modeled as a cylindrical cavity bounded from its mouth by an infinite flat surface perpendicular to the pore axis. The adsorption of argon in pores of 4 and 5 nm diameters is analyzed in canonical and grand canonical ensembles using a two-dimensional version of NLDFT, which accounts for the radial and longitudinal fluid density distributions. The simulation results did not show any unusual features associated with accounting for the outer surface and support the conclusions obtained from the classical analysis of capillary condensation and evaporation. That is, the spontaneous condensation occurs at the vapor-like spinodal point, which is the upper limit of mechanical stability of the liquid-like film wetting the pore wall, while the evaporation occurs via a mechanism of receding of the semispherical meniscus from the pore mouth and the complete evaporation of the core occurs at the equilibrium transition pressure. Visualization of the pore filling and empting in the form of contour lines is presented.