Study On Preparation Of Benzaldehyde From Cinnamaldehyde Catalyzed By ZnO

Benzaldehyde,second only to vanillin in quantity and with an annual demand as high as 7,000 tons,is also an important chemical raw material and has been used in drug synthesis,food processing,cosmetics and other fields.As consumers pay more and more attention to green food,natural benzaldehyde is valued and represents good market competitiveness.Cinnamaldehyde is abundant in Guangxi and Hainan in China.In this paper,using cinnamaldehyde as raw material,transition metal oxide as catalyst and clean oxygen as oxidant,a green and efficient method for preparing benzaldehyde by oxidizing cinnamaldehyde was established.The main experimental tests,various characterization methods and in situ infrared analysis methods to study the oxidation reaction,can draw these conclusions:Firstly,a series of transition metal oxides were prepared and used to catalyze the selective oxidation of cinnamaldehyde by oxygen to prepare benzaldehyde.The effects of roasting temperature,roasting time,reaction temperature,reaction time,oxygen pressure,amount of catalyst and reaction temperature on the preparation of benzaldehyde by Zn O catalytic oxidation of cinnamaldehyde were investigated.The properties and states of the catalyst was analyzed by XRD,FTIR and TG-DTG.Under the optimum conditions,the selectivity of benzaldehyde reached 69%.The reusability of the catalyst was also investigated.The results showed that the main reasons for the deactivation of the catalyst were the adsorption and blockage of the reactants and reaction products on the surface and in the pores of the catalyst,and the catalyst was carbonated and hydrated.In addition,through GC,GC-MS analysis of the reaction products and literature review,we proposed the possible mechanism of this catalytic reaction.First,cinnamaldehyde and oxygen were converted into primary oxides,then into relatively stable secondary oxides,and finally benzaldehyde,benzoic acid and ethyl benzoate were generated.Secondly,in order to improve the activity of the catalyst,modified Zn O with some transition metals,and found that Zr-Zn O showed the best benzaldehyde selectivity,up to 86%.Compared with other catalysts,Zr-Zn O catalyst has better structure and stronger alkalinity,which is beneficial to improve the selectivity of benzaldehyde.Then we used XRD,XPS,FT-IR,TG-DTG,N2-adsorption and desorption characterization methods to analyze the physical and chemical state of the catalyst.Found that Zr doping can reduce the crystallinity of Zn O,improve the specific surface area of Zn O,increase the pore volume of Zn O,reduce the outer electron density of Zn,and enhance the surface alkalinity of Zn O.Finally,in order to study the acid-base of Zn O,Ce-Zn O,La-Zn O,Co-Zn O and Zr-Zn O surfaces,investigated the adsorption and desorption of three probe molecules,namely nitrobenzene,pyridine and trichloromethane,on their surfaces in an in situ diffuse reflection infrared device.The competitive adsorption of CO2 and O2 on Zr-Zn O and the adsorption of cinnamaldehyde on Zr-Zn O were studied.The results showed that Zr-Zn O catalyst had the strongest alkalinity,and its adsorption capacity for O2 was better than other catalysts.Cinnamaldehyde can adsorb on the catalyst surface stably in the oxygen environment.