Preparation of l-phenylalaninol with high ee selectivity by catalytic hydrogenation of l-phenylalaninate over Cu/ZnO/Al2O3 catalyst
The Cu/ZnO/Al2O3 catalyst for hydrogenation of L-phenylalaninate to L-phenylalaninol was prepared by a co-precipitation method, and characterized by XRD, low-temperature N2 adsorption, H2-TPR, N2O chemisorption and ICP-AES. The results show that the physicochemical properties of the catalyst are greatly affected by the ZnO amount, and that the exposed copper surface area, dispersion of CuO and BET surface area of the Cu/ZnO/Al2O3 catalyst (Cu/Zn/Al = 1.0 : 0.3 : 1.0) reach the largest. The chemoselectivity of L-phenylalaninol is changed with ZnO amount in the Cu/ZnO/Al2O3 catalyst, and when Cu/Zn/Al = 1.0 : 0.3 : 1.0, the catalyst exhibits higher catalytic performance and chemoselectivity to L-phenylalaninol. Furthermore, the effect of temperature, pressure, reaction time and the molar ratio of catalyst to ester on the catalytic hydrogenation of L-phenylalaninate were investigated. When the catalytic hydrogenation of L-phenylalaninate was operated at 110 °C and 4 MPa of H2 for 5 h, the yield of L-phenylalaninol can reach 69.2 %, and its ee selectivity is 99.84 %.