A. N. Kalenchuk

Comparing the activities of catalysts in perhydro- m -terphenyl dehydrogenation

The activities of various catalysts based on Pt, Pd, Cr, and Ni in perhydro-m-terphenyl dehydrogenation have been compared in order to develop new catalytic composites based on organic compounds for hydrogen storage. Catalytic tests have been carried out at 300–320°C in a flow reactor with an inner diameter of 10 mm. The largest amount of hydrogen released as a result of perhydro-m-terphenyl dehydrogenation to m-terphenyl is observed with the (3% Pt)/Sibunit catalyst at 320°C. The maximum selectivity toward complete dehydrogenation is 95% in this case.

Effect of the structure of the ortho, meta, and para isomers of perhydroterphenyl on their reactivity in heterogeneous catalytic dehydrogenation

The kinetics of the dehydrogenation of the individual ortho, meta, and para isomers of perhydroterphenyl and their mixtures over a (3 wt % Pt)/C catalyst has been investigated in a flow reactor at 280–340°C. The rate of the isomerization of the stereoisomers of the initial substrate (perhydroterphenyl) and terphenyl dehydrogenation products has an effect on the hydrogen release kinetics. The highest reactivity in isomerization is shown by the ortho isomer. The largest amount of hydrogen (7.0 wt %) is released in the dehy-drogenation of perhydro-meta-terphenyl and perhydro-para-terphenyl, whose conversion at 320°C is 96%.

Kinetics of decalin dehydrogenation on Pt/C catalyst

Catalytic dehydrogenation of decalin (decahydronaphtalene), a promising material for hydrogen storage, has been investigated. The amount of hydrogen produced on a Pt (3 wt.%)/C catalyst has been studied as a function of pressure, temperature, and the substrate feed rate in a flow-type reactor. The maximum volume of the released hydrogen is achieved at atmospheric pressure, a temperature of 320 °C and a substrate LHSV of 1 h–1. The dehydrogenation occurs mainly by conversion of cis(97%) and partial conversion of trans-decalin (66%) with a selectivity of 97% to naphthalene. The amount of the released hydrogen corresponds to the decalin hydrogen capacity (5.5 wt. %). The obtained results are consistent with the calculated thermodynamic characteristics of the studied reaction.

Hydrogenation of biphenyl and isomeric terphenyls over a Pt-containing catalyst

Catalytic hydrogenation of benzene, biphenyl, and ortho-, metha-, and para-isomers of terphenyl over a 3 wt.% Pt/C at 180 °C and 70 atm was studied. The directions of hydrogenation of each substrate were revealed. Relationships between structures of the substrate and hydrogen consumption rates were found. It was shown that hydrogenation rate decreases on going from benzene to terphenyl and with increasing degree of the substrate hydrogenation. Hydrogenation rate of terphenyl isomers decreases in the following order: p-terphenyl > > m-terphenyl > o-terphenyl.

Kinetic and thermodynamic parameters of hydrogen release during the heterogeneous catalytic dehydrogenation of cis- and trans-isomers of perhydro-m-terphenyl

Comparative studies on the temperature dependence of the dehydrogenation of cis- and trans-isomers of perhydro-m-terphenyl are performed in a flow catalytic reactor. Rate constants and equilibrium constants of all elementary acts of this reaction are calculated on basis of experimental data using the KINET 0.8 program for the mathematical modeling of the kinetics of complex reactions. The resulting data indicate that perhydro-m-terphenyl cis- and trans-isomers structural differences have no appreciable effect on dehydrogenation.

Hydrogenation of Anthracene and Dehydrogenation of Perhydroanthracene on Pt/C Catalysts

The hydrogenation of anthracene on a heterogeneous catalyst containing 3 wt % Pt/C (Aldrich) at 215, 245, and 280°C and the pressures of 40 and 90 atm is studied. The hydrogenation of anthracene to a completely hydrogenated product is considered in detail. The final product (perhydroanthracene) consists of five conformational isomers with total selectivity of more than 99%. The ratio of perhydroanthracene isomers in the end product is shown to be determined by the conditions (P, T) of hydrogenation. The rate of hydrogenation is found to slow upon an increase in the degree of benzene ring saturation. A mixture of perhydroanthracene isomers is dehydrogenated in an autoclave at 260−325°C on 3 wt % Pt/C catalyst (Aldrich) and in a flow reactor at 300–360°C on 3 wt% Pt/Sibunit catalyst. The reactivity of perhydroanthracene isomers in dehydrogenation is shown to differ.

Reversible hydrogenation—dehydrogenation reactions of meta -terphenyl on catalysts with various supports

For developing new composite systems (substrate—catalyst) for hydrogen storage, the activities of Pt and Pd catalysts on various supports were compared in reversible meta-terphenyl hydrogenation and perhydro-meta-terphenyl dehydrogenation. The microstructure of the catalysts was studied. Carbon-supported catalysts are more efficient in both reversible reactions than alumina-supported systems.

Deactivation of a mixed oxide catalyst of Mo–V–Te–Nb–O composition in the reaction of oxidative ethane dehydrogenation

The operational stability of a mixed oxide catalyst of Mo–V–Te–Nb–O composition in the oxidative dehydrogenation of ethane (ratio of C2H6: O2 = 3: 1) is studied in a flow reactor at temperatures of 340–400°C, a pressure of 1 atm, and a WHSV of the feed mixture of 800 h−1. It is found that the selectivity toward ethylene is 98% at 340°C, but the conversion of ethane at this temperature is only 6%; when the temperature is raised to 400°C, the conversion of ethane is increased to 37%, while the selectivity toward ethylene is reduced to 85%. Using physical and chemical means (XPS, SEM), it is found that the lack of oxidant in the reaction mixture leads to irreversible changes in the catalyst, i.e., reduced selectivity and activity. Raising the reaction temperature to 400°C allows the reduction of tellurium by ethane, from the +6 oxidation state to the zerovalent state, with its subsequent sublimation and the destruction of the catalytically active and selective phase; in its characteristics, the catalyst becomes similar to the Mo–V–Nb–O system containing no tellurium.

Catalytic oxidative coupling of dimethyl ether under supercritical conditions

Catalytic oxidative coupling of dimethyl ether (DME) is studied for the first time under supercritical conditions. The oxidation of DME with molecular oxygen of air in the presence of the CaO-SnO2 catalyst is carried out in a substrate (DME) medium and in its mixtures with CO2 under the supercritical conditions (100 atm, 250–300°C). At 255°C, the maximum conversion of DME (≈40% at the ratio of the yields of monoglim and diglim about 2: 1) is achieved at a 20-fold (by volume) dilution of DME with supercritical CO2.

Hydrogenation of naphthalene and anthracene on Pt/C catalysts

Hydrogenation of naphthalene and anthracene deposited on Sibunit and active carbon was studied. The reactions were carried out at a temperature of 280 °C and a pressure of 90 atm. The directions for the complete hydrogenation of the investigated substrates were studied. Correlations between the structures of naphthalene and anthracene and their activity in hydrogen absorption are presented. The hydrogenation rates decrease as the substrate is saturated with hydrogen.