Study On Supported And Modified Of CeO₂ Catalyst In The Hydrogenation Of Benzoic Acid To Benzaldehyde

Benzaldehyde is an important kind of aromatic aldehyde in chemical industry as an essential chemical resource to produce aromatic chemicals, medicines, plastic additives and cosmetic preservatives. Nowadays, the development of benzaldehyde production is quite significant. Thus, a bunch of methods come into being as the times require. It is deemed that the method of hydrogenation from benzoic acid to benzaldehyde, which sprung up in the 1990s, has a bright future because of its accordance with the requirements of green chemical technology.Basic theory investigation of catalysts is recognized as the challenging theme on hydrogenation from benzoic acid to benzaldehyde. Many kinds of catalysts have been studied respectively in this dissertation. CeO₂, which is abundant in our country , have excellent activity for hydrogenation from benzoic acid to benzaldehyde. However CeO₂ is expensive , easily to coke and the catalytic stability isn't good enough. So further investigation on supported and modified CeO₂ catalyst are needed, and some results were acquired as follows.A series of CeO₂/Al₂O₃ catalysts were prepared by co-precipitated and impregnation methods and investigated for hydrogenation of benzoic acid to benzaldehyde. It was found that the catalyst preparation method as well as the CeO₂ loading had significant influence on the catalytic activity. The catalyst prepared by co-precipitation method, with 40% CeO₂ loading, precipitated above pH=9 and calcined at 600℃showed the best performance, on which the conversion of benzoic acid was 98.4 % and the selectivity of benzaldehyde was 93.7%. Catalysts prepared by co-precipitated method were found deactivation due to coke formation and could mainly be regenerated by eliminating the coke at suitable temperature by air. The catalysts were characterized by BET, XRD, SEM methods. Catalyst prepared by the coprecipitation method is even more excellent than that prepared by impregnation method, because the catalyst prepared by the coprecipitation method has larger specific surface area, smaller average crystalline size and better dispersion.Modified CeO₂/γ-Al₂O₃ catalysts with 40% CeO₂ loading by different amount of Cu,Zn,La,Mn,K was tested. Cu,Zn with the enhancement of redox is harmful for improving the catalyst activity. Catalyst with 10%La loading can substantial improves the activity ,but high amount lead to high cost. Mn improves catalyst activity to a certain extent, the amount is not important to the effect. Catalyst with 2%K loading have excellent effect, and the catalyst characterization of XRD, NH₃-TPD show 2%K have little effect on crystalline structure, but greatly reduced strong surface acid sites.Catalytic stability of catalysts was inspected. CeO₂/γ-Al₂O₃ catalysts with 40% CeO₂ loading stability is better of CeO₂, it was found deactivated with the time on stream after reacted for 42h. After modification, Ce(30%)-Mn(20%)-K(2%)/γ-Al₂O₃catalyst showed the best performance, on which the conversion of benzoic acid was above 99% and the selectivity of benzaldehyde was about 95.5%. It was keeping acticitive after reacted for 102h. Catalysts were characterized by TG/DTG method, the result show the deactivation of catalyst during redox process can be ascribed mainly to the coke formation. The amount of coke of 40%CeO₂/γ-Al₂O₃ catalyst is 4.6%, which is much more of modified catalyst of 3.56%. And the coked temperature is lower too. Meanwhile, the crystallite size increases along with the reaction progresses, which is also have affect to the activity.