The conjugated C=C and C=O bonds are present inα,β-unsaturated aldehydes molecules. The products ofα,β-unsaturated alcohols, which are produced by the selective hydrogenation of C=O bond inα,β-unsaturated aldehydes molecules, are important fine chemicals and intermediates especially in perfume industry and medicine manufacture. However, the selective hydrogenation of C=O bond is different from that of C=C bond because of the conjugated system between C=C and C=O bonds. Therefore, research on the selective hydrogenation ofα,β-unsaturated aldehydes is of great importance in industrial applications and theoretical aspects. Cinnamaldehyde (CMA) is a typical representative of a, P-unsaturated aldehydes, and it is easier for the hydrogenation of C=C group than that of C=O group in CMA molecules. Usually, by means of changing the specific structure of catalysts, the C=O bond can be preferentially adsorbed and activated to react with the adsorbed hygrogen, or the C=C bond are strongly adsorbed to become less activated in order to achieve selective hydrogenation efficiently. Based on the rule of selective hydrogenation of CMA, in this Master's thesis, a series of supported Pt and Pt-M (Co, Ni, Cu,Fe, Mn) catalysts are prepared and mainly investigated their properties for the selective hydrogenation of C=O bonds in CMA molecules in the reaction system of ethanol/water. Some specific conclusions drawn from this work are as follows:1. The selective hydrogenation properties of CMA have been studied over Al2O3, ZrO2, TiO2, carbon nanotubes (CNTs) and active carbon (AC) supported Pt catalysts in the reaction system of ethanol/water. The results show that the catalytic activity of catalysts and the selectivity of CMA to cinnamyl alcohol (CMO) are both improved when the volume ratio of ethanol/water is 15/5-8/12. Under the conditions of 70℃,2 MPa H2,2 h and ethanol/water 15/5(mL/mL), the conversion of CMA and the selectivity of CMA to CMO reach 94.3% and 90.7% respectively over the Pt/TiO2 catalyst. And no production of aldol condensation and polymers are found. Under the conditions of 2 MPa H2,2 h and 20 mL water, the conversion of CMA and the selectivity of CMA to CMO reach 79.4% and 73.2% respectively over the Pt/ZrO2 catalyst, which is of great importance in reducing the use of organic solvent and realizing the process of green catalysis.2. The effect of transition metal (Co) doping on the selective hydrogenation properties of CMA over different supported Pt-Co catalysts are investigated in the reaction system of ethanol/water. The results show that a proper amount of Co improves the selective hydrogenation of C=O bond thus increasing the catalytic activity of these supported Pt catalysts and the selectivity of CMA to CMO. The Pt-Co/TiO2 (the Pt and Co content is 0.5 and 0.2 wt.%, respectively) catalyst exhibits the highest hydrogenation selectivity for C=O bond. Under the conditions of 70℃,2.0 MPa H2, 2.0 h and ethanol/water 15/5(mL/mL), the conversion of CMA and the selectivity of CMA to CMO reach 94.4% and 92.0% respectively. Under the conditions of 70℃,2.0 MPa H2 and 40 min, the Pt-Co/ZrO2 catalyst still exhibits high catalytic activity, 100% for the converision of CMA and 69.2% for the selectivity of CMA to CMO are obtained in water solvent.3. The effect of transition metals (Co, Mn, Cu, Ni and Fe) doping on the selective hydrogenation properties of CMA over Pt/ZrO2 catalyst are investigated systematically. The addition of Co, Ni and Fe improves the catalytic activity of Pt/ZrO2 catalyst. And the addition of Co, Fe and Mn are favorable for the selective hydrogenation of C=O bond while Ni is in favor of selective hydrogenation of C=C bond. Under the circumstances of 70℃,2.0 MPa H2,1.0 h and ethanol/water 12/8(mL/mL), the conversion of CMA and the selectivity of CMA to CMO reach 998.5% and 5.8% over the Pt-Fe/ZrO2 catalyst, which is one of the best results reported in literature at present.4. The influence of preparation method for ZrO2, reducers for catalysts and reaction conditions on the selective hydrogenation properties of CMA over Pt-Co/ZrO2 catalyst has been studied systematically. The results show that the catalytic activity is not only in relation to the number of activated hydrogen and the reductibility of PtOx species, but also in connection with the texture properties of the supports. The hydrogenation activity of Pt catalysts over the same carrier is mainly concerned with the texture properties of the support and those with high BET area and large pore size are favorable for the dispersion of active metals, as well as the adsorption of reactant molecules. These properties significantly improve the hydrogenation activity of catalysts. The choice of KBH4 for catalyst reducers can improve the catalytic activity and the selectivity of CMA to CMO resulting from the synergistic effect of Pt-Co-B. Further hydrogenation of phenylpropyl aldehyde (HCMA) and CMO mainly produces the product of phenylpropyl alcohol (HCMO). Simultaneously, increase of temperature is benefit for the selective hydrogenation of C=C bond in CMA molecules, and the introduction of surfactants plays no vital role in promoting the catalytic activity and the selectivity of CMA to CMO. |