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.

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.

Síntese de carreadores de oxigênio à base de Ni e Co para estudo do processo de Chemical Looping usando CH4 como combustível

Increasing energy demand is being met largely by fossil fuel reserves, which emit CO2, SOx gases and various other pollutants. So does the search for fuels that emit fewer pollutants and have the same energy efficiency. In this context, hydrogen (H2) has been increasingly recognized as a potential carrier of energy for the near future. This is because the H2 can be obtained by different routes and has a wide application area , in addition to having clean burning, generating only H2O as a product of combustion , and higher energy density per unit mass . The Chemical Looping Reforming process (CLR) has been extensively investigated in recent years, it is possible to regenerate the catalyst by applying cycles of reduction and oxidation. This work has as main objective to develop catalysts based on nickel and cobalt to study the reactivity of reform with chemical recycling process. The catalysts were prepared by three different methods: combustion assisted by microwave, wet impregnation and co-precipitation. All catalysts synthesized have the same amount by weight of the active phases (60% w / w). The other 40 % m/m consists in La2O3 (8% w / w), Al2O3 (30% w / w) and MgO (2%). Oxygen carriers have been named as follows: N or C, nickel or cobalt, followed by the number 3 or 6, meaning 30 to 60% of active phase in the oxide form and C, CI or CP, which means self-combustion assisted by microwave, self-combustion assisted by microwave followed by wet impregnation and co-precipitation. The oxygen carriers were then characterized by the techniques of X-ray diffraction (XRD), surface area (BET), temperature programmed reduction (TPR) and scanning electron microscopy (SEM). The characterization results showed that the different synthesis methods have led to obtaining different morphologies and structures. Redox tests using CH4 as reducing agent and sintetic air as oxidant agent was done with N6C and C6C, N6CI and C6CI and N6CP and C6CP oxygen carriers. The tests revealed different behaviors, depending on active phase and on synthesis procedure. N6C oxygen carrier produced high levels of H2. The C6CI oxygen carrier produced CO2 and H2O without carbon deposits.

Effect of the Concentration of Siliceous Materials Added to Tobacco Cigarettes on the Composition of the Smoke Generated during Smoking

Two as-synthesized meso- and macro-porous siliceous materials (MPSMs), i.e., Al-MCM-41 and SBA-15, were mixed with tobacco to study their effect on tobacco smoke chemistry. A reference cigarette, 3R4F, and a commercial cigarette, Fortuna, containing different percentages of MPSM were smoked in a smoking machine, and the mainstream smoke was analyzed. SBA-15 showed the highest reductions of nicotine; close to 90% when it was added at 8 mass %. The superb behavior of these materials may be related to their high particulate matter filtering efficiency in combination with their catalytic activity. The selectivity of these materials with respect to nicotine was also analyzed. Al-MCM-41 presents higher selectivity for condensed compounds than for gases, whereas SBA-15 presents similar ratios for both fractions. The highest selectivity was obtained for the liquid fraction when smoking 3R4F cigarettes mixed with Al-MCM-41.

Preparação, caracterização e modificação de adsorventes para remoção de pesticidas de águas

O objectivo principal deste trabalho de mestrado consistiu em avaliar a potencial utilização de materiais adsorventes, nomeadamente, de carvões activados (AC) preparados por activação química com KOH, a partir de PET reciclado, e de materiais com estrutura mesoporosa ordenada, do tipo MCM-41 e SBA-15, na remoção de ácido 4 - cloro - 2 - metilfenoxiacético (MCPA) e de azul de metileno (MB), presentes nas águas. Nesta tese apresentam-se estudos de preparação e caracterização de materiais micro e mesoporosos e também estudos de avaliação da capacidade adsortiva em fase líquida. Prepararam-se três materiais microporosos, nomeadamente, PET-2-700, PET-2-700ox (AC oxidado) e PET-2-700red (AC reduzido), dois materiais constituídos exclusivamente por mesoporos, Si-MCM-41 e Ti-MCM-41-50 e dois materiais contendo maioritariamente mesoporos, mas que também possuem alguma microporosidade, tais corno, Si-SBA-15 e Ti-SBA-15-50. A caracterização textural dos adsorventes foi inferida por adsorção de azoto a 77K e por de difracção de raios X. Recorreu-se a três métodos de análise das isotérmicas, nomeadamente, Dubinin-Radushkevich, Brunauer-Ernrnett-Teller e alfa-s (as). A caracterização química dos AC foi realizada recorrendo-se a técnicas de análise elementar (AE) e espectroscopia de infravermelho com transformadas de Fourier (FTIR) e à determinação do ponto de carga zero. Os três carvões activados possuem valores de área superficial externa idênticos, o PET-2-700 possui o maior volume microporoso e o PET-2-700ox exibe o maior diâmetro de poros. Por outro lado, o PET-2-700ox possui um carácter fortemente ácido, o PET-2-700 exibe carácter ligeiramente ácido e o PET-2-700red apresenta propriedades ligeiramente alcalinas. Com base na AE, todas as amostras possuem percentagens de carbono elevadas, sendo que o PET-2-700red apresenta o valor mais elevado. Os resultados obtidos para a caracterização estrutural dos revelaram a obtenção de materiais mesoporosos de alta qualidade, definida pela elevada regularidade e uniformidade da estrutura porosa. A análise dos parâmetros de caracterização textura! permitiu inferir que os quatro materiais mesoporosos possuem valores de área superficial elevados, e que os materiais SBA-15 apresentam valores de volume poroso total e de tamanho de poros superiores aos manifestados pelos MCM-41. A incorporação de titânio não conduziu a uma perda significativa de qualidade dos materiais substituídos em relação às correspondentes amostras de sílica. Efectuaram-se estudos de adsorção em fase líquida de forma a avaliar a possível aplicação dos vários adsorventes na remoção de MCPA e de MB de efluentes líquidos. concluiu-se que o tempo de equilíbrio de 72 horas seria adequado e que a capacidade de adsorção dos vários AC era superior em meio ácido. Com base nas isotérmicas de adsorção do MCPA e do MB e na aplicação da representação de Langmuir e de Freundlich, foi possível concluir que o PET-2-700 possui a maior capacidade de adsorção do MCPA, 1.42 mmol/g, enquanto que o PET-2-700ox revelou a maior capacidade de adsorção do MB, 1.43 mmol/g. Na realidade, os materiais microporosos estudados apresentaram percentagens de remoção elevadas, tanto do MCPA como do MB. Relativamente aos materiais mesoporosos ordenados preparados neste trabalho, a percentagem de remoção de para os poluentes em estudo foi relativamente baixa, constatando-se que nesta fase dos estudos não constituem uma alternativa viável à utilização dos AC. No entanto, uma funcionalização criteriosa dos mesmos pode eventualmente proporcionar um aumento da capacidade adsortiva. ABSTRACT: The work presented in this master thesis, consisted of evaluating the potential use of different adsorbents materials, like activated carbon (AC) prepared by chemical activation with KOH, from recycled poly (ethylene terephthalate) (PET) and materials with ordered mesoporous structure such as MCM-41 and SBA-15, for removing acid 4-chlorine-2-metilfenoxiacétic and methylene blue from aqueous phase. We had prepared three microporous materials, PET-200-700, PET-2-700ox (AC oxidized) and PET-2-700red (reduced AC), two materials consisting exclusively of mesopores, Si-MCM-41 and Ti-MCM-41-50 and two materials containing mainly mesopores, but also having some microporosity, such as Si-SBA-15 and Ti-SBA-15-50. The textural characterization of the adsorbents was inferred by nitrogen adsorption at 77K and X-ray diffraction. Three methods were used to analyse the isotherms, namely, Dubinin-Radushkevich, Brunauer-Emmett-Teller and alpha-s (as). The chemical characterization of AC was performed using the elementary analysis, Fourier transform infrared spectroscopy (FTIR) and determination of the point of zero charge. Concerning the AC, the three present almost the same externa! surface area, PET-2-700 has a high micropore volume and PET-2-700ox shows the largest pore size diameter. On the other hand, PET-2-700ox had a strong acid character, PET-2-700 exhibits just a slightly acid character and PET-2-700red presents alkaline properties. The AE analysis allows confirming the high carbon content of theses AC, with PET-2-700red exhibiting the highest carbon proportion. The results from the structural characterization of the mesoporous materials, had disclosed the attainment of materials with high quality, defined by the raised regularity and uniformity of the porous structure. The analysis of the textural parameters allowed inferring that the four studied mesoporous materials possess high superficial area. The SBA-15 type materials present higher values of total porous volume and pores size diameter as the MCM-41. Also, the titanium incorporation did not lead to a significant loss of quality of the materials substituted in relation to the corresponding silica samples. The adsorption studies in liquid phase allow evaluating the possibility of using the different adsorbents for the MCPA and the MB removal. The kinetic studies had allowed to state the equilibrium time as 72 hours and a higher adsorption capacity was achieved in an acid medium. The influence of the pH of the medium, on the MCPA adsorption was evaluated. The MCPA and MB isotherms were analysed based on the Langmuir and Freundlich equation, the representations presented an excellent linearity, indicating the applicability of these equations to these systems. Also, it allows concluded that PET-2-700 had a higher adsorption capacity for MCPA, 1.42 mmol/g, and PET-2-700ox had a higher adsorption capacity for MB, 1.43 mmol/g. The AC used presented high removal percentages for MCPA and MB. Concerning the mesoporous materials prepared in this work, the percentage removal for the pollutants in study was relatively low, and evidencing that at the moment these mesoporous materials do not constitute a viable alternative to the AC. However, an astute funcionalisation of the same ones can, eventually provide an increase of the adsorption capacity.

Iridium(III)-surfactant complex immobilized in mesoporous silica via templated synthesis: a new route to optical materials

In this work we report the preparation of a new blue-emitting material based on the templated synthesis of mesoporous silica (MCM-41) using micellar solutions of the newly synthesized monocationic metallosurfactant complex bis[1-benzyl-4-(2,4-difluorophenyl)-1H-1,2,3-triazole](4,4'-diheptadecyl-2,2'- bipyridine)-iridium(III) chloride in hexadecyl-trimethyl-ammonium bromide (CTAB). Under ambient conditions, significant increases in excited state lifetime and quantum yield values (up to 45%), were obtained for the solid materials in comparison to the corresponding micellar solutions. Solid state (1)H and (19)F NMR spectroscopies were successfully employed for quantifying the luminophore content in terms of Ir-surfactant to CTAB and Ir-surfactant to silica ratios.

DSC estimation of structural and textural parameters of SBA-15 silica using water probe

The aim of this study was to use DSC and X-ray diffraction measurements to determine the pore size and pore wall thickness of highly ordered SBA-15 materials. The DSC curves showed two endothermic events during the heating cycle. These events were due to the presence of water inside and outside of mesopores. The results of pore radius, wall thickness and pore volume measurements were in good agreement with the results obtained by nitrogen adsorption measurement, XRD and transmission electron microscopy.

Capillary coexistence and criticality in mesopores: Modification of the Kelvin theory

The classical model of capillary equilibrium in cylindrical pores is modified here by the introduction of molecular concepts and the solid fluid interaction potential. The new approach accurately predicts capillary coexistence and criticality, with results quantitatively matching those from density functional theory for nitrogen adsorption, while also predicting condensation pressures in agreement with reported experimental findings for MCM-41. The larger critical pore size for nitrogen adsorption in these materials, however, suggests a modification of the potential function parameters, evaluated here from data for hydroxylated silica.

Thickness and stability of adsorbed film in cylindrical mesopores

The adsorbed film in small cylindrical mesopores is studied by using MCM-41 samples of uniform cylindrical channels as model systems. It is found that at a given relative pressure, the smaller the pore radius, the thicker the adsorbed film is, as postulated by Broekhoff and De Beer. Thermodynamics analysis established that the stability of the adsorbed film is determined by interface curvature and the potential of interaction between adsorbate and adsorbent. A semiempirical equation is proposed to describe the state of stable adsorbed films in cylindrical mesopores. It is also shown to be useful in calculations of pore size distributions of mesoporous solids.

Observation of a cubic phase in mesoporous silicate films grown at the air/water interface

X-Ray diffraction is reported from mesoporous silicate films grown at the air/water interface. The films were studied both as powdered films, and oriented on silicon or mica sheets. At early stages of growth we observe Bragg diffraction from a highly ordered cubic phase, with both long and short d-spacing peaks. We have assigned this as a discontinuous micellar Pm3n phase in which the silica is partly ordered. Later films retain only the known hexagonal p6m peaks and have lost any order both at short d-spacings and the longer d-spacing Bragg peaks characteristic of the cubic structure. The silica framework is considerably expanded from that in bulk amorphous silica, average Si Si distances are some 30% greater. Incorporation of glycerol or polyethylene glycol preserves the earlier cubic structure. To be consistent with earlier, in situ, X-ray and neutron reflectivity data we infer that both structures are produced after a phase transition from a less-ordered him structure late in the induction phase. The structural relations between the film Pm3n and p6m phase(s) and the known bulk SBA-1 and MCM-41 phases are briefly discussed.

A pore-size-dependent equation of state for multilayer adsorption in cylindrical mesopores

The chemical potential of adsorbed film inside cylindrical mesopores is dependent on the attractive interactions between the adsorbed molecules and adsorbent, the curvature of gas/adsorbed phase interface, and surface tension. A state equation of the adsorbed film is proposed to take into account the above factors. Nitrogen adsorption on model adsorbents, MCM-41, which exhibit uniform cylindrical channels, are used to verify the theoretical analysis. The proposed theory is capable of describing the important features of adsorption processes in cylindrical mesopores. According to this theory, at a given relative pressure, the smaller the pore radius is, the thicker the adsorbed film will be. The thickening of adsorbed films in the pores as the vapor pressure increases inevitably causes an increase in the interface curvature, which consequently leads to capillary condensation. Besides, this study confirmed that the interface tension depends substantially on the interface curvature in small mesopores. A quantitative relationship between the condensation pressure and the pore radius can be derived from the state equation and used to predict the pore radius from a condensation pressure, or vice versa.

A model for adsorption of condensable vapors on nonporous materials

A new isotherm is proposed here for adsorption of condensable vapors and gases on nonporous materials having type II isotherms according to the Brunauer-Deming-Deming-Teller (BDDH) classification. The isotherm combines the recent molecular-continuum model in the multilayer region, with other widely used models for sub-monolayer coverage, some of which satisfy the requirement of a Henry's law asymptote. The model is successfully tested using isotherm data for nitrogen adsorption on nonporous silica, carbon and alumina, as well as benzene and hexane adsorption on nonporous carbon. Based on the data fits, out of several different alternative choices of model for the monolayer region, the Freundlich and the Unilan models are found to be the most successful when combined with the multilayer model to predict the whole isotherm. The hybrid model is consequently applicable over a wide pressure range. (C) 2000 Elsevier Science B.V. All rights reserved.

Characterization of pore size distributions of mesoporous materials from adsorption isotherms

In this article, a new hybrid model for estimating the pore size distribution of micro- and mesoporous materials is developed, and tested with the adsorption data of nitrogen, oxygen, and argon on ordered mesoporous materials reported in the literature. For the micropore region, the model uses the Dubinin-Rudushkevich (DR) isotherm with the Chen-Yang modification. A recent isotherm model of the authors for nonporous materials, which uses a continuum-mechanical model for the multilayer region and the Unilan model for the submonolayer region, has been extended for adsorption in mesopores. The experimental data is inverted using regularization to obtain the pore size distribution. The present model was found to be successful in predicting the pore size distribution of pure as well as binary physical mixtures of MCM-41 synthesized with different templates, with results in agreement with those from the XRD method and nonlocal density functional theory. It was found that various other recent methods, as well as the classical Broekhoff and de Beer method, underpredict the pore diameter of MCM-41. The present model has been successfully applied to MCM-48, SBA's, CMK, KIT, HMS, FSM, MTS, mesoporous fly ash, and a large number of other regular mesoporous materials.

Adsorption hysteresis and criticality in regular mesoporous materials

In the present work, various theories predicting the critical diameter for the absence of capillary condensation and hysteresis are applied to experimental adsorption isotherms of vapors on regular mesoporous materials. Among the various theories studied, the tensile strength approximation proposed by the authors was found to be the most successful. Reversibility of nitrogen adsorption at 77.4 K was studied on pure MCM-41 of various pore sizes, as well as mixtures of pure MCM-41 samples in a 1:1 ratio. The results of PSD and hysteresis on MCM-41 mixtures are close to that expected from studies of the pure materials. The estimates of hysteresis critical temperature and diameter of MCM-41, HMS, FSM and KIT materials are also provided.

Aluminophosphate-based mesoporous molecular sieves: synthesis and characterization of TAPOs

Mesoporous Ti-substituted aluminophosphates (AlPOs) with a hexagonal, cubic and lamellar pore structure, characteristic of MCM-41, MCM-48. and MCM-50, respectively, were synthesized. The stability of these mesophases upon template removal was studied. The pore structures, surface properties, and local atom environments of Al, P, and Ti of the hexagonal and cubic Ti-containing mesoporous products were extensively characterized using X-ray diffraction, magic angle spinning nuclear magnetic resonance, AAS, XPS, ultraviolet-visible, and adsorption of nitrogen and water vapor techniques while the lamellar mesophase was not further characterized due to its very poor thermal stability. Ti-containing mesoporous AlPO materials show a reasonable thermal stability upon template removal, a hydrophilic surface property, and high porosity showing application potentials in catalytic oxidation of hydrocarbons. (C) 2001 Elsevier Science B,V. All rights reserved.