H. Frank Leach

Comparison of the shape selective properties of ferrierite, ZSM-5 and ZSM-11

Characterization of the pore structures of ferrierite, ZSM—5 and ZSM—11 was performed by measuring the rates and extents of adsorption of a series of molecules of different kinetic diameters. The results were consistent with the reported pore dimensions of the three zeolites. Comparison of activities and selectivities in methanol conversion revealed a direct correlation between the nature of the intracrystalline pore structure and the aromatic product distribution. In addition, a marked enhancement in p-xylene selectivity was observed for mixed ferrierite/ZSM—5 catalysts. Results obtained during but-1-ene isomerization were consistent with an acid-catalysed mechanism involving the secondary butyl carbenium ion as reaction intermediate. A significant feature of but-1-ene isomerization over ferrierite was the marked preferential formation of cis-but-2-ene as reaction product. This was attributed to restricted rotation of the secondary butyl carbenium ion within the constrained environment of the ferrierite pore structure (that is, as a consequence of transition-state selectivity).

The exchange of methane, ethane, and propane with deuterium on silica-supported nickel catalyst

Abstract The rates and product patterns for the exchange of methane, ethane, and propane on nickel/silica catalysts are reported. The principal products were CH 3 D and CH 4 for methane, C 2 H 4 D 2 , C 2 H 2 D 4 , and C 2 D 6 for ethane, and C 3 H 7 D and C 3 H 6 D 2 for propane. The results are interpreted in terms of competition between deuterium and hydrocarbon molecules for adsorption on different specific surface sites.

Some sorptive and catalytic properties of zeolite Nu—10

Abstract Characterization of the pore structure of zeolite Nu—10 was performed by measuring the rates and extents of adsorption of a range of molecules of different kinetic diameter. The results were indicative of a pore structure similar to that found in ZSM—5, comprising apertures of diameter 0.6 nm. Results obtained during methanol conversion, however, revealed a cut-off in the hydrocarbon product distribution at C6, which is indicative of a more constrained environment within the pore structure of Nu—10 relative to that in ZSM—5. This suggests that Nu—10 is devoid of large channel intersections of the type found in ZSM—5 and other pentasil zeolites. The preferential formation of trans-but-2-ene observed during but-1-ene isomerization over Nu—10 is consistent with a pore structure of this type; the slower diffusion of the larger cis-but-2-ene isomer within the intracrystalline pore structure giving rise to secondary cis-trans isomerization and formation of the thermodynamically favoured trans-but-2-ene.

Reactions of alkenes and the equilibration of hydrogen and deuterium on zirconia

The hydrogenation of various alkenes, the equilibration of H2/D2 and the isomerisation of some C6-alkenes have been studied over a range of temperatures on zirconia catalysts. Products from the reaction of some of the alkenes with deuterium were examined by 2D n.m.r. spectroscopy. The rate of hydrogenation varied only to a small extent with the nature of the alkene, apart from some steric hindrance with some of the C6-compounds, and the supply of hydrogen to the surface appeared to be rate-determining. Reactions of alkenes with deuterium below 400 K gave D2-alkanes. As the temperature was raised, exchange of alkene was observed to an increasing extent, and the location of the deuterium atoms in the products provided evidence of possible mechanisms.

Synthesis, properties, and catalytic behavior of zeolite EU-12

Abstract The synthesis and characterization of EU-12, a novel thermally stable high-silica zeolite, are described. Sorption measurements indicate that access to the zeolitic void space is through windows with a free diameter of ∼ 0.40 nm. Ion exchange gives a hydrogen form that shows preferential formation of ethene in methanol conversion and the selective formation of cis -but-2-ene in but-1-ene isomerization.

Degradation of AlPO4-5 by aqueous salt solutions

Calcined template-free AlPO4-5 is attacked by liquid water and aqueous salt solutions at 25°C, whereas the “as-made” material is resistant to degradation. The extent to which the framework is attacked increases with the salt concentration and depends on the nature of the anion (OH− > I− > S2O32− > Br− > Cl−). Phosphate is released to the solution phase and the pH decreases from ∼ 5.5 to ∼ 3.0. AlPO4-11 and AlPO4-25 are also attacked by salt solutions, but the effects are smaller than for AlPO4-5.

Determination of the active site and mechanism for alkene isomerization in CuII exchanged Y-type zeolite

Reactions of CD2CH—CH3, but-1-ene and 3,3-dimethylbut-1-ene have been studied over a Y-type zeolite containing ∼4 CuII per unit cell. Kinetic induction periods, associated with the generation of active sites by CuII reduction, were only observed for the deuterium redistribution reactions of CD2CH—CH3. Nevertheless, arguments are presented to show that such generation of active sites is central to alkene isomerization reactions over CuII exchanged X- and Y-type zeolites. The mechanism of alkene isomerization is shown to require carbonium ions, generated from protons produced following CuII reduction by the alkene.

Interactions of dienes and alkynes with rutile (titanium dioxide)

The catalytic properties of titanium dioxide (rutile) have been examined for a number of reactions involving dienes (propadiene and buta-1,3-diene) or alkynes (ethyne, propyne and but-2-yne) with hydrogen, deuterium or deuterium oxide.The isomerization of propadiene to propyne and the exchange of the methine hydrogen atom of the latter with deuterium oxide occur below 370 K.The main reaction with all the compounds, but particularly the alkynes, was a loss of hydrocarbon to the surface at 470 K or above to form a residue which was probably oligomeric. This process was accompanied by some formation of alkenes from buta-1,3-diene and to a much smaller extent from the alkynes; the reaction was not affected by the presence of gas phase hydrogen or deuterium and was essentially a self-hydrogenation of the unsaturated compounds. Water inhibited the formation of residue and the self-hydrogenation of buta-1,3-diene, and an exchange reaction occurred if deuterium oxide was used.The influence of various pretreatments on the catalytic properties of titanium oxide were examined and possible intermediates for some of the reactions are proposed.

Reactions of alkenes on lanthana

Abstract Reactions of ethene, propene, butenes, 2-methylpropene, cyclopentene, 2,3-dimethylbut-1-ene, and 3,3-dimethylbut-1-ene have been studied with hydrogen, and sometimes deuterium, on lanthana catalysts. Many alkene/lanthana systems show evidence of self-poisoning which is more marked with straight-chain hydrocarbons than with branched hydrocarbons and at higher temperatures; the catalysts are also highly sensitive to impurities. The temperature required to attain a fixed rate of hydrogenation (10 16 molecules s −1 m −2 ) varied from 220 K for ethene to over 373 K for the 2,3-dimethylbutenes. Fast hydrogenation without accompanying deuterium exchange was observed with alkenes which cannot form allylic species. The ability to form such species led to rapid isomerization of the butenes below 273 K and of 2-3-dimethylbut-1-ene at 373 K, and to exchange rates with deuterium which were comparable to (propene) or faster than (2-methylpropene) addition reactions at 380 K. Deuterium NMR spectroscopy was used for analysis of the products from the reactions with deuterium. Although the hydrogenation of 3,3-dimethylbut-1-ene occurred readily at 245 K, no isomerization was detected even at 510 K.

Isomerization Reactions of Substituted Cyclopropanes Over Zeolite Omega

Abstract The isomerization reactions of methylcyclopropane, 1,1-dimethylcyclopropane, and 1,2-dimethylcyclopropane have been studied in a static system over an omega zeolite pretreated at various temperatures. The maximum catalytic activity of the zeolite occurred at a pretreatment temperature which corresponded to the generation of maximum surface area, and was closely related to the conditions under which tetramethylammonium species encapsulated within the initial zeolite during synthesis were decomposed. The kinetics of the reactions of the substituted cyclopropanes were first order in the temperature range 230–330 K. Initial product distributions indicated kinetic rather than thermodynamic control, and have been rationalized in terms of a proton addition mechanism.