Biphenyl hydrogenation over supported transition metal catalysts under supercritical carbon dioxide solvent (original) (raw)
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Phenol hydrogenation over supported metal catalysts under supercritical carbon dioxide
Studies in Surface Science and Catalysis, 2004
Phenol hydrogenation was examined with several metal-loaded catalysts under supercritical carbon dioxide. A charcoal-supported rhodium catalyst was highly active for the ring hydrogenation. The selectivity to cyclohexanone and cyclohexanol was controlled by changing carbon dioxide and hydrogen pressures.
The Journal of Supercritical Fluids, 2006
Catalytic ring hydrogenation of 1-and 2-phenylethanols was studied over several noble metal catalysts supported on charcoal or ␥-alumina in supercritical carbon dioxide. The major products formed were corresponding cyclohexylethanols via aromatic ring hydrogenation of 1-and 2-phenylethanols while by products, ethylbenzene and cyclohexylethane were formed in minor quantities due to dehydroxylation reaction. A charcoal supported ruthenium catalyst gave the highest selectivity to (>80%) cyclohexylethanols among the other catalysts tested in this study at 323 K in supercritical carbon dioxide solvent.
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.
Journal of Catalysis, 2007
Hydrogenation of 2-, 3-, and 4-tert-butylphenols was studied over a charcoal-supported rhodium catalyst in supercritical carbon dioxide (scCO 2) solvent, and the results were compared with those in organic solvents. In the hydrogenation of 4-tert-butylphenol, a higher cis ratio for 4-tertbutylcyclohexanol (0.79) was obtained in scCO 2 (10 MPa) than in 2-propanol (0.70) and cyclohexane (0.64) under similar conditions of hydrogen pressure (2 MPa) and temperature (313 K). In the case of 2-tert-butylphenol, the cis ratio for 2-tert-butylcyclohexanol was as high as 0.95 in both scCO 2 and 2-propanol (hydrogen pressure, 2 MPa; reaction temperature, 313 K). In the case of hydrogenation of 3-tert-butylphenol, the cis ratio decreased with the progression of consecutive hydrogenation of 3-tert-butylcyclohexanone intermediate. In addition, the stereoselectivity to cis-tert-butylcyclohexanols in scCO 2 was improved in the presence of hydrochloric acid. It was found that the protons of hydrochloric acid accelerated the hydrogenation of the intermediates, tert-butylcyclohexanones, to the corresponding cis-tert-butylcyclohexanols. The hydrogenation mechanism of tert-butylphenols, particularly the enhanced selectivity to cis-tert-butylcyclohexanols in scCO 2 , is postulated based on the observed reaction profiles.
Hydrogenation of Carbon Dioxide on Supported Rh Catalysts
Catalysts
The constant increase in the CO2 concentration in the atmosphere requires us to look for opportunities to convert CO2 into more valuable compounds. In this review, the activity and selectivity of different supported metal catalysts were compared in the hydrogenation of carbon dioxide, and found that Rh is one of the best samples. The possibility of the CO2 dissociation on clean metal and on supported Rh was discussed separately. The hydrogenation of CO2 produces mainly CH4 and CO, but the selectivity of the reaction is affected by the support, in some cases the reduction of the support, the particle size of Rh, and the different additives. At higher pressure methanol, ethanol, and acetic acid could be also formed. The activity of the various supported Rh catalysts was compared and the results obtained for TiO2-, SiO2-, and Al2O3-supported catalysts were discussed in a separate chapter. The compounds formed on the surface of the catalysts during the reaction are shown in detail; most...
Catalysis Letters, 2006
Catalytic hydrogenation of naphthalene to decalin was studied over a carbon-supported rhodium catalyst in supercritical carbon dioxide solvent at 333 K, and the results were compared with those in an organic solvent. cis-, trans-Decalin and tetralin were formed from the beginning of the reaction in supercritical carbon dioxide. Higher concentration of hydrogen in carbon dioxide solvent and on the active site, and also the suppression of desorption of partially hydrogenated tetralin molecules from the active site would be responsible for higher selectivity to cis-decalin in supercritical carbon dioxide than that in an organic solvent.
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.
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.
ACS Omega
1-Phenylethanol (PhE) is widely employed in the pharmaceutical industry as an anti-inflammatory and analgesic drug, as well as in chewing gums and yogurts as a food additive. In this work, we have investigated the selective synthesis of 1-phenylethanol (PhE) by hydrogenation of acetophenone using supercritical CO 2 as a solvent. Supercritical carbon dioxide (scCO 2) replaces organic solvent because it is inexpensive, nontoxic, nonflammable, inert, and environmentally benign. Polyurea-based encapsulated mono-and bimetallic catalysts were synthesized and characterized using different characterization techniques. The effects of various reaction parameters, such as co-solvent, catalyst loading, hydrogen pressure, total scCO 2 pressure, and temperature, were studied to determine the reaction kinetics.