Spectroscopic Characterization of Silicalite and Titanium-Silicalite
TL;DR: In this article, the surface characterization of silicalite and titanium-silicalite is made by combined use of IR and UV-Vis reflectance spectroscopy, and the nature of the IR modes and of the electronic transitions associated with framework titanium is discussed in detail.
Abstract: Surface characterization of silicalite and titanium-silicalite is made by combined use of IR and UV-Vis reflectance spectroscopy. The nature of the IR modes and of the electronic transitions associated with framework titanium is discussed in detail. The perturbation caused by the adsorption of small polar molecules (H 2 O, NH 3 , CH 3 OH) on both the IR and UV-Vis spectra is discussed in terms of the formation of six-coordinated complexes by ligand insertion in the Ti(IV) coordination sphere. All the Ti(IV) is accessible to the interaction with the molecules.
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TL;DR: Corma et al. as mentioned in this paper used the Dupont Award on new materials (1995), and the Spanish National Award “Leonardo Torres Quevedo” on Technology Research (1996) on technology research (1996), to recognize the performance of zeolites as catalysts for oil refining and petrochemistry.
Abstract: It is possible to say that zeolites are the most widely used catalysts in industry They are crystalline microporous materials which have become extremely successful as catalysts for oil refining, petrochemistry, and organic synthesis in the production of fine and speciality chemicals, particularly when dealing with molecules having kinetic diameters below 10 A The reason for their success in catalysis is related to the following specific features of these materials:1 (1) They have very high surface area and adsorption capacity (2) The adsorption properties of the zeolites can be controlled, and they can be varied from hydrophobic to hydrophilic type materials (3) Active sites, such as acid sites for instance, can be generated in the framework and their strength and concentration can be tailored for a particular application (4) The sizes of their channels and cavities are in the range typical for many molecules of interest (5-12 A), and the strong electric fields2 existing in those micropores together with an electronic confinement of the guest molecules3 are responsible for a preactivation of the reactants (5) Their intricate channel structure allows the zeolites to present different types of shape selectivity, ie, product, reactant, and transition state, which can be used to direct a given catalytic reaction toward the desired product avoiding undesired side reactions (6) All of these properties of zeolites, which are of paramount importance in catalysis and make them attractive choices for the types of processes listed above, are ultimately dependent on the thermal and hydrothermal stability of these materials In the case of zeolites, they can be activated to produce very stable materials not just resistant to heat and steam but also to chemical attacks Avelino Corma Canos was born in Moncofar, Spain, in 1951 He studied chemistry at the Universidad de Valencia (1967−1973) and received his PhD at the Universidad Complutense de Madrid in 1976 He became director of the Instituto de Tecnologia Quimica (UPV-CSIC) at the Universidad Politecnica de Valencia in 1990 His current research field is zeolites as catalysts, covering aspects of synthesis, characterization and reactivity in acid−base and redox catalysis A Corma has written about 250 articles on these subjects in international journals, three books, and a number of reviews and book chapters He is a member of the Editorial Board of Zeolites, Catalysis Review Science and Engineering, Catalysis Letters, Applied Catalysis, Journal of Molecular Catalysis, Research Trends, CaTTech, and Journal of the Chemical Society, Chemical Communications A Corma is coauthor of 20 patents, five of them being for commercial applications He has been awarded with the Dupont Award on new materials (1995), and the Spanish National Award “Leonardo Torres Quevedo” on Technology Research (1996) 2373 Chem Rev 1997, 97, 2373−2419
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TL;DR: The available technologies for the abatement of phenol from water and gaseous streams are briefly reviewed, and the recent advancements summarized.
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TL;DR: In this paper, the similarities and differences in structural characteristics and physico-chemical properties between titania-silica mixed and supported oxides are emphasized, and the generation of new catalytic active sites either on the silica surface or in the matrix is discussed with respect to the formation of Ti-O-Si bonds and the local structure.
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TL;DR: This review is focused on the use of solid Lewis acids to promote catalytic oxidations, and the core of the review is organized to show the evolution from the simplest strategy for heterogeneizing homogeneous catalysts, to the more elaborate ones in which the active sites are part of the solid structure.
Abstract: This review is focused on the use of solid Lewis acids to promote catalytic oxidations. While the concept of using Lewis acids to promote the reaction of organic substrates with oxidizing reagents is widely accepted in homogeneous catalysis, this concept has not become evident and generally used in heterogeneous catalysis until recent days. Certainly the development of new Lewis acid solids active and selective for catalytic oxidations is an urgent need and a challenging scientific target for some substrates especially using environmentally friendly oxidants. Since the replacement of current stoichiometric oxidations for the production of fine chemicals by environmentally benign catalytic oxidations is one of the major tasks in green chemistry, solid Lewis acids are called to play a crucial role to accomplish this goal. In the review, we will see the still important role that stoichiometric oxidations play in our daily life, and how they are being substituted by catalytic oxidations. At this point, three general mechanisms in which Lewis acids are involved will be described, and the material has been organized starting from homogeneous and ending with solid catalysts for heterogeneous oxidations. A bridge between the two will be established by presenting catalytic systems that can fill the gap between the two systems helping to rationalize the nature of the catalytic active sites in solid systems. This review is obviously focused on solid oxidation catalysts, and the core of the review is organized to show the evolution from the simplest strategy for heterogeneizing homogeneous catalysts, i.e., supporting the active species on large surface area solids, to the more elaborate ones in which the active sites are part of the solid structure. Given the importance of metallosilicates, and more specifically titanosilicates, as catalysts in commercial processes, special attention has been paid to these types of materials. Although sufficient references are provided to early seminal work, special emphasis has been given to most recent contributions to this area, particularly of the last 10 years. Patent literature has also been extensively covered in this review. Examples to illustrate the concepts have been selected among recent publications, and an effort has been made to present a series of commercial and near commercial processes based on catalytic oxidations. Finally, two * E-mail: acorma@itq.upv.es. 3837 Chem. Rev. 2002, 102, 3837−3892
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Abstract: (Article begins on next page) Anyone can freely access the full text of works made available as \"Open Access\". Works made available under a Creative Commons license can be used according to the terms and conditions of said license. Use of all other works requires consent of the right holder (author or publisher) if not exempted from copyright protection by the applicable law. Availability: This is the author's manuscript
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1,293 citations
TL;DR: In this article, a new polymorph of SiO2 (silicalite, refractive index 1.39, density 1.76 g cm−3) has been proposed, which encloses a three-dimensional system of intersecting channels defined by 10-rings wide enough to adsorb molecules up to 0.6 nm diameter.
Abstract: A new polymorph of SiO2 (silicalite, refractive index 1.39, density 1.76 g cm−3) has a novel topologic type of tetrahedral framework. This encloses a three-dimensional system of intersecting channels defined by 10-rings wide enough to adsorb molecules up to 0.6 nm diameter. Silicalite is hydrophobic and organophilic, and selectively adsorbs organic molecules over water.
1,208 citations
TL;DR: The characteristic properties of zeolites, such as acidity, shape-selectivity and thermal stability, also enable them to be used for highly selective synthesis in the fields of chemical intermediates and fine chemicals as mentioned in this paper.
Abstract: Zeolites have proved to be valuable technical catalysts in petrochemistry and in oil processing. The characteristic properties of zeolites, such as acidity, shape-selectivity and thermal stability also enable them to be used for highly selective synthesis in the fields of chemical intermediates and fine chemicals. This interesting area of application has grown continuously in recent years. The present article summarizes the various standard types of reaction involved in organic syntheses which can be catalyzed by zeolites; these include, inter alia, electrophilic and nucleophilic substitution reactions, isomerization of double bonds and carbon skeletons, as well as addition, elimination and hydrogenation reactions.
454 citations
TL;DR: The mid i.r. spectra have been recorded of the pentasil family, of the mordenite group, of ZSM-39 and Melanophlogite as mentioned in this paper.
300 citations
09 Mar 2007
TL;DR: In this paper, it was shown that the Laporte-forbidden bands of transition group complexes can be adapted to the strong Laportes-allowed bands, at least in the octahedral complexes of a central ion with six halide ligands.
Abstract: W H I L E the weak, Laporte-forbidden bands of transition group complexes have been successfully described by the ligand field theory, with the interest concentrated on the partly filled shell, it has only recently been demonstrated that M.O. theory is equally well adapted to the strong, Laporte-allowed bands, at least in the octahedral complexes of a central ion with six halide ligands. Qualitatively, a satisfactory description of these strong bands may be given by saying that their wave number decreases, the more oxidizing the central ion and the more reducing the ligands. This is exactly as expected for electron transfer from the ligand to the central ion during optical excitation. It is a redox process, decreasing the oxidation number of the central ion by one, while the ligand field bands correspond to the same oxidation number in the excited and the ground state. Consequently, the d n -systems with η < 10, i.e. a partly filled shell which can take up an electron, have the much lower wave numbers of these bands than the corresponding d 1 0 -systems. Two review papers have been written by Rabinowitch (1942) and Orgel (1954). However, these papers were not very much concerned with complexes of metals, but rather with the absorption spectra of crystalline, dissolved and gaseous alkali halides, and with some molecular addition compounds occurring in organic chemistry, etc. There has always been a close connexion between the study of electron transfer spectra and photochemical reactions: the change of oxidation number in the excited state may make it chemically a very reactive entity; other reactions may be started, or ligands dissociated off, often with changed oxidation number. Fajans, Fromherz, and their assistants made a thorough study of the halide complexes of d 1 0 -systems such as Cu(I), Ag(I), Hg(II), and d 1 0 s 2 -systems such as Sn(II), T1(I), Pb(II). In this way, some confusion arose between the genuine electron transfer bands of the former systems and the particular s 2 -> sp transitions to be discussed in the next chapter, in the latter case. However, it was realized that the bands of CI", Br" and I" (as known in aqueous solution or in
248 citations