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

From Microporous to Mesoporous Molecular-Sieve Materials and Their Use in Catalysis

The chemical and catalytic activity of nanoparticles has strongly contributed to the current tremendous interest in engineered nanomaterials and often serves as a guiding principle for the design of functional materials. Since it has most recently become evident that such active materials can enter into cells or organisms, the present study investigates the level of intracellular oxidations after exposure to iron-, cobalt-, manganese-, and titania-containing silica nanoparticles and the corresponding pure oxides in vitro. The resulting oxidative stress was quantitatively measured as the release of reactive oxygen species (ROS). The use of thoroughly characterized nanoparticles of the same morphology, comparable size, shape, and degree of agglomeration allowed separation of physical (rate of particle uptake, agglomeration, sedimentation) and chemical effects (oxidations). Three sets of control experiments elucidated the role of nanoparticles as carriers for heavy metal uptake and excluded a potential interference of the biological assay with the nanomaterial. The present results indicate that the particles could efficiently enter the cells by a Trojan-horse type mechanism which provoked an up to eight times higher oxidative stress in the case of cobalt or manganese if compared to reference cultures exposed to aqueous solutions of the same metals. A systematic investigation on iron-containing nanoparticles as used in industrial fine chemical synthesis demonstrated that the presence of catalytic activity could strongly alter the damaging action of a nanomaterial. This indicates that a proactive development of nanomaterials and their risk assessment should consider chemical and catalytic properties of nanomaterials beyond a mere focus on physical properties such as size, shape, and degree of agglomeration.

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Exposure of Engineered Nanoparticles to Human Lung Epithelial Cells: Influence of Chemical Composition and Catalytic Activity on Oxidative Stress

https://www.lehigh.edu/operando/Publications/1999%20Titania-silica%20molec%20struc%20physico-chemical.pdf

Titania-silica as catalysts : molecular structural characteristics and physico-chemical properties

Publisher Summary This chapter focuses on the microporous crystalline titanium silicates. Titanium containing materials have been investigated for various reactions, but selective oxidations with H2O2 as the oxidant have attracted the most interest. For these reactions, the formation of surface titanium peroxo compounds with H2O2 and the subsequent transfer of the peroxidic oxygen to the organic reactants have been proposed to explain the mechanism by which titanium participates in the catalytic cycle. H2O2 has the advantage of giving environmentally benign water as its by-product. Furthermore, H2O2 ranks first in terms of available oxygen in the list of oxygen donors.The unusual properties of titanium silicalites have been attributed to the presence of TiIV in framework positions of the SiO2 lattice. It is important to realize that there is a limit to the extent of substitution; the exact value is still under discussion, but is certainly not more than a few percent. Very likely, the structure of crystalline silica is not stable at higher degrees of substitution. The discovery of the new titanium silicates and of their catalytic properties in H2O2 oxidation reactions has had a major impact in catalytic science and its industrial applications.

Microporous Crystalline Titanium Silicates

Degradation of Acid Orange 7 using magnetic AgBr under visible light: the roles of oxidizing species.

Titania-Silica Mixed Oxides: I. Influence of Sol-Gel and Drying Conditions on Structural Properties

Titania–Silica Mixed Oxides: IV. Influence of Ti Content and Aging on Structural and Catalytic Properties of Aerogels

Vanadia−silica mixed oxides were prepared via the sol−gel method involving acid catalysis together with prehydrolysis in order to achieve matching of the reactivities of vanadium(V) oxide triisopropoxide and tetraethoxysilicon(IV) precursors. Gelation was forced by the addition of basic solution. The as-received gels were supercritically dried by semicontinuous extraction with supercritical CO2 at 313 K (low-temperature aerogels). The effects of composition, aging, and calcination temperature on the chemical, structural, and textural properties of the solids were investigated. The oxides were characterized by N2 physisorption, XRD, vibrational spectroscopy, thermal analysis, UV−vis, and 51V NMR. The low-temperature vanadia−silica aerogels were mesoporous and highly disperse. The increasing V content from 5 to 20 wt % nominal V2O5 caused a gradual decline in V dispersion. For 30 wt % “V2O5” the continuous formation of V−O−V connectivity resulted in crystallization of V2O5. The effect of aging in basic medi...

Vanadia-silica low-temperature aerogels: Influence of aging and vanadia loading on structural and chemical properties

Titania–Silica Mixed Oxides: V. Effect of Sol-Gel and Drying Conditions on Surface Properties

The paper provides a short overview on the various Ti- and Si-containing epoxidation catalysts, with a focus on the development and characterisation of titania-silica mixed oxides prepared by the sol-gel-aerogel method. Titania-silica aerogels, dried by semicontinuous extraction of the solvent with supercritical CO2 at low temperature, possess high surface area, an amorphous mesoporous structure, and a rather even distribution of Ti in the silica matrix. The catalytic activities of mixed oxides, silica-supported titania and Ti-substituted molecular sieves (TS-1, Ti-Β and Ti-MCM-41) are compared in the epoxidation of 1-hexene, 1-octene, cyclohexene, cyclododecene and norbornene, based on literature data. The activities (i.e. the amount of converted olefin per unit time and catalyst weight) vary in a broad range of several orders of magnitude. It is shown that the low temperature aerogel containing 20 wt% TiO2 is superior to any other Ti- and Si-containing catalyst for the epoxidation of cyclic olefins. In the epoxidation of linear alkenes TS-1 has outstanding activity. Ti-substituted large and ultra-large pore molecular sieves require further development concerning their catalytic performance.

D.C.M. Dutoit

Papers

Titania-Silica Mixed Oxides: I. Influence of Sol-Gel and Drying Conditions on Structural Properties

Titania–Silica Mixed Oxides: IV. Influence of Ti Content and Aging on Structural and Catalytic Properties of Aerogels

Vanadia-silica low-temperature aerogels: Influence of aging and vanadia loading on structural and chemical properties

Titania–Silica Mixed Oxides: V. Effect of Sol-Gel and Drying Conditions on Surface Properties

Titania-silica aerogels with superior catalytic performance in olefin epoxidation compared to large pore Ti-molecular sieves