Catalysts Based on Fiberglass Supports: II. Physicochemical Properties of Alumina Borosilicate Fiberglass Supports

The properties of borosilicate fiberglass supports were studied using a set of physicochemical techniques (BET; transmission electron microscopy; IR spectroscopy; and ¹¹B, ²³Na, ²⁷Al, and ²⁹Si NMR spectroscopy). Unleached fiberglass was characterized by the presence of silicon primarily in the Q ²form (two silicon atoms in the second coordination sphere of silicon–oxygen tetrahedrons) and by a comparatively homogeneous distribution of concomitant heteroatoms (B, Al, and Na). Under the action of an acid, the extraction of nonsilica components and the rearrangement of a silicon–oxygen framework (the transition of Q ²to Q ³+ Q ⁴) took place simultaneously. This was accompanied by the development of the surface and by the formation of channels with a wide range of sizes: from channels 15–50 Å in diameter (the adsorption properties of these channels are similar to those of mesopores in ordinary silica supports) to microchannels, which are typical of pseudolayer intercalation structures described previously for leached soda–silica fiberglass.     

Structural properties and state of the surface layer of zirconium dioxide modified by tungstate anions

A tetragonal metastable phase of zirconium dioxide formed after the addition of tungstate anions (>13 mol %) to the hydroxide precursor by different methods with heating (600–700°C), as revealed by X-ray diffraction analysis and X-ray photoelectron and IR spectroscopy. The W⁶⁺ and W⁵⁺ cations formed a solid solution with ZrO₂. On the surface of the solid solution, the tungsten cations formed tungstate clusters (?WO _x ?)n. The formation of the WO₃ phase was observed at concentrations of tungstate anions higher than 17.6 mol % or at temperatures of 850–870°C.     

Acid-base properties of alumina prepared from a hydrated product of centrifugal thermal activation of hydrargillite (cta-product)

Summary Acid-base properties of aluminas prepared by thermal treatment of a hydrated CTA-product at 600°C were studied. The CTA-oxides, representing γ-Al₂O₃, were shown to contain terminal and bridged OH-groups. The concentration of the terminal OH-groups in the CTA-oxides was found to exceed their concentration in γ-Al₂O₃ prepared by dehydration of the “precipitated” pseudoboehmite, whereas the concentration of the bridged OH-groups in the CTA-oxides was lower than that in γ-Al₂O₃ prepared from pseudoboehmite. The total concentration of the surface Lewis acid sites in CTA-oxides varies within the limits of 2.80-4.14 mmol/m² and is essentially above that in g-Al₂O₃ (2.25 mmol/m²). The distinctive feature of the CTA-oxides is that their surface contains strong Lewis acid sites with n_CO = 2220 and 2238 cm^-1. The total concentration of basic sites in the CTA-oxides is lower than that in g-Al₂O₃, however, in contrast to g-Al₂O₃,they contain strong basic sites with n_CDCl3 = 2200 cm^-1.     

IR studies of the transformations of nitrogen-containing organic intermediates during selective reduction of nitrogen oxides by hydrocarbons

Thermal transformations of nitromethane and deuterated acetonitrile adsorbed on the surface of H-ZSM-5, Cu-ZSM-5, Co-ZSM-5 has been studied by IR spectroscopy. The nature of cation has been found to greatly affect the transformation pathways of these species as possible intermediates in the NO_x selective reduction by hydrocarbons, thus explaining the different selectivities of these catalysts.     

Study of the factors affecting the formation of copper–chromium/aluminum oxide compounds with a spinel structure

The effect of the Cr³⁺/Al³⁺ ratio on the crystallization temperature of mixed oxide compounds with a spinel structure and their structural features and morphological characteristics have been studied using a combination of physicochemical methods: thermal analysis, IR spectroscopy, X-ray powder diffraction, and electron microscopy. The role of temperature of synthesis and drying of Cu–Cr/Al hydroxy precursors in the formation of copper-containing spinels CuCr _x Al_2–x O₄, where x = 0–2, has been elucidated. The results are of interest for selection of the optimal composition and conditions of synthesis and formation of copper-containing spinels for their practical use.     

Surface acidic sites of highly disperse magnesium chloride: IR and ESR spectroscopy studies

Experimental data obtained by means of some high performance techniques allow to identify and register quantitatively the Lewis acidic sites on the surface of highly disperse magnesium chloride. Carbon monoxide adsorption on magnesium chloride has been studied with the IR diffuse reflectance spectroscopy (IRS-DR). The interaction of some stable nitroxyl radicals with magnesium chloride has been investigated with the ESR technique.     

Real structure of metastable forms of aluminum oxide

Differences in the real structure of γ-Al₂O₃ samples obtained by the thermal decomposition of pseudoboehmite and boehmite prepared by the hydrothermal treatment of bayerite were found. The transformations of these structures during their conversion to δ-Al₂O₃ as the treatment temperature increased were studied. The rate of conversion of metastable alumina species into the stable α-Al₂O₃ phase significantly depends on the real structure of samples. The rate of this transformation is drastically retarded in the presence of extended defects in the oxides originated from boehmite, and the stability of metastable alumina species increased as the degree of surface dehydroxylation increased.     

Study of <Emphasis Type="Italic">n</Emphasis>-hexane isomerization on Pt/SO<Subscript>4</Subscript>/ZrO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts: Effect of the state of platinum on catalytic and adsorption properties

The state of surface Pt atoms in the Pt/SO₄/ZrO₂/Al₂O₃ catalyst and the effect of the state of platinum on its adsorption and catalytic properties in the reaction of n-hexane isomerization were studied. The Pt-X/Al₂O₃ alumina-platinum catalysts modified with various halogens (X = Br, Cl, and F) and their mechanical mixtures with the SO₄/ZrO₂/Al₂O₃ superacid catalyst were used in this study. With the use of IR spectroscopy (CO_ads), oxygen chemisorption, and oxygen-hydrogen titration, it was found that ionic platinum species were present on the reduced form of the catalysts. These species can adsorb to three hydrogen atoms per each surface platinum atom. The specific properties of ionic platinum manifested themselves in the formation of a hydride form of adsorbed hydrogen. It is believed that the catalytic activity and operational stability of the superacid system based on sulfated zirconium dioxide were due to the participation of ionic and metallic platinum in the activation of hydrogen for the reaction of n-hexane isomerization.     

Effects of the modification of reforming alumina-platinum catalysts with zirconium

The effects of the modification of supported platinum as a constituent of reforming Pt/Al₂O₃ and Pt-Re/Al₂O₃ catalysts by introducing zirconium, which was obtained from various starting compounds, into the composition of the support were studied. These effects were most pronounced if difficult-to-hydrolyze compounds served as a source of zirconium. It was found that zirconium affected the metal-support interaction strength, which is responsible for the formation of the most strongly adsorbed hydrogen species (over the temperature range of 300–500°C). This suggests a change in the electronic state of platinum under the action of zirconium. Platinum sites became more regular; as a result of this, the reaction rate parameters of heptane conversion changed.