Mwcnts Load Precious Metal Catalyst Preparation And Alpha, Beta Hydrogenation Of Unsaturated Aldehyde Selectivity

α,β-unsaturated aldehyde is an important chemical raw materials and intermediates in industrial production, its selective catalytic hydrogenation reaction is a hot topic in the field of catalytic research. The semi-hydrogenated products such as α,(3-unsaturated alcohol and saturated aldehyde are important fine chemicals and intermediates, especially in perfume industry and medicine manufacture. As two of the representative α, β-unsaturated aldehydes, studies on selective hydrogenation of cinnamaldehyde (CAL) and citral are particularly importance because their partial hydrogenation into ether unsaturated alcohol or saturated aldehyde is a critical step for the industrial production of many fine chemicals, especially perfumes and pharmaceutical intermediates. Therefore, the study of α, β-unsaturated aldehyde hydrogenation reaction not only has important theoretical significance, but also has a wide range of industrial application prospect.Considering unique physical and chemical properties of multi-walled carbon nanotubes (MWCNTs), such as the structure of pore channel, large surface areas, high stability and so on, the catalysts supported over MWCNTs can avoid the impact of diffusion and reduce the occurrence of side effects in liquid phase reaction. Liquid-reduction process was used to prepare multi-walled carbon nanotubes (MWCNTs) supported Pt catalysts (Pt/MWCNTs) and Pd catalysts (Pd/MWCNTs). Based on the intermolecular interactions between CO2and alcohols, CO2+trifluoroethanol (TFEOH) was used as a medium for the selectively catalytic hydrogenation of α, β-unsaturated aldehydes. The hydrogenation of CAL and citral is selected as a model reaction, and the effects of operating parameters including reaction time, CO2pressure, H2pressure, temperature, and different solvents on the activity and the product selectivity were investigated. We also tested the catalyst life, The main results of the present thesis are as follows:1. Selected four kinds of organic solvents, such as ethanol, trifluoroethanol, isopropanol and acetone. The volumetric expansion rates of them were investigated at different tempratures and at different initial volumes. The results showed that the trifluoroethanol can be used as a good solvent for the selectively catalytic hydrogenation reaction. In CO2, the expanding performances of organic solvents reduce with the increase of reaction temperature and polarity of solvent. In order to make the reaction system to be homogeneous phase, adding a small amount of appropriate solvent in CAL or citral can reduce the CO2expanding pressure.2. The reaction of CAL hydrogenation was evaluated over Pt/MWCNTs and Pd/MWCNTs catalysts. It is found that the Pt/MWCNTs catalysts exhibited high selective hydrogenation towards C=O bonds, showed the selectivity to cinnamyl alcohol (COL) of97.3%, and the conversion of CAL reached99.3%. However, it is found that the Pd/MWCNTs catalysts exhibited high selective hydrogenation towards C=C bonds, showed the selectivity to hydrocinnamaldehyde (HCAL) of91.3%, and the conversion of CAL reached98.6%. The small diameter of Pt or Pd grain over MWCNTs leads to high activity of catalysts, and the increasing of CO2pressure gives better hydrogenation performance for C=O bond than that for C=C bond.3. The selective hydrogenation of citral was investigated over Pt/MWCNTs catalyst, which was different from the selective hydrogenation of CAL. The effects of reaction time, reaction temperature, CO2pressure, H2pressure and kinds of solvents on the catalytic performance were studied. It is found that the reaction conditions had a great influence on the selectivity to hydrogenation product, such as citronellol and unsaturated alcohol. The studies on the selective hydrogenation of citral will provide experimental evidence for its further investigation.