Preparation Of Hydrophobic Catalysts And Their Application In Oxidative Esterification Of Aldehydes

Esters, extremely important fine chemical raw materials and organicintermedium, are mainly used for the production of coatings, medicines, foods,flavors and polymers. The traditional esters synthesis routes have the shortages likelong process flow and serious causticity to the equipments and so on. The method thatsingle-step oxidative esterification of aldehydes to esters has a broad applicationprospects with advantages such as short reaction time, mild reaction conditions andsimple posttreatment. In this process, development of catalysts with high efficiency isthe key factor.Firstly, catalysts with different supports were prepared by the incipientimpregnation method; their activities were evaluated and the catalysts werecharacterized. The results indicate that catalysts with hydrophobic carriers have highercatalytic activities. BET results showed that SDB(X-5) has a large surface area, andgood mechanical properties, therefore, SDB(X-5) is the best carrier. The effects ofpreparation conditions on the catalytic reactions were investigated and the resultshowed that reduction temperature200℃, reduction time of10h were the optimum.The effects of co-catalysts on the catalytic performance were studied. The bimetallicand trimetallic catalysts were prepared with Pb, Bi, Fe, Cu as the second (or third)metal. The evaluate result indicated that addition of Pb, Bi to monometallic catalystsimproved the catalytic performance obviously, and the optimum catalyst wasPd3Pb0.6Bi1.5/SDB(X-5).TEM result indicates that the addition of Pb and Biameliorated the metal distribution on the supports. XPS result showed that theelectron of Pd transferred to promoters in this tri-metallic catalyst. XRD resultshowed that a strong interaction between Pd-Pb and Pd-Bi, leading to the formation oftwo binary alloys composed of Pd3Pb and PdBi, which were favorable for improvingthe activity and stability of the catalyst.Secondly, the catalytic activities of Pd3/SDB(X-5) in the oxidative esterificationof different type of aldehydes were studied and benzaldehyde was chosen as a testsubstrate to optimize the reaction conditions of temperature, time and the molar ratioof aldehydes with alcohols. The results indicated that this catalyst has better catalyticactivities in the oxidative esterification of aliphatic aldehydes and the aromaticaldehydes with electron-donating substituents.Finally, adsorptions of water in different catalyst supports have been studied by molecular simulation method. Based on the data of adsorption capacity and isostericheat, we get the information about the relationship between the hydrophobicity ofsupports and catalytic activity on the micro level.