T. V. Vasina

Aromatization of ethane over Pt,Ga/HZSM-5 catalyst and the effect of intermetallic hydrogen acceptor on the reaction

The effect of the hydride-forming intermetallic compound Zr2Fe on the aromatization of ethane over Pt,Ga/HZSM-5 catalyst has been studied under different reaction conditions (temperature, GHSV, ethane dilution with Ar). In the presence of intermetallic hydrogen acceptor aromatics yield from ethane at 500°C was 6-fold higher and reached 61 wt.-% as a result of releasing hydrogen elimination, selectivity to aromatics being 78%. The fused-ring aromatics formation appeared to be more sensitive to hydrogen removal than BTX formation. The yield of BTX may be improved by ethane dilution with inert gas.

Isomerization of cyclic hydrocarbons mediated by an AlCl3-BASED ionic liquid as catalyst

Cyclohexane and methylcyclopentane isomerization were carried out under mild conditions using an ionic liquid consisting of n-butylpyridinium chloride and aluminum chloride as catalyst. The ionic liquid showed reasonably high catalytic activity in both reactions with a selectivity to corresponding products of 100%. In the case of cyclohexane isomerization, the thermodynamic equilibrium methylcyclopentane ⇌cyclohexane was almost achieved. For the reaction of cyclohexane isomerization, the kinetic study was performed, and the rate constants and the activation energy of the process were determined.

Cyclohexane ring opening on metal-oxide catalysts

Ring opening of cyclohexane on various metal-containing oxide catalysts is studied in detail. Rhodium supported on neutral alumina is shown to exhibit the highest selectivity toward n-hexane, whereas the formation of side products of cracking, isomerization and dehydrogenation (C 1 –C 4 hydrocarbons, isohexanes + methylcyclopentane, and benzene, respectively) is essentially suppressed.

Physicochemical characterization and catalytic properties of solid superacids based on sulfated zirconia modified with supported platinum

The acidic properties and electronic state of platinum in superacidic catalysts based on sulfated zirconia are studied by diffuse-reflectance IR spectroscopy. The spectroscopic data indicate a positive charging of platinum microparticles due to the interaction with strong Broensted acid sites, which presumably represent delocalized protons and are characterized by a broad absorption band at ~3100 - 2950 cm-1. For the ZrO2 sample, however, it is likely that a partial negative charge is induced on the metal particle due to the influence of the ZrO2 support which reveals basic properties. The sulfated systems were shown to exhibit high activity and selectivity in n-butane isomenzation. Plausible reaction pathways and intermediates are discussed.

Aromatization of ethane over modified pentasils

Abstract Aromatization of ethane over high silica zeolites modified by Zn, Ga or Pt was studied in the presence of intermetallic hydrogen acceptor Zr2Fe. Elimination of hydrogen formed during the reaction at 500–550°C by acceptor resulted in 4–6 fold higher aromatics yield, aromatization selectivity reaching 74–90%. In the similar conditions the effect of hydrogen absorption by Zr2Fe on ethane dehydrogenation appeared to be negligible over supported Ga2O3 or Cr2O3 and strongly negative in the case of Pt-containing catalysts. General considerations of the reaction mechanism are discussed.

Hydroisomerization of C6–C14 n-Alkanes over Hybrid Catalysts

Various hybrid catalysts prepared by mechanically mixing Pt(Pd) promoted oxides (Al2O3, SiO2) and an acidic component (RE-FAU, H-Beta zeolites and SO4/ZrO2 solid Superacid) were studied in C6–C14 n-alkane skeletal isomerization. The hybrid catalysts exhibited high activity and selectivity in paraffin isomerization. The enhancement in the activity of hybrid catalysts as compared to individual components was rationalized in terms of spillover of reactive species between metal promoted oxide systems and acidic sites.

Cyclohexane transformations over metal oxide catalysts. 1. Effect of the nature of metal and support on the catalytic activity in cyclohexane ring opening

The activities of monometallic Pt-, Ru-, and Rh-containing catalysts supported on Al2O3, Al2O3—F, SiO2, WO3/ZrO2, and La2Î3/ZrO2, in cyclohexane ring opening to form n-hexane were studied. The most active catalyst is Rh/Al2O3. Cyclohexane hydrogenolysis to n-hexane also occurs over the Pt/Al;>2O3 and Pt/La2Î3/ZrO2 catalysts. Ring opening over the Ru catalysts proceeds at significantly lower temperatures (210—230 °C) than over the Pt and Rh catalysts (350—400 °C), but the ruthenium systems are less selective for n-hexane formation than Rh/Al2O3 catalysts. The effects of acid-basic properties of the support and the reaction conditions on the activities of the catalytic systems in cyclohexane ring opening was studied.

The transformations of toluene on alumina and bifunctional catalysts

The activity of Pt, Rh, and Ni catalysts deposited on Al2O3 and tungsten-containing catalysts 20% H4SiW12O40/ZrO2 and 15% WOx/ZrO2 in the hydrogenation of toluene and toluene ring opening and isomerization in the presence of hydrogen was studied. Under experimental conditions (160–360°C, 2.2 MPa), the main reactions on Rh/Al2O3 were the hydrogenation of toluene into methylcyclohexane, hydrogenolysis into isoheptanes, and hydrocracking into alkanes C1–C6. On Pt, Rh, and Ni catalysts on carriers with strong acid properties, the isomerization of the six-membered into five-membered ring followed by hydrogenolysis (hydrocracking) of alkylcyclopentanes occurred. The yield of heptane isomers, however, did not exceed 13%. The activity of Pt and Rh catalysts on a high-acidity carrier (WOx/ZrO2) in hydrocracking was much higher than that of catalysts based on deposited heteropoly acid. The yields of hydrogenolysis (hydrocracking) products on Ni/WOx/ZrO2 were much lower than on Pt(Rh)/WOx/ZrO2. The highest yield of ring opening products (isoheptanes and n-heptane) was obtained with layered loading of two catalysts; it reached 58 wt % at 300°C and a 2.2 MPa pressure, which was 4.5 and 2 times higher than the yield obtained on Ni-Pt/WOx/ZrO2 and 2% Rh/Al2O3 catalysts. Hydrodemethylation was not the main direction of toluene transformations on any of the catalysts studied.

Cyclohexane transformations over metal oxide catalysts: 2. Selective cyclohexane ring opening to form n-hexane over mono- and bimetallic rhodium catalysts

The activity of monometallic Rh and Pt catalysts and bimetallic Pt—Rh catalysts on oxide supports in cyclohexane ring opening to form n-hexane was studied. The Rh-containing catalysts are highly active and selective in this reaction. Cyclohexane dehydrogenation predominates in the case of the Pt catalysts. The use of the bimetallic alumina-supported Pt—Rh catalysts allows one to minimize the contribution of cyclohexane cracking and to enhance the selectivity for n-hexane with the yield of the latter slightly depending on the metal ratio in the bimetallic system under the experimental conditions.

Suggestion on a new alternative mechanism of the sulfuric acid catalyzed isioparaffin-olefin alkylation

Abstract 13 C NMR study of the two-step isoparaffin-olefin alkylation indicated that alkyl carbenium ions are formed instead of protonation of olefins by protonation of alkylsulfates. In the case of sulfuric acid catalyzed alkylation of isoparaffins with propylene the low yield of propane indicates only a minor role in alkylation of a hydride transfer. Both those findings are in contradiction with the classical mechanism by Schmerling. Therefore, a new alternative mechanism of the two-step isoparaffin-olefin alkylation is proposed. It involves a direct alkylation of isoparaffins by alkylsulfates.