Catalysts Based on Fiberglass Support: IV. Platinum Catalysts Based on Fiberglass Support in Oxidation of Hydrocarbons (Propane and n-Butane) and Sulfur Dioxide

Platinum catalysts (0.003–0.52% Pt) based on leached sodium silicate and boron silicate fiberglass supports are studied in the complete oxidation of hydrocarbons (n-butane and propane) and high-temperature SO₂ oxidation. It was shown that platinum localized in the bulk of the glass matrix show a higher activity and thermal stability than metal particles supported on the outer surface of fiberglass. The experimental results for hydrocarbon oxidation on platinum-containing fiberglass gauzes at short contact times are discussed.     

Effect of thermal treatment conditions on the acid properties of zeolite Beta

The acid properties of zeolite Beta were studied by IR spectroscopy with the use of adsorbed NH₃ and CO probe molecules. It was found that the strength of the Brønsted acid sites (BASs) of zeolite Beta was the same as that of zeolite ZSM-5. Approximately a third of the total amount of BASs participated in the formation of hydrogen bonds at interdomain boundaries; thus, they were inaccessible to molecules larger than the ammonia molecule. The qualitative and quantitative compositions of acid sites in zeolite Beta can be regulated by changing the conditions of calcination of the initial zeolite form (temperature and/or gas atmosphere). Calcination under vacuum conditions afforded the highest acidity of the zeolite with respect to all types of acid sites. Calcination in a flow of air resulted in the lowest acidity of the sample, especially, with respect to the concentration of strong Lewis acid sites, because of the formation of an alumina phase. Calcination in an atmosphere of helium resulted in a decrease (as compared with a vacuum) in the rate of removal of the organic template decomposition products of the initial zeolite form from the channel volume. The resulting ethylene was mainly adsorbed at strong Lewis sites and converted into undesorbed condensation products.     

Isotope exchange between NO and H2O on a platinum-containing catalyst based on fiberglass

The dynamics of ¹⁸O isotope exchange between NO or H₂O and a catalyst and the dynamics of ¹⁸O label transfer from NO to H₂O have been studied under conditions of sorption-desorption equilibrium. The occurrence of a reaction of oxygen exchange between NO and water sorbed in the bulk of the catalyst was detected. This reaction occurs at platinum sites with the participation of acid sites of the glass matrix. The rate constants of the reaction of NO with platinum sites and the diffusion coefficients of water in the bulk of the glass matrix are evaluated.     

Catalysts Based on Fiberglass Supports: V. Absorption and Catalytic Properties of Palladium Catalysts Based on a Leached Silica-Fiberglass Support in the Selective Hydrogenation of an Ethylene–Acetylene Mixture

The absorption and catalytic properties of palladium catalysts (0.01% Pd) based on leached soda–silica fiberglass supports were studied in the selective hydrogenation of acetylene as the constituent of an ethylene–acetylene mixture. It was found that fiberglass catalysts exhibited much higher selectivity than traditional supported Pd catalysts. It was suggested that the high selectivity in the reaction of acetylene hydrogenation resulted from the selective absorption (diffusion) of acetylene in the bulk of fiberglass, where Pd microparticles are localized.     

2H Solid-State NMR Spectroscopy Reveals the Dynamics of a Pyridine Probe Interacting with Coordinatively Unsaturated Metal Sites of MIL-100(Al) Metal–Organic Frameworks

Coordinatively unsaturated metal sites (CUS) play an important role in catalysis by metal-organic frameworks (MOF). Being an intrinsic part of the framework the CUS take the role of acidic sites active in industrially relevant processes such as condensation or oxidation reactions. The key step of such reactions represents the coordination of the reagents to CUS. In MOFs the mechanism of the reagent interaction with CUS is poorly understood. Herein, we characterize the interaction of a widely used acidity probe pyridine with CUS of MIL-100(Al) MOF by means of the ²H solid-state NMR spectroscopy. ²H NMR reveals that pyridine species, which are interacting with CUS and the ones which are coordinated to the Al−OH site, exhibit different motional behavior. ²H NMR line shape as well as T₁, T₂ relaxation analyses for [D₅]pyridine adsorbed in MIL-100(Al) allowed us to perform a detailed characterization of pyridine dynamics in both states including the kinetics of the exchange process between these adsorption states.     

A study of microporous aluminophosphates obtained in the presence of symmetrical di-n-alkylamines

Microporous aluminophosphates and silicoaluminophosphates were obtained by hydrothermal synthesis with a number of symmetrical di-n-alkylamines as templates. The influence of the reagents and chemical composition of the starting reaction gel on the phase composition of the products obtained was studied. Pure ATO-type crystals were formed when the organic component was abundant in the reaction mixture and aluminum isopropoxide served as an aluminum source. Various physicochemical investigations revealed that the properties of the products obtained depend on the amine nature.     

Reaction of Some Terpenoids with Malononitrile in the Presence of Hydrotalcite

α-Ionone and 5,5,8-trimethyl-3,7-nonadien-2-one react with malononitrile in the presence of specially prepared hydrotalcite to afford the corresponding Knoevenagel condensation products with high yield and selectivity.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 6, 2005, pp. 859–863.Original Russian Text Copyright © 2005 by Khomenko, Volcho, Toktarev, Echevskii, Salakhutdinov, Barkhash.     

Effect of zeolite matrix structure on the stabilization of silver clusters

Silver clusters characterized by an absorption band at 320–340 nm are found to be easily stabilized by zeolites of mordenite type. Size of the clusters is discussed on the basis of results on introducing silver clusters into the zeolites with various channel diameters and on electron microscopy and low-angle X-ray scattering (LAXS) data.     

N<Subscript>2</Subscript> and CO as probe molecules for determining the properties of acid sites on the surface of zeolites

The applicability of molecular nitrogen as a probe for the Brønsted and Lewis acid sites of HNaY and HZSM-5 zeolites was studied by Fourier transform IR spectroscopy. The integrated absorption coefficients of bands due to N—N vibrations in complexes with Brønsted and Lewis acid sites were determined. The correlation between the integrated absorption coefficients and the positions of bands due to N—N vibrations in nitrogen interacting with the acid sites of test samples is discussed. We propose using the low-temperature adsorption of nitrogen for express determination of the concentrations of strong Lewis and Brønsted acid sites in zeolites.Translated from Kinetika i Kataliz, Vol. 46, No. 1, 2005, pp. 108–114.Original Russian Text Copyright © 2005 by Malyshev, Paukshtis, Malysheva, Toktarev, Vostrikova.