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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]

The photocatalytic H 2 production from a mixture of glycerol and water over NiO/TiO 2 catalysts was investigated. Effects of preparation and reaction conditions were examined, including TiO 2 materials, NiO loading, glycerol concentration, and pH value. The rate of H 2 production was observed to be maximized at a certain NiO loading and at a pH value close to the zero-point charge of TiO 2 . The influence of NiO loading may be explained by a decrease in the band gap energy and a decrease in the exposed area of TiO 2 , which were of importance in the ranges of small and larger NiO loading, respectively. At such a pH value, the amount of surface hydroxyl groups was likely to be maximized, which could promote the adsorption of glycerol molecules via hydrogen bonding. The change of the H 2 production rate with the glycerol concentration was explained assuming a Langmuir adsorption model. Both water and glycerol are involved in the photocatalytic H 2 production with NiO/TiO 2 catalysts. The reaction results with D 2 O instead of H 2 O indicate that glycerol may be a main H 2 source. In addition, it has been found that NiO is a good choice in preparing active TiO 2 based catalysts as compared with the other transition metal oxides of CoO and CuO. [ABSTRACT FROM AUTHOR]

The features of multiphase reaction media using water (bulk water, supported thin aqueous phase) and dense phase carbon dioxide are reviewed for selective hydrogenation of carbonyl, nitro, and cyano compounds. The interface of aqueous and organic phases is important in determining the rate of hydrogenation and the product selectivity. For supported aqueous phase catalysts, the interface between the thin aqueous film and a support material (for example, porous silica gel) has also an influential impact. The pressurization of a liquid reaction mixture (organic and/or aqueous phases) with carbon dioxide shows interesting positive effects on the reaction rate, the product selectivity, and the deactivation of a conventional supported metal catalyst. In some cases the use of both water and dense phase carbon dioxide serves as an effective reaction medium. In other words, these green solvents may act as reaction promoters. Possible roles of their actions are discussed. [ABSTRACT FROM AUTHOR]

Selective hydrogenation of acetophenone (AP) to 1-phenylethanol (PhE) was investigated over Rh/Al2O3 and Rh/C catalysts in 13 solvents including water and conventional organic solvents. Strong solvent effects on the overall rate of AP conversion were observed in different manners depending on the catalysts used. The conversion obtained is correlated with hydrogen-bond-donation (HBD) capability for Rh/C but with hydrogen-bond-acceptance (HBA) capacity for Rh/Al2O3. The solvent effects should result from interactions between the carbonyl group of AP and the solvent molecules through hydrogen bonding for Rh/C and from those between the solvent molecules and the catalyst surface for Rh/Al2O3 having HBD hydroxyl groups on its surface. Water is the most effective functional solvent in the selective hydrogenation of AP for C and Al2O3-supported Rh catalysts due to its high HBD capability (α) and low HBA capability (β), respectively. For the hydrogenation with Rh/Al2O3 in water, its large polarity/polarizability index (π*) may contribute to the high selectivity to PhE. [ABSTRACT FROM AUTHOR]

Chemoselective hydrogenation of water-insoluble aromatic nitro compounds can be achieved over Ni catalysts in a H2O–compressed CO2system at 35–50 °C without using any environmentally harmful solvent. The effective CO2pressure is much lower than the critical pressure of CO2. The hydrogenation of nitro group should be the rate-determining step. [ABSTRACT FROM AUTHOR]

Highlights: [•] The doping of NiO x can improve the photocatalytic activity of TiO2. [•] NiO x /TiO2 is active for photocatalytic H2 production from aqueous glycerol. [•] The catalytic performance of NiO x /TiO2 depends on calcination temperature. [ABSTRACT FROM AUTHOR]

Highlights: [•] CO formed on Pd surface retards the adsorption of phenol. [•] Cyclohexanone is preferentially adsorbed on Pd than CO and water. [•] The leaching of Pd occurs and the potential of Pd surface gradually changes in hot water. [•] The catalyst deactivation occurs rapidly in the presence of both dense phase CO2 and water. [ABSTRACT FROM AUTHOR]