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Studies on the Preparation and Asymmetric Hydrogenation of Platinum-based Bimetallic Catalysts

Author: HeNianZhi
Tutor: XiaoMeiTian;ZhangXueQin
School: Huaqiao University
Course: Chemical processes
Keywords: cinchonidine asymmetric hydrogenation ethyl2-oxo-4-phenylbutyrate heterogeneous catalysis platinum catalyst bimetallic catalyst
CLC: TQ426
Type: Master's thesis
Year: 2013
Downloads: 1
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Abstract


Cinchonidine modified Pt/γ-Al2O3catalysts exhibit excellent properties in theenantioselective hydrogenations of prochiral ketones. Asymmetric hydrogenation ofethyl2-oxo-4-phenylbutyrate to ethyl （R）-2-hydroxy-4-phenylbutyrate（EHPB）, Theproduct is a key intermediate for the synthesis of angiotensin converting enzymeinhibitors（ACEI）. In Master’s thesis, a series of γ-Al2O3supported Pt and Pt-M（Ni,Co, Cr, Ru, Ir） catalysts are prepared and investigated their properies for the theenantioselective hydrogenation of EOPB. Some main conclusions drawn from ourwork are follows:（1） A series of catalysts PVP-Pt/γ-Al2O3were prepared by different reductionmethods （ethanol, HCHO, HCOONa, and NaBH4） in the presence ofpolyvinylpyrrolidone （PVP） as stabilizer, the catalytic performance for asymmetrichydrogenation of ethyl2-oxo-4-phenylbutyrate was tested. The catalyst prepared byusing NaBH4as reducing agent showed the best overall performance. The effect ofvarious catalyst preparation conditions, such as reduction temperature, NaBH4concentration, the medium in which reduction was carried out, PVP/Pt mole ratio andreaction solvent and time was also investigated. Optically pure （R）-EHPB could beobtained with100%yield and76.8%e.e. when catalyst was prepared at0oC using0.5mol/L NaBH4in a medium of ethanol.（2） Pt/γ-Al2O3catalyst and Pt-M（Ni, Co, Cr）/γ-Al2O3bimetal catalysts wereprepared under optimum reduction conditions of PVP-Pt/γ-Al2O3catalyst. Heattreatment, Pt/M mole ratios, solvent and amount of cinchonidine was tested in theasymmetric hydrogenation of EOPB. It is found that the heat treatment increase Ptparticles size and enhance catalytic performance. The catalytic acitivity of Pt-Mcatalysts would decreases with M loading. XRD、TEM、XPS and H2-O2titrationanalysis showed strong interactions exist between Pt and M metal species on thecatalyst surface. M were virtually inactive and acted as a site blocker, whichdecreased the surface Pt sites and hindered the formation of the bulky transitioncomplex between the reactant and the chiral modifier and the loss in activity and selectivity.（3） Pt/γ-Al2O3catalyst and Pt-M（Ru, Ir）/γ-Al2O3bimetal catalysts were preparedby impregnation、calcination、hydrogen reduction in high temperature, Pt/M massratios, solvent and reaction temperature was tested in the asymmetric hydrogenationof EOPB. Both Ru/γ-Al2O3and Ir/γ-Al2O3catalysts show inferior catalyticperformance to Pt/γ-Al2O3catalysts in this reaction. TPR、XPS、XRD、UV-Vis、benzene/ethanol-TPDanalysis results showed cinchonidine is adsorbed on Pt, Ru andIr via the quinoline moiety approximately parallel to the metal surface by π-bondingand an additional interaction of the alkaloid molecule with thesurface occurs athydroxy oxygen atom C9. The former strength of force: F（Pt）>F（Ir）>F（Ru）; latterstrength of force: F（Ru）>F（Ir）>F（Pt）, which would lead to different adsorptiongeometry of quinuclidine on metallic surface. The difference adsorption geometrybetween the three metals induces the different catalytic results in the asymmetrichydrogenation of EOPB.

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