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Faraday Discuss ; 188: 451-466, 2016 07 04.
Artigo em Inglês | MEDLINE | ID: mdl-27095631


Porous manganese oxide (OMS-2) and platinum supported on OMS-2 catalysts have been shown to facilitate the hydrogenation of the nitro group in chloronitrobenzene to give chloroaniline with no dehalogenation. Complete conversion was obtained within 2 h at 25 °C and, although the rate of reaction increased with increasing temperature up to 100 °C, the selectivity to chloroaniline remained at 99.0%. Use of Pd/OMS-2 or Pt/Al2O3 resulted in significant dechlorination even at 25 °C and 2 bar hydrogen pressure giving a selectivity to chloroaniline of 34.5% and 77.8%, respectively, at complete conversion. This demonstrates the potential of using platinum group metal free catalysts for the selective hydrogenation of halogenated aromatics. Two pathways were observed for the analogous nitrobenzene hydrogenation depending on the catalyst used. The hydrogenation of nitrobenzene was found to follow a direct pathway to aniline and nitrosobenzene over Pd/OMS-2 in contrast to the OMS and Pt/OMS-2 catalysts which resulted in formation of nitrosobenzene, azoxybenzene and azobenzene/hydrazobenzene intermediates before complete conversion to aniline. These results indicate that for Pt/OMS-2 the hydrogenation proceeds predominantly over the support with the metal acting to dissociate hydrogen. In the case of Pd/OMS-2 both the hydrogenation and hydrogen adsorption occur on the metal sites.

ChemCatChem ; 8(3): 562-570, 2016 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-26925172


The mono(µ-oxo) dicopper cores present in the pores of Cu-ZSM-5 are active for the partial oxidation of methane to methanol. However, copper on the external surface reduces the ratio of active, selective sites to unselective sites. More efficient catalysts are obtained by controlling the copper deposition during synthesis. Herein, the external exchange sites of ZSM-5 samples were passivated by bis(trimethylsilyl) trifluoroacetamide (BSTFA) followed by calcination, promoting selective deposition of intraporous copper during aqueous copper ion exchange. At an optimum level of 1-2 wt % SiO2, IR studies showed a 64 % relative reduction in external copper species and temperature-programmed oxidation analysis showed an associated increase in the formation of methanol compared with unmodified Cu-ZSM-5 samples. It is, therefore, reported that the modified zeolites contained a significantly higher proportion of active, selective copper species than their unmodified counterparts with activity for partial methane oxidation to methanol.

Chem Commun (Camb) ; 46(34): 6279-81, 2010 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-20664876


Selective hydrogenation of carboxylic acids to alcohols and alkanes has been achieved under remarkably mild reaction temperatures and H(2) pressures (333 K, 0.5 MPa) using Pt/TiO(2) catalyst.

Álcoois/química , Álcoois/síntese química , Ácidos Carboxílicos/química , Platina/química , Titânio/química , Alcanos/síntese química , Alcanos/química , Catálise , Hidrogenação
Chem Commun (Camb) ; (7): 903-5, 2005 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-15700076


Chloroindate(III) ionic liquids are versatile reaction media for Friedel-Crafts acylation reactions; the system is catalytic and totally recyclable, using an aqueous workup, with no leaching of the indium into the product phase.

Hidrocarbonetos Aromáticos , Índio/química , Acilação , Catálise , Hidrocarbonetos Aromáticos/síntese química , Hidrocarbonetos Aromáticos/química , Estrutura Molecular , Fatores de Tempo
J Phys Chem B ; 109(40): 19018-25, 2005 Oct 13.
Artigo em Inglês | MEDLINE | ID: mdl-16853448


Raman spectra of the ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]), 1-hexyl-3-methylimidazolium chloride ([C6mim]Cl), and 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6mim][PF6]), and binary mixtures thereof, have been assigned using ab initio MP2 calculations. The previously reported anti and gauche forms of the [C4mim]+ cation have been observed, and this study reveals this to be a general feature of the long-chain 1-alkyl derivatives. Analysis of mixtures of [C6mim]Cl and [C6mim][PF6] has provided information on the nature of the hydrogen bonding between the imidazolium headgroup and the anions, and the invariance of the essentially 50:50 mixture of the predominant conformers informs on the nature of glass formation in these systems.

Chemistry ; 10(18): 4640-6, 2004 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-15378643


Heterogeneous catalytic oxidation of a series of thioethers (2-thiomethylpyrimidine, 2-thiomethyl-4,6-dimethyl-pyrimidine, 2-thiobenzylpyrimidine, 2-thiobenzyl-4,6-dimethylpyrimidine, thioanisole, and n-heptyl methyl sulfide) was performed in ionic liquids by using MCM-41 and UVM-type mesoporous catalysts containing Ti, or Ti and Ge. A range of triflate, tetrafluoroborate, trifluoroacetate, lactate and bis(trifluoromethanesulfonyl)imide-based ionic liquids were used. The oxidations were carried out by using anhydrous hydrogen peroxide or the urea-hydrogen peroxide adduct and showed that ionic liquids are very effective solvents, achieving greater reactivity and selectivity than reactions performed in dioxane. The effects of halide and acid impurities on the reactions were also investigated. Recycling experiments on catalysts were carried out in order to evaluate Ti leaching and its effect on activity and selectivity.

Germânio/química , Pirimidinas/química , Sulfetos/química , Titânio/química , Catálise , Estrutura Molecular , Oxirredução , Tamanho da Partícula , Porosidade , Dióxido de Silício/química , Solventes/química , Sulfetos/síntese química