Papers by Keyword: Selective Hydrogenation

Abstract: Synthesis of zingerone (4-(4-hydroxy-3-methoxyphenyl)-2-butanone) has been done. The first step was to synthesize the compound (4-(4-hydroxy-3-methoxyphenyl)-3-buten-2-on) through a cross aldol condensation reaction between vanilin:acetone mol ratio of 1:5:5, for 5 hours in high yields (97%). The second step was the selective hydrogenation of (4-(4-hydroxy-3-methoxyphenyl)-3-buten-2-on) with NiCl₂•6H₂O-NaBH₄ catalyst in mild condition. Based on the FT-IR, ¹³C-NMR and ¹H-NMR and GC-MS analyses, the synthesis of zingerone has been successfully synthesized by selective hydrogenation reaction with 80% yield.

Abstract: Fe_xO_y@C nanocomposites were synthesized and used as carriers for depositing Pt nanoparticles. Catalytic properties of the nanocomposites were investigated for the hydrogenation of p-chloronitrobenzene at room temperature and balloon hydrogen pressure. The catalyst Pt/Fe_xO_y@C was extremely active for the hydrogenation of p-chloronitrobenzene. Completely conversion of p-chloronitrobenzene was achieved with a selectivity of 99.7 % in ethanol-water mixture in a reaction time of 40 min. Moreover, it can be reused four times without loss of any activity.

Abstract: The Ir/AlO(OH) catalyst was prepared by sol-gel method and used for selective hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroniamine (p-CAN). The mechanism of p-CNB hydrogenation over the catalyst was discussed. The hydrogen bond between the surface hydroxyl groups of the catalyst and the nitrogen present in p-CNB facilitated the hydrogenation of nitro group. On the other hand, the formation of hydrogen bond between the hydrogenation product and water promotes the rapid desorption of the hydrogenation product on the surface of the catalyst. Thus the activity and selectivity were greatly promoted.

Abstract: Several representative solvents classified in three categories: 1) aprotic apolar solvents: 2) protic solvents; 3) aprotic polar solvents were chosen to investigate the effect on the catalytic activity and selectivity for the selective hydrogenation of 3,4-dichloronitrobenzene (3,4-DCNB) over Pd/C catalyst. The solvent polarity increases the hydrogenation rate apparently, but also increases the selectivity to 3-chloroaniline and 4-chloroaniline from dehalogenation reaction. The solvents with the high polarity and hydrogen-bond donation capability can generate the strong interaction and the H-bond with nitro group of 3,4-DCNB, and then promote the activation and polarization of nitro group. However, on basis of the result of water as solvent, the higher hydrogenation rate in polarity solvents, to a larger extent, may be attributed to the increase of the amount of reactive chemisorbed hydrogen resulting from the dissociative chemisorption of aprotic polar solvents over the activated metal surface. At the same time, this is why the selectivity to 3-chloroaniline and 4-chloroaniline from dehalogenation reaction increase obviously with the increase of solvent polarity, because the amount of reactive chemisorbed hydrogen on the catalytic activated sites exceeds the needs of nitro group reduction and then surplus hydrogen reacts with the C-X bond.

Abstract: Cu-Zn-Al catalyst was modified by the additives such as Ni and Mn, and the prepared catalyst was employed in the selective catalytic hydrogenation of cinnamaldehyde. The results showed that the addition of Ni could improve catalytic activity significantly, moreover, the improving effect was highest when Zn was replaced by Ni, simultaneously leading to excessive hydrogenation. The Cu-(5%)Mn-Zn-Al catalyst exhibited a higher selectivity of 93.6% for C = O bond to cinnamyl alcohol and hydrogenation activity of 33.0% conversion at 130°C under 1.0 MPa of H2 pressure with the reaction time of 1 h. TPR and XRD characterization showed that Mn promoter was favorable for the growth of Cu0 fine grains on the surface of catalyst, which not only led to steric effect which improved the selectivity for cinnamyl alcohol, but also reduced the numbers of active centers, consequently decreased the reaction rate.

Abstract: The selective hydrogenation of 4,4'-methylenedianiline(MDA) over Ru/γ-Al2O3 was investigated in the presence of diamine and base. Under the optimum conditions: the reaction temperature of 448K, H2 pressure of 1100 psig , and reaction time of 5h, the conversion of 4,4'-methylenedianiline was close to 100% and the selectivity to trans-trans isomer of 4,4'-diamino-dicyclohexy was less than 20%.

Abstract: The nano-Ru/[Bmim][BF₄] catalyst was prepared for benzene selective hydrogenation in 1-n-butyl-3- methylimidazolium tetrafluoroborate [Bmim][BF₄] by chemical reduction method. TEM analysis of these nanoparticles sho wed the monodisperse Ru⁰ particles which were prepared by positive dropping method dispersed in the ionic liquids with diameters less than 5nm. The Ru⁰ particles which were prepared by reverse dropping method agglomerated with diameters more than 10nm. KBH₄ was the suitable reductant. The optimum loading of Ru was 1.5%. The hydrogenation activity of Ru/ [Bmim] [BF₄] was high and the selectivity of cyclohexene was very low. Selectivity of cyclohexene was only 14.5% at 27.3 % benzene conversion.

Abstract: By pretreatment of Pt/CeO₂ catalysts with high temperature reduction and subsequent low temperature reoxidation, the concentration of Ce³⁺ species in the Pt/CeO₂ catalysts could be adjusted, while at the same time the Pt particle size remained constant. Thus the pure effect of Ce³⁺/Ce⁴⁺ couples on the selective hydrogenation of crotonaldehdye could be explored. The investigation provided direct proofs supporting that Ce³⁺ species favors the crotyl alcohol selectivity.