Milan Hronec

Direct synthesis of phenol from benzene over hydroxyapatite catalysts

Abstract The direct synthesis of phenol from benzene in the gas phase was studied over hydroxyapatite catalysts. The reaction was carried out in a fixed-bed reactor at atmospheric pressure and reaction temperature of 450°C in the presence of ammonia. A high selectivity (about 97%) of phenol formation at about 3.5% conversion of benzene was achieved over catalysts containing Ca and Cu ions in the cation part of hydroxyapatite. Besides phenol as the main reaction product, aniline is also formed. The reaction mechanism involves formation of N2O from NH3 in the first step of reaction. Benzene is oxidized by active oxygen species which are formed on the catalyst by decomposition of N2O.

Hydrogenation of benzene to cyclohexene over polymer-supported ruthenium catalysts

Abstract Partial liquid-phase hydrogenation of benzene to cyclohexene over ruthenium catalysts supported on charcoal and anionic cross-linked polymers is described. The influence of the polarity of polymeric supports, nature of the solvent and the presence of zinc additives on the performance of the catalyst in a glass-lined reactor at 100–110°C and a pressure of 1.5 MPa have been studied. It has been found that at 42–47% conversion of benzene, the selectivity to cyclohexene, observed in water with Ru catalysts supported on a strongly hydrophilic microporous resin, is higher than that displayed by Ru supported on charcoal. The effect of water on the performance of the catalyst is probably a result of formation of a suitable environment around Ru particles and of a good accessibility of metal particles dispersed within the hydrophilic polymer support.

Microporous poly-N,N-dimethylacrylamide-p-styrylsulfonate-methylene bis(acrylamide): a promising support for metal catalysis

Abstract The synthesis of poly- N,N -dimethylacrylamide- p -styrylsulfonate (DMAA-SS) with 4 mol% of methylene bis(acrylamide) mol% of methylene bis(acrylamide) (MBAA) as crosslinker is described. Bulk polymerization of water solution of monomers (DMAA, SS sodium salt, MBAA) was carried out under gamma irradiation. Swellability in water and various organic solvents showed mainly hydrophilic character of the resin. The ion-exchange experiments with 1 M hydrochloric acid and with [Pd(NH 3 ) 4 ] 2+ showed very good accessibility of the inner space of the material. Polymer supported [Pd(NH 3 4 ] 2+ was reduced by hydrogen in methanol, sodium borohydride in water and sodium borohydride in ethanol. Under these last conditions uniform distribution of Pd throughout the resin particles was observed. The activated material turned out to be a good catalyst for the hydrogenation of p -nitrotoluene to p -toluidine in methanol under ambient conditions.

Competitive oxidation of alcohols in aqueous phase using Pd/C catalyst

Abstract A variety of aromatic and aliphatic alcohols and cyclohexanols were oxidized in the aqueous phase, both individually and competitively in pairs, over a carbon-supported palladium catalyst, or the same catalyst modified by Co and Cd as additives. Some of these alcohols were unreactive or less reactive individually, but more reactive in competition. These findings were explained in terms of the interaction of the substrate with oxygen-covered metal catalyst, which depends on the dissociation ability of the alcohols. The promoting effect of Co and Cd additives on the Pd catalyst was also based on the concept of metal-substrate interaction.

Relationships between physico-chemical properties and catalytic activity of polymer-supported palladium catalysts.: Part I. Experimental investigations

Abstract Polymer-supported palladium catalysts based on microporouspolydimethylacrylamide- p -styryl-sulphonate-methylenebis(acrylamide) with 4 and 8% m/m crosslinking degree and various metal contents were prepared. The influence of the crosslinking degree on the metal distribution and on the final activity of the catalyst was studied by a combination of diverse physico-chemical techniques like X-ray microprobe analysis, inverse steric exclusion chromatography, powder X-ray diffraction, electron spin resonance, and catalytic tests.

Relationships between physico-chemical properties and catalytic activity of polymer-supported palladium catalysts II. Mathematical model

Abstract A mathematical model including external mass transport, diffusion in the particle and chemical reaction inside the particle was developed to describe a hydrogenation process in an isothermal batchwise system with a polymer-supported metal catalyst. Various types of reaction kinetics were implemented into the model, e.g., the power law or the Langmuir-Hinshelwood type. The validity of the model was tested on data obtained from the hydrogenation of a 1 M methanol solution of cyclohexene at 25°C and 0.5–1.5 MPa. Diffusional coefficients inside the catalyst, the hydrogenation rate constant and the adsorption constant of hydrogen were estimated. The best model proved to be the model considering the dissociation of hydrogen and neglecting the adsorption terms in the denominator of the Langmuir-Hinshelwood kinetics. Using polymer supports of different swellability, a linear correlation between the logarithm of the diffusional coefficient of a solute inside the polymer and the reciprocal of the swelling volume of the polymer support was derived from ESR measurements. A comparison with values of diffusional coefficients obtained from catalytic tests confirmed the validity of this correlation.

Selective alkylation of biphenyl with t-butanol over large pore zeolites

Abstract Alkylation of biphenyl with t -butanol under liquid phase conditions has been studied over HY and Hβ zeolites with different silicon to aluminum molar ratios as catalysts. HY zeolites have been shown to be more active than Hβ zeolites. A maximum of 58% for the biphenyl conversion has been obtained over HY (15) zeolite at 160°C. The initial catalytic activity of studied zeolites for t -butylation of biphenyl at 160°C can be set in the next order: HY (15)>HY (30)>Hβ (12.5)≅Hβ (25). Both types of zeolites showed a significant selectivity of the monoalkylation step versus di- and polyalkylation with a very high selectivity leading to the 4- t -butylbiphenyl derivative (4-TBB) (near 95% for HY and 87% for Hβ). Moreover, a high initial selectivity in 4,4′-di( t -butyl)biphenyl (4,4′-DTBB) was obtained (near 82% for HY and 90% for Hβ at 160°C). Such a selectivity remained constant with time over HY, while it dramatically decreased over Hβ. Higher temperatures and higher catalyst concentration led to an increase of secondary reactions, which have been evidenced as isomerization of 4-TBB to 3-TBB, 4,4′-DTBB to 3,4′- and 3,3′-DTBB, oligomerization of isobutylene, alkylation of biphenyl with oligomers to higher alkyl- and polyalkylbiphenyls together with disproportionation and transalkylation of alkylbiphenyls.

The use of phase-transfer catalysis for the initiation of p-xylene oxidation

Quaternary onium salts act as phase-transfer agents for Br− and cobalt complexes during cobalt bromide catalyzed oxidation of p-xylene with molecular oxygen in p-xylene-water system.AbstractВ реакции окисления п-ксилола молекулярным кислородом в присутствии воды и катаиизатора-бромистого кобальта использовались липофильные четвертичные катионы в виде межфазных катализаторов для транспорта аниона Br− и комплексных соединений кобальта.

Oxidation of benzoic acid to phenol in the vapor phase. I: Mechanistic aspects

Abstract The vapor-phase oxidation of benzoic acid to phenol over copper catalyst supported on alumina has similar features to those described for the homogeneous system. The mechanism of reaction involves cupric benzoate as the principal intermediate and the rate of its formation on the catalyst surface is the rate-determining step. Molecular oxygen reoxidizes the reduced copper species of catalyst. No oxidation of phenol occurs on the catalyst in an inert atmosphere. The oxidation of benzoic acid in the presence of optimal concentration of oxygen and water follows a first-order rate equation with the rate constant k = 0.124 ± 0.014 hr −1 at 285 °C and the apparent activation energy 63.0 ± 4.5 kJ mol −1 .

Oxidation of cyclohexylamine by air to its oxime

Abstract The oxidation of cyclohexylamine was studied over tungsten, molybdenum and vanadium oxides containing catalysts supported on silica, γ-alumina or hydrotalcite in the temperature range 170°C–230°C. Depending on the catalyst and reaction conditions, the main products of the reaction are cyclohexanone oxime, cyclohexylidenecyclohexylamine or cyclohexanone. About 70% selectivity of cyclohexanone oxime formation at about 20% conversion of cyclohexylamine is obtained over tungsten catalysts. The activity of the tested catalysts usually passes through a maximum and, then, gradually decreases with time on stream. The deactivation of the catalyst is caused by the formation of tar products on the catalyst surface. The mechanism of oxidation involves formation of oxygen species on the catalyst surface which oxidizes cyclohexylamine.