Font Size: a A A

Investigation On CeO2 Catalyst In The Hydrogenation Of Benzoic Acid To Benzaldehyde

Posted on:2009-08-27Degree:DoctorType:Dissertation
Country:ChinaCandidate:M B ChongFull Text:PDF
GTID:1101360242495634Subject:Chemical Engineering
Abstract/Summary:PDF Full Text Request
Benzaldehyde is one of the most important aromatic aldehyde in chemical industry, which is mainly used for the manufacture of pharmaceuticals,plastic additives,perfumes and flavors.Nowadays,it is very important to develop green process of manufacturing benzaldehyde.Because benzaldehyde is the partial oxidation intermediate of oxidizing toluene and it is easily over oxidized to benzoic acid.Benzoic acid is both safe to people and acquirable.The method of hydrogenation from benzoic acid to benzaldehyde,which sprung up in the 1990's,is recognized as a promising commercial scale process for its simple process,high selectivity and environmental friendly 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.And the rare CeO2,which is abundant in our country,was selected to be favorable for the reaction.Then further investigation is focus on CeO2 catalyst,and some results were acquired as follows:(1)The CeO2 catalysts which are prepared by different methods show different performances to this reaction.The catalyst prepared from ammonium cerium nitrate with appropriate condition showed excellent catalytic activity.Besides,benzoic acid conversion of 99%and benzaldehyde selectivity of 95%were acquired at optimum reaction conditions based on the catalyst calcination at 550℃,so did the catalyst prepared at 600℃.All kinds of catalysts were characterized by XRD,BET,SEM,FTIR and NH3-TPD methods,and conclusions were drawn in the end.The catalyst prepared at lower calcination temperature shows high catalytic activity than the one prepared at higher temperature,because it has larger specific surface area,smaller average crystalline size,better dispersion as well as more weak surface acid sites and less strong surface acid sites.In addition,ZrO2,ZnO and oxide of Mn also show high catalytic activity to this reaction.(2)Catalysts were found deactivated with the time on stream.The catalyst prepared by lower calcination temperature shows the better catalytic stability,however the one prepared at higher temperature deactivates significantly.Both fresh and deactivated catalysts were characterized by BET,XRD,SEM,element analysis,TG/DTA and FTIR methods.The results reveal that the most important factor which induces catalytic deactivation is benzoic acid coking on surface acid sites of the catalyst.Two kinds of existed coke were revealed,which can be eliminated by air at no less than 410℃. Meanwhile,part of crystalline disaggregation and increase of crystalline size are also due to the catalysts' deactivation.(3)Catalytic performances of deactivated catalysts were regenerated by eliminating the coke by air at 450℃.Different kinds of catalysts show different regeneration performances.The catalyst prepared at low temperature shows the better regeneration performance and it can be used repeatedly,which is important to its commercial application.The regenerated catalyst showed inferior catalytic performance to the fresh one.Part of crystalline disaggregation and increase of crystalline size happened to CeO2 catalyst in several times of regeneration,which were responsible for inferior performance and irreversible deactivation.The effect of crystalline disaggregation was more significant than that of increase of crystalline size.Moreover,the result of XPS characterization indicates that catalyst deactivation was also due to the decrease of cerium concentration in the Ce3+state.(4)Catalytic performance of loaded catalyst onγ-Al2O3 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,etc.The catalyst prepared at 600℃based on coprecipitation method loaded with 40%CeO2 showed the best performance,whose activity approached pure CeO2 at appropriate reaction conditions.Furthermore,the loaded catalyst had even more excellent catalytic stability than that of pure CeO2 both on activity and selectivity in 30 h on stream.But the conversion of benzoic acid declined significantly after 30 h on stream.
Keywords/Search Tags:Benzoic acid, Hydrogenation, Benzaldehyde, CeO2, Reaction Mechanism, Deactivation, Regeneration
PDF Full Text Request
Related items