摘要:

AbstractIn this paper, recent results on the de‐oxygenation of some organic molecules nitrobenzene, aliphatic carboxylic acids and benzoic acid are reviewed. The activity pattern of metal oxides in these reactions has been established, and several factors controlling the selectivity have been identified. Selectivity in the de‐oxygenation (and related) reaction is related to the universally operatingMars ‐ Van Krevelenmech

ISSN:0165-0513    

DOI:10.1002/recl.19961151102

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractIn this article, we review the recent progress that has been made in the field of Lewis‐acid catalysis of carbon carbon‐bond‐forming reactions in aqueous solution. Since water hampers the hard hard interactions between the catalyst and the reactant, it often complicates catalysis. However, once coordination has taken place, water can have beneficial effects on rates and selectivities of Lewis acid catalysed Diels Alder reactions, aldol reactions, allylation reactions, Barbier and Mannich type reactions as well as Michael addi

ISSN:0165-0513    

DOI:10.1002/recl.19961151103

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractVanadyl‐ and nickel‐tetraphenylporphyrins (VO‐TPP and Ni‐TPP) have often been used as model compounds for the metallo‐porphyrin (‐like) fraction in heavy oil residua. The goal of the present work was to validate and to extend the present‐known reaction mechanism for the hydrodemetallization (HDM) of metallo‐tetraphenylporphyrins (M‐TPP). Based on molecular‐modelling calculations and GC‐MS analysis, new reaction intermediates could be identified and an extended reaction mechanism for the hydrodemetallization of metallo‐TPP proposed. The mechanism proceeds via three hydrogenation steps on β‐pyrrole positions of the porphyrinic structure to ameso‐bridge‐hydrogenated structure. After an acid attack, ring opening, and a possible elimination of a tolyl group, the final product before metal removal is an open‐chain molecule. Metal removal and further conversion leads to monopyrrole‐containing molecules and metal

ISSN:0165-0513    

DOI:10.1002/recl.19961151104

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractExploratory research to develop Rh‐free, “Pt‐only”, automotive catalysts is described. Metal oxides were added as a promoter or co‐catalyst to Pt/SiP2and the effect of the additive on NO reduction by CO has been studied. In addition, the reaction was studied over the unsupported metal oxides (MO) and Pt/MO catalysts. From the series of metal oxides tested, it is concluded that Co, Fe, Mn, Ti and V oxides show promising results as additives to Pt for the catalysis of NO reduct

ISSN:0165-0513    

DOI:10.1002/recl.19961151105

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe irreversible adsorbates formed after exposure of platinum to an NO‐containing solution were studied with Differential Electrochemical Mass Spectrometry (DEMS), Fourier‐Transform Infrared Spectroscopy (FTIRS) and cyclic voltammetry. DEMS and FTIRS show that only a very small amount of N2O is formed in the reduction of the adsorbate, indicating that mainly non‐volatile products are formed. FTIRS shows, in addition, vibrations of NO at wavenumbers characteristic of adsorbed NO on Pt(100) and Pt(110) sites. These two different adsorption sites are characterized by separate reduction peaks in the cyclic voltammogram. Further, it was established with FTIRS that the adsorbate is transformed to N2O and NH+4in the reduction, and to NO−3in the oxidation. Analysis of the charges involved in the reduction and oxidation of the irreversible adsorbates demonstrates that coadsorbates are present next to NO. The coadsorbates consist of adsorbed nitrogen atoms, formed by the dissociation of NO. This view is supported by previously reported studies in Ultra High Vacuum (UHV). A new mechanism for the reduction of NO to N2O in the liquid phase is proposed on the basis of NO disso

ISSN:0165-0513    

DOI:10.1002/recl.19961151106

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe kinetics of surface reactions of ethylene adsorbed on the (111) surface of a rhodium single crystal has been investigated by means of temperature‐programmed desorption and static secondary‐ion mass spectrometry (SSIMS). These reactions include the decomposition of ethylene to ethylidyne (CCH3), and the exchange of H for D‐atoms in the latter, the oxidation of adsorbed ethylene and its reaction with coadsorbed NO. The formation of relatively large amounts of HCN indicates that C‐N coupling on rhodium is possible under mild c

ISSN:0165-0513    

DOI:10.1002/recl.19961151107

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe phosphoramidites2–9have been applied as modifying ligands in rhodium‐catalysed hydroformylation of oct‐1‐ene and styrene. Monodentate phosphoramidites2–5gave rise to catalysts with average rates of 1000 mol [mol Rh]−1h−1and maximum selectivities of 65% to the linear product nonanal for the hydroformylation of oct‐1‐ene (P20 bar CO/H2,T80°C, [oct‐1‐ene] ≈︁ 1 M). Styrene was hydroformylated (T40°C,P20 bar CO/H2) at rates up to 150 mol [mol Rh]−1h−1and a selectivity for the branched 2‐phenylpropanal of 93%. Using diphosphoramidite modified catalysts a maximum rate of 1200 mol.[mol Rh]−1.h−1for oct‐1‐ene was observed for9, with 91% regioselectivity for the linear product. At 40°C styrene was hydroformylated at rates up to 25 mol [mol Rh]−1h−1and with selectivities for the branched aldehyde of 89%. Characterization of the rhodium complexes showed that formation of rhodium hydride complexes is slow and incomplete under the conditions applied for the monophosphoramidites. The diphosphoramidite ligands all form bidentate hydrido‐rhodium complexes. The diphosphoramidite ligands6–9coordinate bis‐equatorially in the trigonal bipyramidal rhodium compl

ISSN:0165-0513    

DOI:10.1002/recl.19961151108

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractLipoxygenase‐1 extracted from crude soybean‐flour was incubated with hydrolysed safflower oil as a substrate in a 7‐1 fermentor. Optimized reaction conditions included pH 10.0, 5°C and air saturation. Under these conditions production on a 40‐g/l scale can easily be carried out yielding up to 80% 13‐hydroperoxy‐9(Z), 11 (E)‐octadecadienoic acid with a stereo‐configuration of ess

ISSN:0165-0513    

DOI:10.1002/recl.19961151109

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe influence of process parameters such as temperature (400‐560K), H2/CCl2F2ratio (2.2‐20), and Weight Hourly Space Velocity (WHSV) (0.3‐1.0 g/(g · h)) on the hydrogenolysis of CCl2F2into CH2F2over palladium on activated carbon has been investigated. The reactivity of CHCIF2and CH2F2and the influence of HCl were also examined. In the reaction of CCl2F2, the main product is CH2F2. Significant amounts of CHCIF2and CH4are also found. The catalyst shows a remarkably high selectivity to CH2F2, in the range of 70‐90 mol%, at all conversion levels in a broad range of process conditions. A mechanism is proposed in which the reaction proceeds mainly via parallel reaction pathways. One route results in CH2F2and CHCIF2, while the other route yields CH4. The selectivity to CH2F2and CHCIF2is determined by the amount of adsorbed chlorine on the catalytic surface and a constant selectivity for CH4was found. High selectivity for CH2F2can be achieved at high H2/CCl2F2ratios and low HCl concentration. The postulated mechanism is supported by thermodyna

ISSN:0165-0513    

DOI:10.1002/recl.19961151110

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractPyridine bases were formed by the reaction of ethanol and ammonia over zeolite Nu‐10 in the presence of oxygen, which was shown to play an essential role. The use of different proton‐introduction procedures resulted in different activities and selectivities of the catalyst. H‐Nu‐10 and H‐ZSM‐5 showed substantially higher pyridine selectivity than H‐mordenite. In order to clarify the reaction mechanism of the title reaction, several other small amines and oxygenates were tested in the presence/absence of oxygen with respect to their selectivity towards pyridines. Zeolitic acid sites were shown to catalyse the dehydrogenation of ethanol, together with condensation, cyclization and aromatization, while structural defects probably produced oxidation products such as acetaldehyde and formaldehyde which are thought to play an important role in the reaction. The use of methylamine instead of ammonia greatly enhanced the pyridin

ISSN:0165-0513    

DOI:10.1002/recl.19961151111

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY