| Summary: | 碩士 === 桃園創新技術學院 === 材料應用科技研究所 === 101 === The Ag-Co catalysts were prepared by chemical reduction with sodium borohydride. Physical and surface properties of catalysts were characterized by techniques of BET, XRD, TGA, DSC, SEM-EDS, TEM and AFM. The catalytic behaviors of catalysts were explored by the selective hydrogenation of cinnamaldehyde in liquid phase. The factors affecting the activity and selectivity of catalysts included the preparation conditions of catalysts, reaction conditions, phenomena of overall hydrogenation and promoter effect. The Ag catalyst was much less active than CoB under the basis of same metal content. Replacing a part of Ag by Co during the preparation could promote significantly the activity of Ag catalyst. The optimal molar ratio of Ag/Co in Ag-Co catalysts was 6/4. Ag-Co(6/4) catalyst was not only as active as CoB catalyst, but also the selectivity to cinnamyl alcohol (unsaturated alcohol) was higher under the same conversion.
Silver itself has good activity in hydrogenation. The main reason for the low activity of Ag catalyst resulted from its low value of surface area, owing to the aggregation of silver metal. Replacing a small amount of Ag in catalyst by Co could significantly reduce the particle size of Ag, increase the surface area of catalyst, and the thermal stability was better than those of CoB and Ag catalysts. Ag-Co(6/4) catalyst could effectively hydrogenate cinnamaldehyde to unsaturated alcohol under 120 C and 120 psig. The adsorption strength of cinnamaldehyde molecules on Ag catalyst was much less than those on Group VIII metals. Therefore, the adsorption strength of the C=O bond with strong dipole was much greater than the C=C bond, the C=O bond was thus predominately reduced to form cinnamyl alcohol. A high selectivity of unsaturated alcohol about 93% was reached at the complete conversion over Ag-Co(6/4).
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