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

Liquid hydrocarbon fuels play an essential part in the global energy chain, owing to their high energy density and easy transportability. Olefins play a similar role in the production of consumer goods. In a post-oil society, fuel and olefin production will rely on alternative carbon sources, such as biomass, coal, natural gas, and CO(2). The methanol-to-hydrocarbons (MTH) process is a key step in such routes, and can be tuned into production of gasoline-rich (methanol to gasoline; MTG) or olefin-rich (methanol to olefins; MTO) product mixtures by proper choice of catalyst and reaction conditions. This Review presents several commercial MTH projects that have recently been realized, and also fundamental research into the synthesis of microporous materials for the targeted variation of selectivity and lifetime of the catalysts.

Conversion of Methanol to Hydrocarbons: How Zeolite Cavity and Pore Size Controls Product Selectivity

Organic Carbonates as Solvents in Synthesis and Catalysis

Ocean acidification and climate change are expected to be two of the most difficult scientific challenges of the 21st century. Converting CO2 into valuable chemicals and fuels is one of the most practical routes for reducing CO2 emissions while fossil fuels continue to dominate the energy sector. Reducing CO2 by H2 using heterogeneous catalysis has been studied extensively, but there are still significant challenges in developing active, selective and stable catalysts suitable for large-scale commercialization. The catalytic reduction of CO2 by H2 can lead to the formation of three types of products: CO through the reverse water–gas shift (RWGS) reaction, methanol via selective hydrogenation, and hydrocarbons through combination of CO2 reduction with Fischer–Tropsch (FT) reactions. Investigations into these routes reveal that the stabilization of key reaction intermediates is critically important for controlling catalytic selectivity. Furthermore, viability of these processes is contingent on the development of a CO2-free H2 source on a large enough scale to significantly reduce CO2 emissions.

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Catalytic reduction of CO2 by H2 for synthesis of CO, methanol and hydrocarbons: challenges and opportunities

This paper reviews recent studies on the semiconductor photocatalysis based on surface-modified TiO2 of which application is mainly focused on environmental remediation. TiO2 photocatalysis that is based on the photoinduced interfacial charge transfer has been extensively studied over the past four decades. A great number of modification methods of semiconductor photocatalysts have been developed and investigated to accelerate the photoconversion, to enable the absorption of visible light, or to alter the reaction mechanism to control the products and intermediates. In this regard, various modification methods of TiO2 are classified according to the kind of surface modifiers (metal-loading, impurity doping, inorganic adsorbates, polymer coating, dye-sensitization, charge transfer complexation) and their effects on photocatalytic reaction mechanism and kinetics are discussed in detail. Modifying TiO2 in various ways not only changes the mechanism and kinetics under UV irradiation but also introduces visible light activity that is absent with pure TiO2. Each modification method influences the photocatalytic activity and mechanism in a way different from others and the observed modification effects are often different depending on the test substrates and conditions even for the same modification method. Better understanding of the modification effects on TiO2 photocatalysis is necessary to obtain reliable results, to assess the photoconversion efficiency more quantitatively, and to further improve the modification methods.

Surface modification of TiO2 photocatalyst for environmental applications

Methane dehydro-aromatization over Mo/HZSM-5 in the absence of oxygen : A multinuclear solid-state NMR study of the interaction between supported Mo species and HZSM-5 zeolite with different crystal sizes

Variations in the structure and acidity properties of HZSM‐5 zeolites with reduction in crystal sizes down to nanoscale (less than 100 nm) have been investigated by XRD, TEM and solid‐state NMR with a system capable of in situ sample pretreatment. As evidenced by a combination of 27Al MAS NMR, 29Si MAS, CP/MAS NMR and 1H MAS NMR techniques, the downsize of the zeolite crystal leads to an obvious line broadening of the 27Al, 29Si MAS NMR spectrum, an increasing of the silanol concentration on the external surface, and a pronounced alteration of the acidity distribution between the external and internal surfaces of the zeolite. In a HZSM‐5 zeolite with an average size at about 70 nm, the nonacidic hydroxyl groups (silanols) are about 14% with respect to the total amount of Si, while only 4% of such hydroxyl groups exist in the same kind of zeolite at 1000 nm crystal size. The result of 1H MAS NMR obtained using Fluorinert® FC‐43 (perfluorotributyl amine) as a probe molecule demonstrates that most of the silanols are located on the external surface of the zeolite. Moreover, the concentration of Bronsted acid sites on the external surface of the nano‐structured zeolite appears to be distinctly higher than that of the microsized zeolite.

A high-resolution solid-state NMR study on nano-structured HZSM-5 zeolite

Mild oxidation of thiophene over TS-1/H2O2

High effective dehydration of bio-ethanol into ethylene over nanoscale HZSM-5 zeolite catalysts

Small-crystal titanium silicalite-1 (TS-1) with a crystal size of about 600 nm × 400 nm × 250 nm, was treated with different organic bases, including ethylamine, diethylamine, tetramethyl ammonium hydroxide, tetrapropyl ammonium hydroxide and tetrabutyl ammonium hydroxide. The treated TS-1 was characterized by X-ray powder diffraction (XRD), Fourier-transform infrared spectrum (FTIR), ultraviolet–visible diffuse reflectance spectrum (UV–vis), X-ray photoelectron spectrum (XPS), n -hexane and cyclohexane physical adsorption, nitrogen physisorption, inductive coupled plasma emission (ICP), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Modification with different bases led to different molar ratios of Si/Ti on the external surface, according to the XPS data. The TEM images showed that many irregular hollows were generated during modification, due to the random dissolution of framework silicon and titanium. The dissolved amorphous silica and titania recrystallize on the external surface of the TS-1 crystals in the presence of template, and different axis-oriented recrystallization occurred for different templates. Tetrapropyl ammonium favored a -orientation and tetrabutyl ammonium favored b -orientation. Especially the modification with tetrapropyl ammonium hydroxide improved the catalytic properties of small-crystal TS-1 for the hydroxylation of phenol. The conversion of phenol reached 32.6% over small-crystal TS-1 modified with 0.06 mol/L tetrapropyl ammonium hydroxide for 72 h.

Xiangsheng Wang

Papers

Methane dehydro-aromatization over Mo/HZSM-5 in the absence of oxygen : A multinuclear solid-state NMR study of the interaction between supported Mo species and HZSM-5 zeolite with different crystal sizes

A high-resolution solid-state NMR study on nano-structured HZSM-5 zeolite

Mild oxidation of thiophene over TS-1/H2O2

High effective dehydration of bio-ethanol into ethylene over nanoscale HZSM-5 zeolite catalysts

Modification of small-crystal titanium silicalite-1 with organic bases: Recrystallization and catalytic properties in the hydroxylation of phenol