On the Effect of the Strength of Acid Sites in Heterogeneous Catalysts on the Activity in the Skeletal Isomerization of n-Butane

The catalytic activity of three groups of acid catalysts different in the nature and strength of acid sites in the skeletal isomerization of n-butane was studied. It was found that the strength of the sites did not correlate with the rate of the reaction.     

WO3/MO2 (M = Zr, Sn, Ti) heterogeneous acid catalysts: Synthesis, study, and use in cumene hydroperoxide decomposition

Thirty (5–40)% WO₃/MO₂ (M = Zr, Ti, Sn), heterogeneous acidic catalysts have been synthesized by two methods, specifically, via homogeneous acid solutions and from solutions brought to pH 9 with ammonia, both followed by calcination at 600–900°C. The catalysts have been characterized by IR spectroscopy and scanning electron microscopy, and their aqueous washings have been analyzed. Their acidity has been determined by the thermal analysis of samples containing adsorbed pyridine, and in terms of the proton affinity scale. Catalytic activities have been compared for cumene hydroperoxide (CHP) decomposition at 40°C in cumene and acetone. For all M, the catalysts are one type and contain W in strongly and weakly bound states, the latter being a polyoxometalate that can be washed off. Both tungstate phases are active in acid catalysis. Brønsted acid sites with a broad strength distribution have been found. The strongest of them are heteropolyacid protons. The catalysts 30% WO₃/SnO₂ and 20% WO₃/ZrO₂ (in acetone) and 10–20% WO₃/TiO₂ (in cumene) are the most active in CHP decomposition, and their activity is not related to their total acidity. Phases containing W⁶⁺ that form during the high-temperature synthesis are responsible for the high acidity, and additional protons that may appear owing to W⁶⁺ reduction can play only a minor role.     

Thiophene conversion in the BIMF process

Catalytic conversion of an oil distillate with the added extra amounts of thiophene over a zeolite catalyst was studied. The rate of the catalyst deactivation was found to increase with the increase in the thiophene concentration in the feed. A possible pathway of the thiophene conversion is discussed.     

Role of carbonate-carboxylate species during alumina coking

The role of carbonate-carboxylate species on alumina surface has been studied during alumina coking. The species are intermediates poisoning the active sites. Little O₂ added to the hydrocarbon feedstock causes further oxidation of the species and promotion of the active sites.     

Sorption of carbon dioxide by the composite sorbent “potassium carbonate in porous matrix”

Sorption of CO₂ in the presence of water vapor by the K₂CO₃—-Al₂O₃ composite sorbent was studied by IR spectroscopy in situ, X-ray diffraction analysis, and the differentiating dissolution method and reasons for a decrease in its dynamic capacity are given. The samples containing K₂CO₃·1.5H₂O in pores are characterized by the maximal dynamic capacity. A mechanism for CO₂ sorption was proposed, which qualitatively explains the obtained dependence of the capacity on the water content in the composite sorbent. A high dynamic capacity can be maintained by regeneration of the sorbents by water vapor at 170 °N. The capacity of the sorbents decreases during the first 10 sorption—regeneration cycles due to the formation of an inactive phase of potassium aluminum carbonate.     

Abnormally high fractal dimension of silica surfaces measured by adsorption of aliphatic alcohols

Factors leading to abnormally high fractal dimension D of silica surfaces measured by adsorption of aliphatic alcohols have been analyzed. , D .     

Adsorption of H3PW12O40 by porous carbon materials

Adsorption of H₃PW₁₂O₄₀ from water and organic oxygen-containing solvents (AcOH, Me₂CO, MeOH) by carbon mesoporous materials, viz., Sibunit and catalytic filamentous carbons (CFC), was studied. The amount of irreversibly sorbed heteropolyacid is 50—100 mg g^–1 of support and decreases in the series of solvents: H₂O > Me₂CO > AcOH > MeOH. The adsorption capacity of CFC depends on the specific surface, total pore volume, and microstructure of the CFC fiber.     

Deamination of butylamines on the surface of acidic oxide catalysts

Studies of the deamination of tert-, sec- and n-butylamines on several silicate and phosphate catalysts at 543–704 K have revealed that the reaction proceeds only with the participation of protonic cneters, its rate is independent of the strength of acidic centers and affected only by the amine structure. Butylammonium ion conversion is suggested to be the rate-determining step.

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Acid properties of ZSM-5 zeolites after hydrothermal treatment at 540°C

Acid properties of ZSM zeolites have been studied under various conditions of hydrothermal treatment. It is shown that with increasing , the concentration of proton centers monotonically decreases and variations in the concentration of Lewis acid centers is of extremal character.

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The Effect of Modification on the Structural,Acidic, and Catalytic Properties of a Layered Aluminosilicate

The effect of modification on the structural, acidic, and catalytic properties of a natural layered aluminosilicate containing 90% montmorillonite was studied. With the use of low-temperature nitrogen adsorption and XRD analysis, it was found that the addition of hydroxo complexes of aluminum prevents the silicate layers of the layered aluminosilicate from closing upon heating and results both in the formation of stable micropores and in a considerable increase in the specific surface area. The acidic properties of the H, Na, and Al forms of the layered aluminosilicate were studied by IR spectroscopy of adsorbed CO molecules and by the indicator method. After modification with hydroxo complexes of aluminum, the number of Lewis acid sites and the accessibility of acidic OH groups to CO adsorption increased. The total number and strength of acid sites increased as the calcination temperature of the layered aluminosilicate was increased. A correlation between catalytic activity in the reaction of acetone dimerization and the number of acid sites in different forms of the layered aluminosilicate was obtained.