He Study On The Catalytic Performance Of Au/γ-Al₂O₃in The Direct Esterification Of Aldehyde With Alcohol

Esterification is one of the most fundamental transformations in organic synthesis. The product is widely used as important intermediates in organic chemistry. Traditionally, the reaction was performed between carboxylic acid derivatives and alcohols. However, because these reactions need harsh reaction conditions and seriously corrosion, a new method for the synthesis of ester attracts much attention recently. Although several transition metal catalysts have been reported in esterification reactions, the development of a catalytic method for the direct oxidative esterification of aldehydes with alcohols under mild and neutral conditions in the presence of heterogeneous transition metal catalysts is highly desirable for both economic and environmental reasons. In this study, we optimized the preparation conditions of Au/γ-Al2O3and use the catalyst for both the thermal catalytic and photocatalytic of esterification.1. The different kinds of impregnation-reduction method were used in the preparation of AU/γ-Al2O3. The major factors of catalytic activity were investigated by X-ray diffraction, Transmission electron microscopy, X-ray photoelectron spectroscopy, low temperature N2adsorption and so on. The results showed that the small and well dispersed gold nanoparticles which were prepared by the impregnation-reduction method with L-Lysine protected is the key to increase the catalytic performance for esterification of benzaldehyde. 2. The catalyst was used for the direct esterification of benzaldehyde with alcohol and had a good performance with the conversion of benzaldehyde was94.0%and the selectivity for ester was98.5%in mild conditions. The effects of supports, gold loading, reaction temperature and time for this reaction were studied. And we found the catalyst was difficult to reuse.3. The Au/γ-Al2O3was also used as a photocatalyst for the direct esterification of benzaldehyde with alcohol and had a good performance (the conversion of benzaldehyde was94.0%and the selectivity for ester was98.5%)in mild conditions. After reused for several times, the catalyst also have a good activity. The effects of light intensity and wavelength on photocatalytic direct esterification of benzaldehyde were studied. The results showed that light intensity and wavelength are important irradiation energy parameters and hence, they are the critical factors influencing the performance of photocatalyst in reactions. The visible light can make contribution to the activation energy decrease.