Ryszard Fiedorow

Catalytic activity of supported heteropoly acids for reactions requiring strong acid centres

The effect of supports such as silica, alumina, amorphous aluminosilicate and magnesia on the activity of heteropoly acids (HPA) for reactions requiring strong and very strong acid sites has been studied. It has been found that 12-tungstophosphoric acid (HPW) mounted on alumina and silica catalyses cumene cracking at 150 °C, with conversion ca. 90%, and toluene disproportionation at temperatures as low as 250 °C. The catalytic performance increased with increasing HPA content and reached its maximum in the loading range 38–50 wt.%. With > 38 wt.% HPW on silica and > 60 wt.% HPW on γ-alumina the supported HPW catalysts showed catalytic activity for low-temperature isomerisation of hexane as did unsupported HPW. Activity for the latter reaction indicates the presence of very strong acid centres with acid strength approaching that of superacids. No activity for the reactions studied was found for magnesia-supported HPW.

The influence of acid-base properties of oxide supports on platinum dispersion during oxygen treatments

Abstract The role of acid and base properties of oxide supports on the stability of Pt on these supports during oxygen treatment at 550 °C was investigated. The acid-base properties were determined by the indicator-titration method. The supports studied were γ-alumina, silica, silica-alumina, magnesia, and silicalite; the Pt was introduced to these supports by impregnation with H 2 PtCl 6 or Pt(C 5 H 7 O 2 ) 2 . The introduction of Pt did not significantly affect the acid-base properties. Hydrogen chemisorption and X-ray diffraction were used to determine the changes in Pt dispersion that occurred due to O 2 treatments. It was observed that O 2 treatments at 550 °C of Pt on supports with basic sites (γ-Al 2 O 3 and MgO) resulted in increases in Pt dispersions, while decreases in Pt dispersion occurred for Pt supported on acidic and neutral supports (silica-alumina, silica, and silicalite).

Copolymerization of ethylene and 1-butene using A Cr-silica catalyst in a slurry reactor

A novel slurry reactor was used to investigate the copolymerization behavior of ethylene and 1-butene in the presence of 1 wt % Cr on Davison silica (Phillips-type) catalyst over the temperature range of 0–50°C, space velocity of about 0.0051 [m3 (STP)]/(g of catalyst) h, and a fixed ethylene to 1-butene feed mole ratio of 95 : 5. The effect of varying the ethylene to 1-butene feed ratios, 100 : 0, 96.5 : 3.5, 95 : 5, 93 : 7, 90 : 10, 80 : 20, and 0 : 100 mol/mol at 50°C was also studied. The addition of 1-butene to ethylene typically increased both copolymerization rates and yields relative to ethylene homopolymerization with the same catalyst, reaching a maximum yield for an ethylene: 1-butene feed ratio of 95 : 5 at 50°C. The incorporation of 1-butene within the copolymer in all cases was less than 5 mol %. The average activation energy for the apparent reaction rate constant, ka, based on total comonomer mole fraction in the slurry liquid for the ethylene to 1-butene feed mole ratio of 95 : 5 in the temperature range of 50–30°C measured 54.2 kJ/mol. The behavior for temperatures between 30 to 0°C differed with an activation energy of 98.2 kJ/mol; thus, some diffusion limitation likely influences the copolymerization rates at temperatures above 30°C. A kinetics analysis of the experimental data at 50°C for different ethylene to 1-butene feed ratios gave the values of the reactivity ratios, r1 = 27.3 ± 3.6 and r2 ≅ 0, for ethylene and 1-butene, respectively.

Ammoxidation of Toluene on Coke-Covered Alumina

Abstract The catalytic activity of coke formed during the ammoxidation of toluene was studied as a function of time-on-stream. The changes in catalytic activity could be explained in terms of competing rates of formation of active centres (coke) and of their encapsulation within the growing coke mass. The acid strength of coke-forming centres on alumina, the concentration of paramagnetic centres in the coke and the elemental composition of the coke were examined and related to the nature of the ammoxidation process. Some of the chemical character of the coke was evaluated using IR spectrophotometry.

Thermal stability of hybrid materials based on epoxy functional (poly)siloxanes

Epoxy functional (poly)siloxanes are one of the most important classes of modified silicones. Due to high reactivity of epoxy group and specific features of siloxane chain, they can make an excellent raw material for synthesis of hybrid materials. Results obtained in this study have shown that both the modification of epoxy resins with epoxy functional disiloxanes as well as the application of polysiloxanes with long polysiloxane chains and a specified content of epoxy groups makes it possible to produce hybrid materials of very good thermal stability. Crosslinking reactions were carried out with use of four diamines of which the best one appeared to be 4,4′-diaminodiphenylmethane. The highest thermal stability was found in the case of hybrid materials obtained from epoxy functional polysiloxanes.

Studies of the Surface of Fluorinated Carbon in the Aspect of its Catalytic Properties

Abstract Surface properties of fluorinated carbon were characterised from the point of view of its use as a material for catalytic purposes. Samples with different fluorine content (from 10 to 65 wt.%) were tested for their catalytic activity for a number of reactions of acid-base catalysis involving residual hydroxyl groups as active centres. It was found that they were capable of catalysing only such a reaction proceeding through the formation of carbenium ion for which the presence of very weak acid centres is sufficient. The generation of only weak acidity as a result of fluorination was unexpected, therefore calculations were performed using AM1 method to explain this fact. A simple molecule used as a model of fluorinated carbon surface enabled to predict acidity of residual OH groups which was in agreement with experimental findings.

Determination of the Rate Constants from Phase Delay Effect in Chemical Reactions

AbstractA new method for the determination of rate constant k of a reaction of the type A + X → P1 + P2 is presented. The method is based on the phase delay between the oscillatory inflow of the parent substance X into the reaction medium and the concentration of the parent substance in the field changing as a result of the reaction, which can be expressed as tan φ =

Hydrosilylation on Hydrophobic Material-Supported Platinum Catalysts

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