Search

The effectiveness of a multiphase medium including CO 2 and water was studied for the selective hydrogenation of various nitriles of 2-phenylethyl cyanide (PEC), cinnamonitrile, n -hexanenitrile (HN) and 4-cyanobiphenyl with a conventional Pd/Al 2 O 3 catalyst. Such a multiphase reaction medium was observed to have different impacts changing from one nitrile to another and the selective production of primary amine was achieved with PEC and HN but not with the other nitriles. Possible reasons for the substrate-dependent effects of CO 2 and water were discussed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Au–Pd/TiO2 were synthesized by the single step flame spray pyrolysis. [•] FSP resulted in more uniform and smaller Au–Pd particles compared to IMP and DP. [•] Rate of 1-heptyne hydrogenation depended on Pd dispersion and location. [•] Selectivity to 1-heptene was greatly modified by the presence of Au–Pd alloy. [ABSTRACT FROM AUTHOR]

Abstract: The present work has studied the influence of CO2 pressurization on the hydrogenation of nitrostyrene (NS) using Pt/TiO2. With CO2 pressurization up to 12MPa (CO2-dissolved expanded liquid (CXL) phase), the over-all reaction rate and the selectivity to aminostyrene (AS) increased. At higher CO2 pressures where all NS dissolved in scCO2 (scCO2-homogeneous phase), both of them decreased with increasing the CO2 pressure. The phase behavior was an important factor for the present reaction system. It was also found that the presence of pressurized CO2 gave higher selectivity to AS than in its absence at any conversion level. This was ascribed to retardation effects of dense phase CO2 on the hydrogenation of AS to ethylaniline. Competitive adsorption of nitro and vinyl groups was suggested to determine the product selectivity. FTIR measurements showed that the pressurized CO2 lowers the reactivity of the nitro group, and this effect is stronger in scCO2-homogeneous phase than in CXL phase, resulting in the lower AS selectivity in the former phase. Lower Pt loadings and higher catalyst reduction temperatures gave Pt/TiO2 catalysts more selective for the AS formation. FTIR measurements of adsorbed CO over the catalysts suggested that the presence of less-coordinated Pt atoms on edge, corner and kink sites was significant for the selective hydrogenation of NS to AS. [Copyright &y& Elsevier]

Abstract: A novel method for the synthesis of nanocrystalline zinc oxide without any additive was developed using zinc acetate and 1,4-butanediol through sonication. The structure and morphology of prepared nanocrystalline zinc oxide was investigated by various techniques like TEM, XRD, EDAX, UV–Vis spectroscopy. The solvent 1,4-butanediol played a dual role of fuel as well as capping agent eliminating addition of any extraneous species. The results showed that using ultrasound sonication is green, cost effective compared to conventional wet chemical method for ZnO nanoparticle synthesis. [Copyright &y& Elsevier]

Abstract: Hydrogenation of phenol to cyclohexanone and cyclohexanol in/under compressed CO2 was examined using commercial Rh/C and Rh/Al2O3 catalysts to investigate the effects of CO2 pressurization on the total conversion and the product selectivity. Although the total rate of phenol hydrogenation with Rh/C was lowered by the presence of CO2, the selectivity to cyclohexanone was improved at high conversion levels >70%. On the other hand, the activity of Rh/Al2O3 was completely lost in an early stage of reaction. The features of these multiphase catalytic hydrogenation reactions using compressed CO2 were studied in detail by phase behavior and solubility measurements, in situ high-pressure FTIR for molecular interactions of CO2 with reacting species and formation/adsorption of CO on the catalysts, and simulation of reaction kinetics using a simple model. The CO2 pressurization was shown to suppress the hydrogenation of cyclohexanone to cyclohexanol, improving the selectivity to cyclohexanone. The formation and adsorption of CO were observed for the two catalysts at high CO2 pressures in the presence of H2, which was one of important factors retarding the rate of hydrogenation in the presence of CO2. It was further indicated that the adsorption of CO on Rh/Al2O3 was strong and caused the complete loss of its activity. [Copyright &y& Elsevier]

Abstract: A catalyst system of ZnBr2/n-Bu4NI is reported for the first time as a highly efficient binary catalyst for the synthesis of styrene carbonate (SC) from styrene oxide and carbon dioxide under supercritical conditions. In a very short reaction time (30min) and even at a mild reaction temperature (80°C), 100% selectivity and nearly 100% yield of SC have been obtained; the TOF value obtained is 46 times larger than those so far reported under similar conditions. The effects of the ZnBr2/n-Bu4NI ratio, types of cation and anion, and other reaction conditions on the reaction were investigated. On the basis of the results, a reaction mechanism has been proposed. [Copyright &y& Elsevier]

Rhodium-catalyzed hydroformylation of 1,5-hexadiene and 1,7-octadiene to corresponding dialdehydes was investigated in compressed CO2 and in toluene using different fluorinated phosphine compounds as ligands. A rhodium complex using tris(3,5-bis(trifluoromethyl)phenyl)phosphine is highly effective in compressed CO2 for double hydroformylation of 1,5-hexadiene, whose TOF value is much larger than those reported so far. It has been shown that this ligand is effective also for the hydroformylation of 1,7-octadiene and scCO2 is a better solvent than a conventional organic solvent of toluene for the title reaction. [Copyright &y& Elsevier]

Using the form of supported liquid-phase catalysts, two or more homogeneous catalysts can simultaneously be used with retaining their own activities and taking the advantage of catalyst–product separation and catalyst recycling. [Copyright &y& Elsevier]