Yuri Kalvachev

Selective partial oxidation of propylene to propylene oxide on Au/Ti-MCM catalysts in the presence of hydrogen and oxygen

Publisher Summary There exist typical characteristics features in the reaction of propylene with hydrogen and oxygen over Au/Ti-MCM catalysts. These are an increase of propylene oxide (PO) yield over 2–3 hours (at 323 K) and 70–90 min (at 373 K), followed by a period of relative stability, increasing PO selectivity, and decreasing hydrogen consumption as a function of time; PO selectivity decreases with increasing the amount of titanium in the catalysts. In all these cases, the conversion of hydrogen is high (10%–50%). This chapter discusses the catalytic activity of gold deposited on titanium-containing mobil crystalline material (MCM)-41 for the partial oxidation of propylene to PO in the presence of oxygen and hydrogen. In the present report, the influence of the amount of titanium in Ti-MCM-41 and gold loading over this reaction is explained in the chapter. The results show that the optimum temperature for selective partial oxidation of propylene to propylene oxide is about 100°C. With increasing temperature, the conversion of propylene increased, but PO selectivity was then lower. The conversion of propylene on these catalysts is about 1%–2 %, while the conversion of hydrogen, in all cases, is high. Probably the oxidation of propylene occurs at the perimeter interface between gold and the support, whereas hydrogen is activated on the surface of the gold particles.

Alcohol Reactivity on Zeolites and Molecular Sieves

Abstract Zeolites and molecular sieves have been extensively studied and applied in different fields. Their specific crystalline structure and composition make it possible to obtain high-activity stable catalyst systems for a wide range of chemical reactions. There are many investigations on the structural characteristics and adsorption and catalytic properties of zeolites and molecular sieves as well as on the relation between the different properties. The nature of active sites in zeolite catalysts and the mechanism of catalytic processes on their surface belong to the most important problems of the investigations.

Preparation and characterization of new polyimide films containing zeolite L and/or silica

New polyimide (PI) films containing zeolite L and/or silica, having a thickness of tens of micrometers, were prepared using a PI matrix with pendant carboxylic groups. The influence of various ratios of inorganic filler on thermal stability, dielectric behavior, and gas transport properties of the films was studied with respect to their structure. The surface morphology was investigated by scanning electron microscopy. The films were flexible, tough, and showed good thermal properties with a glass transition temperature in the range of 187–218°C. The dielectric spectroscopy revealed γ and β subglass transitions having the corresponding relaxation activation energy in the range of 44.7–51.4 kJ mol−1 and 65.1–121.6 kJ mol−1, respectively. At temperatures above 200°C, a conductivity relaxation process was evidenced. Gas permeation tests using small molecules (O2, N2 and CO2), at 6 atm and 30°C, indicated that the PI films containing higher amount of zeolite showed the highest permeability for all gases.

Electromechanical properties of polyimide composites containing titanium dioxide nanotubes

Polyimide composite films were prepared by casting solutions resulting from direct mixing of a poly(amic acid) and titanium dioxide (TiO2) nanotubes (TNTs) onto glass plates, followed by thermal imidization. TNTs with outer diameters of approximately 10–12 nm and length of several hundreds of nanometers were synthesized by the hydrothermal method. The morphology of the nanotubes was investigated by using high-resolution transmission electron microscopy. The influence of TNTs content on structural, thermal, and electromechanical properties of pure polyimide and composite films was studied. The scanning electron microscopy and atomic force microscopy showed good compatibility between TNTs filler and polyimide matrix. The value of average roughness of film surface increases with increasing the content of TNTs. The films were flexible, tough, and exhibited high thermal stability. A study of microelectromechanical properties of these films was performed. The films showed nanometric displacements in the range of 250–800 nm when an electric voltage of 500 V was applied on their surface.

Synthetic Micro- and Nanocrystalline Zeolites for Environmental Protection Systems

Coal combustion ash with a 2.25 ratio of SiO2/Al2O3 was used to synthesize an X-type zeolite by alkaline fusion followed by hydrothermal treatment. The reaction products were investigated for phase identification by X-ray diffraction analysis. The surface morphology and the elemental composition were determined by scanning electron microscopy with an energy-dispersive X-ray analyzer. The vibrations of the structural units in the zeolite framework were revealed by IR spectroscopy. Zeolite X obtained from pure initial materials was used as a reference sample for comparison. The results confirmed the conversion of coal ash into a zeolite possessing a dominant Na-X phase of micro- or nanocrsystalline morphology depending on the synthesis conditions. The coal ash Na-X zeolite was studied for adsorption of carbon dioxide under static conditions.

Infrared study of cyclohexanol chemisorption in SAPO molecular sieves

The infrared spectra of cyclohexanol adsorbed on SAPO molecular sieves (four SAPO-5 samples with different SiO2 contents, SAPO-11 and SAPO-31 were studied) show bands due to cyclohexanone (1732 cm–1) at room temperature, while on heating cyclohexene is formed. The results are discussed in terms of the existence of basic sites parallel to the Bronsted acid sites.

Fluoride etching of mordenite and its influence on catalytic activity

Due to its structure and high Si/Al ratio, zeolite mordenite has high thermal and acidic stability. Mordenite-type of zeolites have been used as catalysts in many industrially important reactions such as hydrocracking, hydroisomerization, alkylation, acid-catalyzed isomerization of alkanes and aromatics, reforming. In order to overcome the problem of the limited access to the active sites, OSDA-free synthesized mordenite undergoes fluoride etching as a post-synthetic treatment. The post-synthetic treatment is performed with hydrofluoric acid in combination with ammonium fluoride. Thus, the porosity is enhanced additionally without changing considerably the Si/Al ratio of the zeolite framework. All samples have been characterized by X-ray diffraction analysis, nitrogen adsorption, scanning electron microscopy, high-resolution transmission electron microscopy and solid-state nuclear magnetic resonance spectroscopy. The catalytic activity of the samples obtained has been investigated in the reaction of m-xylene transformation. All mordenite samples having undergone post-synthetic treatment exhibit catalytic activity higher than that of the parent sample.

Influence of the preparation method of sulfated zirconia nanoparticles for levulinic acid esterification

Zirconia nanomaterials were prepared by hydrothermal synthesis with or without template and were modified by post synthesis method with sulfate groups. The materials were thoroughly characterized by X-ray powder diffraction, TEM, N2 physisorption, FTIR spectroscopy of adsorbed pyridine TG analysis and XPS spectroscopy. The catalytic performance of nanosized ZrO2 catalysts and their sulfated modifications was studied in levulinic acid esterification with ethanol. The sulfate group’s dispersion was predetermined by the use of template during the mesoporous zirconia synthesis. A relation between sulfate groups leaching and the applied synthesis conditions (with or without template) of the zirconia nanoparticles was found. Sulfated materials showed significantly higher activity compared to non-sulfated ones. Furthermore, it has been found that the presence of template during the mesoporous ZrO2 nanoparticles preparation influences significantly the zirconia phase and catalytic performance in levulinic acid esterification.