Low temperature hydrogenation of 1- and 2-phenylethanols with noble metal catalysts in supercritical carbon dioxide (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.
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.
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.
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.
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 Surface Science, 2013
Ruthenium catalysts supported on activated carbons, original (AC) and treated with nitric acid (AC-Ox) were prepared by incipient wetness impregnation from either chloride (Cl) or nitroxyl nitrate (n) precursors. These catalysts were characterized by TG, XPS, TEM, TPD-MS and CO adsorption microcalorimetry and evaluated in the hydrogenolysis of glycerol in the liquid phase, at 453 K and 8 MPa. Studies by TEM show that ruthenium particles supported on AC-Ox are larger than on AC, without any effect of the nature of the metal precursor. However, adsorption of CO on the ex-chloride catalysts is inhibited in comparison with that of the ex-nitroxyl nitrate catalysts. Catalysts characterization by TG, TPD-MS and XPS reveals that the nitric acid treatment and the nitroxyl nitrate precursor generate oxygenated groups on the carbon surface, which provide acid properties to the catalysts, although they are partly destroyed during the reduction treatment applied to the catalysts. The sequence of the overall TOF, Ru(Cl)/AC < Ru(n)/AC < Ru(Cl)/AC-Ox ≈ Ru(n)/AC-Ox, reasonably parallels the population increase of surface acid groups. Participation of the COOH groups in the transformation of glycerol into 1,2-propanediol is verified by using the admixture Ru(Cl)/AC+AC-Ox as catalyst. In this case, since AC-Ox was not thermally treated and no loss of oxygenated groups occurred, TOF and selectivity toward 1,2-propanediol improve in comparison with those of the more active catalysts.
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.
2003
The selective oxidation of 1-and 2-propanol by molecular oxygen over supported platinum catalysts was investigated in ''supercritical'' carbon dioxide as an environmentally benign and safe reaction medium. The reaction occurs exclusively to acetone or propionic aldehyde and propionic acid in a single-phase region at 100-190 bar and at a mild temperature (40 C). Compared to conversions in aqueous solution, catalyst stability is significantly enhanced in ''supercritical'' carbon dioxide and depends on the oxygen concentration in the reaction medium. Thus, at least a fourfold higher substrate/catalyst ratio than with water as a solvent can be used. Platinum catalysts with nanoporous silica (MCM-41, silicalite-1) as a support are also active for the oxidation of 2-propanol in ''supercritical'' carbon dioxide.
Applied Catalysis A: General, 2013
The selective hydrogenation of cinnamaldehyde by a RhCl(TPPTS) 3 aqueous solution, ex situ synthesised from RhCl 3 • nH 2 O and TPPTS (tris(M-sulphonatophenyl)phosphine) with pH control by NaOH solution, was investigated under a biphasic (water/toluene) system in a batch reactor. The hydrogenation more usually occurred at C&C bonds, giving hydrocinnamaldehyde as the main product. Important parameters were varied carefully in order to maximise the selectivity toward hydrocinnamaldehyde for which the highest selectivity of 99.9% was achieved. Both the kinetic and mass transfer aspects were also evaluated and the results implied that the biphasic system was under mass transfer control. In addition, supported aqueous phase (SAP) catalysts of the RhCl(TPPTS) 3 solution supported on fine silica were prepared and tested for the selective hydrogenation of cinnamaldehyde under similar conditions for comparison and they gave a very high selectivity to hydrocinnamaldehyde which was an advantage, although their activity was lower than the biphasic catalysts. The mass transfer characteristic in SAP catalysis was also evaluated using a first-order film model.
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.