| Cinnamaldehyde is a kind of representative aromatic α,β-unsaturated aldehydes, and the selective hydrogenation reactions of cinnamaldehyde play important roles in the fine chemical industries and pharmaceutical industries. There exist C=O and C=C bonds in the molecular structure of cinnamaldehyde, and so the corresponding catalytic hydrogenation reaction maybe leads to the formation of 3-phenylpropyl aldehyde, cinnamylalcohol and 3-phenyl allyl alcohol. If the reaction continues, the 3-phenyl propyl alcohol was found finally. Among them, cinnamylalcohol has been widely used, which not only acts as a fixative and modifier in the essence, perfume and cosmetics production, but also is an important pharmaceutical material often used in the treatment of cardiovascular and cerebrovascular diseases and some tumor. However the C=C bond hydrogenation is easier than C=O bond on the thermodynamics, so the selectivity to form cinnamylalcohol is poor. In addition, the C=O and C=C bonds are conjugated with benzene ring in the molecule, so it is more difficult to control the selectivity of the C=O bond hydrogenation. Therefore, the selective hydrogenation reactions of cinnamaldehyde get more and more attentions.In recent years, in order to improve the selectivity of cinnamaldehyde hydrogenation reaction, proper catalysts, carriers, additives, reaction temperature, reaction time and other reaction conditions have been tested. At present, the metal catalysts play very important roles in many areas, such as petroleum, chemical industries, medicines. For example, Ru, Pd and Pt metals are often used in catalytic hydrogenation reactions, but they have different activity and selectivity. Moreover, the particle sizes and shapes of metal catalysts, and doped other elements to the metal catalysts also have obvious effects on the activity and selectivity. Some of existing literatures show that metal clusters have become hot due to their special structures, and special properties in the light, electricity, magnetic, mechanical.In this thesis, the selective hydrogenation reaction mechanism for cinnamaldehyde catalyzed by the Ptn(n=6,10,14,18) clusters were studied by the density functional theory. All of compounds were optimized at the B3LYP/6-31+G(d) level and the Lanl2 dz basis set for Pt. In addition, the effects of particle sizes and Co-doped Ptn clusters were taken into consideration. All results are as follows:Firstly, the pathway analysis: There are are three kinds of products about 3-phenylpropyl aldehyde(P1), 3-phenyl allyl alcohol(P2) and cinnamyl alcohol(P3) were found in the selective hydrogenation reactions catalysted by Ptn clusters and each product has two different pathways.Secondly, in the selective hydrogenation reactions of cinnamaldehyde catalysed by Pt6、Pt10、Pt14、Pt18 clusters, the required activation energy is P1>P2>P3 in the respective optimal reaction pathways, i.e. Ptn clusters are beneficial to the C=O bond hydrogenation.Thirdly, the selectivity is closely related to particle sizes of catalysts. Among them, the Pt14 cluster is the optimal particle size because of the lowest active energy to form the P3.Fourthly, the Co-Pt5 cluster is formed by the Co metal doping Pt6 cluster, and the pathways of selective hydrogenation reaction catalysed by the Co-Pt5 cluster are consistent with non-doped Pt6 cluster. Furthermore, there have two different pathways to form the P1, P2 and P3, respectively, but the P3 required activation energy is the lowest. Compared with non-doped Pt6 cluster, the activation energy is lower in the selective hydrogenation reaction catalysed by the Co-Pt5 cluster. Due to the synergetic effects between the Co and Pt, it is favour of the C=O bond hydrogenation. |
PDF Full Text Request