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

Graphene-Like Two-Dimensional Materials

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Large-area MoS(2) atomic layers are synthesized on SiO(2) substrates by chemical vapor deposition using MoO(3) and S powders as the reactants. Optical, microscopic and electrical measurements suggest that the synthetic process leads to the growth of MoS(2) monolayer. The TEM images verify that the synthesized MoS(2) sheets are highly crystalline.

Synthesis of Large‐Area MoS2 Atomic Layers with Chemical Vapor Deposition

Carbon nanotube–polymer composites: Chemistry, processing, mechanical and electrical properties

A new wet chemistry approach, based on low-temperature (360 °C) decomposition in oleylamine of single-source precursors containing both metal and sulfur, is proposed for the production of stable free-standing nanosheets of MoS2 and WS2. The one-pot synthesis permits high-quality 2D nanosheet crystals of MoS2 and WS2 to be obtained with a modular number of nanolayers for units. The layered materials obtained are covered by a dynamic protective coating of oleylamine that stabilizes the suspension, avoids aggregation and oxidation phenomena, and could be easily functionalized with other molecules or nanosystems to introduce new properties to the hybrid organic–inorganic nanocomposite. The reaction products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), attenuated total reflectance Fourier transform infrared spectroscopy (ART-FTIR), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis coupled with mass s...

A Novel Wet Chemistry Approach for the Synthesis of Hybrid 2D Free-Floating Single or Multilayer Nanosheets of MS2@oleylamine (M═Mo, W)

For the applications of photocatalytic processes aimed to the removal of pollutants from wastewater, slurry reactors that employ aqueous suspension of titanium dioxide nanoparticles are not suitable due to the inconvenient and expensive separation of photocatalyst from treated wastewater. To overcome this drawback, the nanosized titanium dioxide needs to be immobilized on a transparent support. In the present paper, recyclable visible-light active N-doped TiO2 photocatalyst was immobilized on glass spheres using a simple sol–gel method. The decrease of N-doped TiO2 crystallites size was obtained with the addition of Triton X-100 as surface-active agent. The effect of sol–gel synthesis temperature was investigated on the crystallization and crystallites size of N-doped TiO2 obtaining that the best temperature for the immobilization through dip-coating process was found at −20 °C. The removal of methylene blue (MB) and eriochrome black-T (EBT) in aqueous solutions was tested to evaluate the photocatalytic activity of the immobilized photocatalyst. The optimization of N-doped TiO2 amount on glass spheres was evaluated using MB as model pollutant. In particular, it was found that until four dip-coating steps, the photocatalytic activity increased. Moreover, the N-doped TiO2 immobilized on glass spheres (NDc) can be easily separated from the reaction mixture, and maintained excellent photocatalytic activity and durability after four cycles. Finally, NDc showed a high photocatalytic activity in the decolorization and mineralization of MB and EBT both under UV and visible light irradiation.

Nanostructured N-doped TiO2 coated on glass spheres for the photocatalytic removal of organic dyes under UV or visible light irradiation

La 1− x Ca x FeO 3 ( x =0.1, 0.2, 0.3, 0.4, 0.5) perovskites prepared by citrate method and calcined at 1073 K have been investigated as catalysts for methane combustion. The formation of the perovskite structure has been shown by X-ray diffraction (XRD) for all samples. The surface area (SA) values are in the range 3–6 m 2  g −1 for the samples up to x =0.4, whereas SA is 0.7 m 2  g −1 for the specimen with x =0.5. The atomic susceptibility increases with increasing in Ca content. The Fe 4+ /Fe total ratio has been determined by both redox titration and TPR analysis. The amount of Fe 4+ enhances with Ca substitution but the Fe 4+ /Ca 2+ ratio is quite constant giving rise to an increasing formation of oxygen vacancies to preserve charge neutrality. All perovskites show a similar intrinsic activity in CH 4 combustion with activation energy, E a , of about 23 kcal mol −1 . A slightly lower value of E a is shown by LaFeO 3 which, in contrast with Ca substituted samples, exhibits a small cationic defectivity. Methane reaction order lower than one was found for all catalysts.

La, Ca and Fe oxide perovskites: preparation, characterization and catalytic properties for methane combustion

Catalytic methane combustion and CO oxidation were investigated over AFeO3 (A=La, Nd, Sm) and LaFe1−xMgxO3 (x=0.1, 0.2, 0.3, 0.4, 0.5) perovskites prepared by citrate method and calcined at 1073 K. The catalysts were characterized by X-ray diffraction (XRD). Redox properties and the content of Fe4+ were derived from temperature programmed reduction (TPR). Specific surface areas (SA) of perovskites were in 2.3–9.7 m2 g−1 range. XRD analysis showed that LaFeO3, NdFeO3, SmFeO3 and LaFe1−xMgxO3 (x·0.3) are single phase perovskite-type oxides. Traces of La2O3, in addition to the perovskite phase, were detected in the LaFe1−xMgxO3 catalysts with x=0.4 and 0.5. TPR gave evidence of the presence in AFeO3 of a very small fraction of Fe4+ which reduces to Fe3+. The fraction of Fe4+ in the LaFe1−xMgxO3 samples increased with increasing magnesium content up to x=0.2, then it remained nearly constant. Catalytic activity tests showed that all samples gave methane and CO complete conversion with 100% selectivity to CO2 below 973 and 773 K, respectively. For the AFeO3 materials the order of activity towards methane combustion is La>Nd>Sm, whereas the activity, per unit SA, of the LaFe1−xMgxO3 catalysts decreases with the amount of Mg at least for the catalysts showing a single perovskite phase (x=0.3). Concerning the CO oxidation, the order of activity for the AFeO3 materials is Nd>La>Sm, while the activity (per unit SA) of the LaFe1−xMgxO3 catalysts decreases at high magnesium content.

Paolo Ciambelli

Papers

A Novel Wet Chemistry Approach for the Synthesis of Hybrid 2D Free-Floating Single or Multilayer Nanosheets of MS2@oleylamine (M═Mo, W)

Nanostructured N-doped TiO2 coated on glass spheres for the photocatalytic removal of organic dyes under UV or visible light irradiation

La, Ca and Fe oxide perovskites: preparation, characterization and catalytic properties for methane combustion

AFeO3 (A=La, Nd, Sm) and LaFe1−xMgxO3 perovskites as methane combustion and CO oxidation catalysts: structural, redox and catalytic properties

Environmental catalysis: trends and outlook