Tuning cis-decalin Selectivity in Naphthalene Hydrogenation Over Carbon-supported Rhodium Catalyst Under Supercritical Carbon dioxide (original) (raw)
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Chirality, 2000
A new "CO 2 -philic" chiral rhodium diphosphinite complex was synthesized and applied as catalyst precursor in the asymmetric hydrogenation of dimethyl itaconate in scCO 2 , scC 2 H 6 and various liquid organic solvents. Deuterium labeling studies and parahydrogen-induced polarization (PHIP) NMR experiments were used to provide the first detailed mechanistic insight into the activation and transfer of the dihydrogen molecule during hydrogenation in scCO 2 . Chemical interactions between CO 2 and reactive intermediates of the catalytic pathway could be excluded as possible explanations for the experimentally verified difference in the catalytic behavior in scCO 2 and hexane.
Advanced Synthesis & Catalysis, 2008
1% Palladium-doped acidic resin (Amberlyst 15; styrene-divinylbenzene matrix with sulfonic acid groups) is shown to be a highly active catalyst for the continuous catalytic hydrogenation of C=C bonds in supercritical carbon dioxide (scCO 2 ) without affecting C=O bonds. This 1% Pd/Amberlyst-15 catalyst promotes the industrially important selective formation of 2-ethylhexanal from crotonaldehyde in a "one-pot" pathway involving hydrogenation and aldol condensation with a number of merits. The selectivity behavior of 1% Pd/Amberlyst-15 is striking-ly different compared to that of 1% Pd/C and 1% Pd/Al 2 O 3 due to its prominent bifunctional nature based on sulfonic acid groups adjacent to metallic Pd sites. Hybrid "A C H T U N G T R E N N U N G [Pd n -H] + " sites are suggested to act as both metal and acid sites promoting the bifunctional catalysis.
Applied Catalysis A: General, 2005
Catalytic hydrogenation of biphenyl to bicyclohexyl, an organic hydrogen storage medium, was examined over supported transition metal catalysts in supercritical carbon dioxide solvent. The yield of bicyclohexyl was almost 100% over the charcoal-supported rhodium (Rh/C) and ruthenium (Ru/C) catalysts at the temperature of 323 K, which was much lower than that required for biphenyl hydrogenation in organic solvents (573 K). The initial activity was higher over the Rh/C catalyst, while the initial selectivity to bicyclohexyl was higher over the Ru/C catalyst. The conversion of biphenyl increased with increase in hydrogen and carbon dioxide pressures, while the selectivity to bicyclohexyl was independent of hydrogen and carbon dioxide pressures over both catalysts.
Advantageous heterogeneously catalysed hydrogenation of carvone with supercritical carbon dioxide
Green Chemistry, 2011
The hydrogenation of carvone was investigated for the first time in high-density carbon dioxide. The hydrogenation over 0.5 wt% Pd, or Rh, or Ru supported on alumina was found to be generally faster in a single supercritical (sc) phase (fluid reagents) than in a biphasic system (liquid + fluid reactants). The reaction with Pd produced fully hydrogenated products (isomers of carvomenthone) and carvacrol. The Rh catalyst was more selective and favoured carvomenthone isomers with higher selectivity and carvotanacetone as a secondary product. Additionally, the rhodium catalysed reaction exhibited high > 84% selectivity of carvotanacetone with the conversion of > 25% after only 2 min of reaction. The less active Ru catalyst gave significantly lower conversion and the product variety was greater as carvomenthone isomers, carvotanacetone and carvacrol were formed. The conversion and selectivity to carvomenthone within 2 h of the reaction starting followed the order: Pd > Rh > Ru and Rh > Pd > Ru, respectively. High conversion, and diverse and high selectivity accompanied by significant reduction in reaction time depending on the catalyst were achieved in supercritical CO 2 compared with hydrogenation occurring in conventional organic solvents.
Industrial & Engineering Chemistry Research, 2003
The kinetic studies on the hydrogenation of 1-octene and cyclohexene using a fluoroacrylate copolymer grafted rhodium catalyst in supercritical carbon dioxide (scCO 2 ) are reported. The reactions were investigated at temperatures between 50 and 120°C, and pressures ranging from 172 to 241 bar. The catalyst also deactivated at these reaction conditions. For the case of 1-octene, isomerization to (E)2-octene and (Z)2-octene also occurred as side reactions. To represent the experimental data, a kinetic model was developed on the basis of reported studies about hydrogenation and isomerization of olefins in conventional solvents. It was proposed that two hydride catalytic species are formed during the kinetic cycle. Monohydride species promoted the isomerization, and dihydride species catalyzed the hydrogenation. Deactivation of the catalyst was attributed to the formation of an unsaturated olefin complex. Statistical methods were applied to discriminate among rival models. It was found that the rate-determining steps for hydrogenation and isomerization were the formation of the alkylrhodium hydride complex and the coordination of the olefin in the monohydride catalytic species, respectively.
Advanced Synthesis & Catalysis, 2006
Continuous flow supercritical carbon dioxide (scCO 2 ) has previously been shown (P. Stephenson, P. Licence, S. K. Ross, M. Poliakoff, Green Chem. 2004, 6, 521) to be a viable medium for conducting continuous asymmetric hydrogenation when it is combined with an appropriate enantioselective catalyst. Here we examine the use of a composite catalyst immobilisation system modified with several different types of asymmetric bisphosphine ligands in continuous flow scCO 2 . In particular, proprietary ligands from Solvias AG were found to be the most successful, with Josiphos 001 improving the enantio-meric excess (ee) to> 80 % in the asymmetric hydrogenation of dimethyl itaconate (DMIT); this ee is higher than that reported for the batch hydrogenation of DMIT using a homogeneous catalyst fully dissolved in scCO 2 (S. Lange, A. Brinkmann, P. Trautner, K. Woelk, J. Bargon, W. Leitner, Chirality 2000, 12, 450).
Comparative study of the hydrogenation of tetralin on supported Ni, Pt, and Pd catalysts
Catalysis Today, 2007
The hydrogenation of tetralin in the vapor phase has been investigated over Ni, Pt, and Pd catalysts to determine the evolution of the trans-and cisdecalin products as a function of conversion over the different catalysts. The concentration of each isomer in the product may be important in subsequent ring opening steps if cetane number improvement is desired. The cis-decalin isomer is preferred to open the naphthenic ring in a selective way instead of multiple cracking. However, thermodynamically, this isomer is the least favored; so, kinetic control is the only solution. By selecting the proper catalyst and operating conditions, one could keep the trans/cis-decalin ratio low. In this study, we have prepared a series of supported metal catalysts and tested them in a flow reactor at 3540 kPa and 548 K. Kinetic parameters for the hydrogenation of tetralin and the cis-to-trans-decalin isomerization over the various catalysts investigated were obtained by fitting the data with a generalized Langmuir-Hinshelwood model.
Nanosized Pd/Pt and Pd/Rh Catalysts for Naphthalene Hydrogenation and Hydrogenolysis/Ring-opening
Catalysis Letters, 2006
Pd/Rh and Pd/Pt catalysts supported on two different mesoporous materials – a Zr-doped MCM-41-type silica [Si/Zr = 5 w/w (SiZr)] and a commercial silica-alumina [Si/Al = 40:60 w/w (SiAl)] – were prepared by incipient wetness impregnation using nanosized suspensions of alloy particles prepared by polyol-mediated synthesis in diethylene glycol (DEG). The catalytic behaviour of these catalysts was investigated in the hydrogenation and hydrogenolysis/ring-opening of naphthalene at 6.0 MPa, by checking the role of both the main reaction conditions (temperature, contact time and H2/naphthalene molar ratio) and increasing amounts of dibenzothiophene (DBT). The catalysts supported on SiAl showed higher activity than catalysts supported on SiZr, thus suggesting that activity is favoured by higher acidity of the support and/or higher interaction of the nanosized metal particles with the support. While using the SiZr support, weaker metal-support interactions took place by forming catalysts with bigger metal and/or metal oxide particles. Besides, the catalyst with lowest noble-metal content (0.3 wt.%) (SiAl-0.3Pd/Pt-5) had the greatest acidity and metal surface and, consequently, the highest activity. Furthermore, it exhibited a good thiotolerance in presence of increasing amounts of DBT in the feed, thus maintaining a high catalytic activity in the hydrogenation of naphthalene, although with decreased yield in trans- and cis-decalin (decahydronaphthalene or DeHN) and high-molecular-weight compounds (H.M.W.), with a corresponding increased yield in the partially hydrogenated tetralin (tetrahydronaphthalene or TeHN).
Catalysis Communications, 2009
Hydrogenation of 4-alkylphenols was studied over a carbon-supported rhodium catalyst in supercritical carbon dioxide (scCO 2) solvent, and the results were compared with those in 2-propanol. Higher selectivities to cis-4-alkylcyclohexanols were obtained in scCO 2 than in 2-propanol for the hydrogenation of all 4alkylphenols tested. In addition, the formation of alkylcyclohexane (dehydroxylated product) was suppressed in scCO 2. Stereoselectivities to cis forms were further improved in the presence of hydrochloric acid.