András Fási

Sonication assisted gold deposition on multiwall carbon nanotubes

Gold was successfully deposited on multiwall carbon nanotubes (MWNTs). It was achieved by applying a gold colloid stabilised by [tetrakis(hydroxymethyl)phosphonium chloride] (THPC) surfactant and ultrasonic irradiation during preparation. By controlling the quantity of gold and optimising sonication time up to 50 wt% gold could be deposited on MWNTs.

The selectivity and activity determining roles of carbonaceous species and metal–metal oxide interface in metal-catalyzed hydrogenation and isomerization reactions

Abstract The activity and/or selectivity determining roles of carbonaceous deposits of various kinds and metal–metal oxide interfaces are described in metal-catalyzed hydrogenation and isomerization reactions. The catalysts used were silica-supported Pt, Pd, Rh, Ni and Cu, while a wide range of probe molecules (cyclopropane, 1,1-dimethylcyclopropane, propylcyclobutane, methyloxirane, 2-methyl-2-butene, cyclohexene) were tested, in most cases, in the presence of H 2 or D 2 . The properties of catalytic surfaces were studied by infrared spectroscopy and kinetic methods in static or flow reactors. Six treatment or reaction types were applied for learning about surface transformations during or after the reaction. Carbonaceous deposits of various kinds were identified and their reaction influencing properties are analyzed. Metal–metal oxide interfaces are found to be crucial in the hydrogenative ring opening of methyloxirane and the roles of the metal and the metal oxide are elucidated as well.

The mechanism of hydrogenolysis and isomerization of oxacycloalkanes on metals XV. Transformation of ethyl- and vinyloxirane on Cu-SiO2

Abstract The isomerization and hydrogenolysis of vinyloxirane and, for comparison, those of ethyloxirane were studied on a Cu–SiO2 catalyst at 373 K in a recirculation reactor, at various hydrogen pressures and in the presence of deuterium. It was established that in the case of ethyloxirane, the dominating reactions are deoxygenation associated with the formation of 1-butene and isomerization resulting in the formation of butanal. In the case of vinyloxirane, the enlargement of the oxirane ring to a five-membered ring also takes place in addition to deoxygenation and isomerization. Olefins are formed on Cu(0) while isomerization occurs on copper–copper oxide interfaces. The experimental results allow the identification of the probable reaction pathways leading to the formation of the individual products.

Ring-Opening Reactions of Propylene Oxide (Methyloxirane) over Au/MgO and Unsupported Au Catalysts

The ring-opening reactions of propylene oxide (methyloxirane) were studied over an Au/MgO catalyst and Au powder at various temperatures in a pulse microreactor. The supported catalyst was significantly more active, and its activity was dramatically influenced by the method of pretreatment. When it was finished with hydrogen, conversion values were always above 70%, but often it was in the 90%+ range. The major reaction pathways were deoxygenation and isomerization. The comparison in the behavior of Au/MgO and Au powder pointed to the crucial importance of the support–metal interface in oxygen traffic and as a landing place for hydrogen-rich residues being the hydrogen source for water and alcohol formation (hydrogenation).

Cyclodimerisation and cyclotrimerisation during the ring-opening reactions of ethylene sulfide (thiirane) over acidic molecular sieves and alumina

The transformations of ethylene sulfide were studied at three reaction temperatures (423, 473 and 523 K) on different acidic molecular sieves (HZSM-5, HY and AlMCM-41) and alumina in a pulse system. The main reaction pathways were found to be desulfurisation, cyclo-oligomerisation, the latter being more important. In this reaction channel mainly direct dimer (six-membered ring: 1,4-dithiane) and trimer (1,4,7-trithiacyclononane) formation occurred. The former product was always predominant, however, 1,4,7-trithiacyclononane was also significant, especially on molecular sieves with larger pore openings and alumina. At elevated temperatures 2-methyl-1,3-dithiolane (a five-membered cyclic molecule) was also detected. This molecule was formed in the highest amount on HZSM-5 among the catalysts applied revealing that a more constrained environment is advantageous for this dimerisation type to occur.

23-P-15 - Ring opening reactions of methyloxirane over DZSM-5 and DAIMCM-41 molecular sieves-A mechanistic study

Publisher Summary This chapter presents the ring opening reactions of methyloxirane on DZSM-5 and DA1MCM-41 aluminosilicates in a pulse microreactor at 363 K. Deuterium distribution in the products is monitored. For deuterium, exchange to occur during ring opening at least one BrOnsted site is necessary. For the formation of deuterium-exchanged dioxolane derivatives two neighbouring BrOnsted–Lewis site pairs while for the formation of deuterium-exchanged dioxane derivatives the interplay of a BrOnsted–Lewis acid pair and a Lewis–Lewis acid pair seem to be the most advantageous.

Ring-opening reactions of ethyl- and vinyloxirane on HZSM-5 and CuZSM-5 catalysts

Transformations of ethyloxirane, vinyloxirane and their mixture were studied over HZSM-5 and CuZSM-5 zeolites in the presence of hydrogen at 363 K. Ethyloxirane underwent single ring-opening and deoxygenation, while ring expansion was the main transformation pathway for vinyloxirane. Reactions of the mixture revealed that the active sites for adsorbed oxygen mediated ring transformations can be separated on HZSM-5 from those, where the adsorption of the vinyl group and the ring oxygen is a requirement. This cannot be done on CuZSM-5.

The ring opening and oligomerisation reactions of an epoxide and an episulfide on aluminosilicates in the liquid phase

The ring opening reactions of propylene oxide (methyloxirane) or ethylene sulfide )thiirane) were studied in the liquid phase over HZSM-5, HY-FAU or AlMCM-41 at 363 K or 423 K and under 1 or 20 bar pressure in a batch reactor. The proportion of these routes were identified: (i) single C−O scission providing non-cyclic products, (ii) double C−O cleavage leading to the loss of the heteroatom, (iii) oligomerisation resulting in cyclic dimers and the trimer of thiirane and a non-cyclic dimer of methyloxirane. The reaction pathway depended on the conditions and the solid acids used. Findings are compared to those in the gas phase over the same solid acids. Transformation mechanisms are also suggested.

Effects of Substituents on the Ring-Opening Pathways of Oxiranes on ZSM-5 Zeolites

The ring-opening reactions of methyloxirane and ethyloxirane on ZSM-5 catalysts are dramatically different in spite of otherwise identical reaction conditions. Even though both reactants undergo single ring opening providing isomers of the starting compound, the major transformation route of methyloxirane is dimerization resulting in dioxolane and dioxane derivatives of various kinds. This reaction pathway, however, is completely lacking in the case of ethyloxirane. Molecular modeling revealed that possible dimers of ethyloxirane are too bulky to be formed and diffuse through the channel system of the ZSM-5 structure.

Transformation pathways of 2,2-dimethyloxirane on aluminosilicates: the effects of catalyst structure and reaction conditions

Abstract The ring transformation reactions of 2,2-dimethyloxirane were studied over various aluminosilicates (HZSM-5, CuZSM-5, HY, A1MCM-41 or NaN 3 -loaded A1MCM-41) in a pulse reactor at 423 K. The main reactions identified were isomerisation and cyclic dimerisation. The product formation selectivities could be tuned by varying the pore size of the molecular sieves and/or altering the reaction parameters. Large pore size and mild conditions favoured isomerisation, while an optimally constrained environment and overloading the catalyst with the epoxide (increased pulse size) was advantageous for cyclic dimerisation.