Preparation Of Au CNT Catalyst And Its Application In Benzyl Alcohol Oxidation

Benzaldehyde is widely used in industrial production,especially in in spice,pharmaceutical research,food additives and intermediates as other industrial products,Therefore,benzaldehyde has essential application value.In the production process of the factory,toluene is used to produce chlorinated compounds,and then benzaldehyde is obtained by hydrolysis in acidic or alkaline conditions.This method will produce more by-products,resulting in the reduction of the selectivity of benzaldehyde.Therefore,benzyl alcohol was selected as the reactant in the laboratory.Under the condition of catalyst,oxygen was continuously injected into the liquid phase to oxidize benzyl alcohol to benzaldehyde.This paper introduces a kind of high efficiency catalyst with simple preparation process and environmental protection,which is applied to the selective oxidation of benzyl alcohol,and probes into the catalytic performance of the catalyst.In this paper,a series of catalysts(Au/CNT)with different sizes of gold nanoparticles supported on carbon nanotubes(CNTs)were prepared by sol-gel anchoring method.The effects of different sizes of gold nanoparticles on the catalytic activity of catalysts for the oxidation of benzyl alcohol to benzaldehyde were studied.We have successfully prepared Au/CNT-A,Au/CNT-T_H,Au/CNT-T_L and Au/CNT-N catalysts with different sizes of gold nanoparticles.Then,the catalysts were characterized by different methods in order to study the catalysts.Four kinds of catalysts were applied to the oxidation of benzyl alcohol to benzaldehyde,and their catalytic activities were compared.Transmission electron microscopy(TEM)showed that the size of gold nanoparticles in the Au/CNT-A catalyst prepared by polyvinyl alcohol(PVA)was the smallest,about 4.9±2 nm.The gold nanoparticles were spherical and evenly dispersed on the surface of carbon nanotubes.The size of gold nanoparticles in the Au/CNT-N catalyst prepared without protective agent was the largest,about 21.98±3.7 nm.At the same time,the four catalysts were applied to the oxidation of benzyl alcohol.Under the conditions of 80℃,continuous oxygen injection and reaction time of 3 hours.The measured selectivity of Au/CNT-A catalyst to benzaldehyde is 70%,and the conversion rate of benzyl alcohol is 81%.This catalyst has the best catalytic performance.Then without changing the external conditions,the conversion rate of benzyl alcohol for the Au/CNT-N catalyst is 24%,and the selectivity to benzaldehyde is 82%,which indicated that the size of Au nanoparticles affected the catalytic performance of selective oxidation of benzyl alcohol.Finally,the conversion frequency(TOF)of the four catalysts were calculated.The TOF value of Au/CNT-A(TEM particle size=4.9 nm)was about 3.6 times that of Au/CNT-N(TEM particle size=21.9 nm)The number of converted benzyl alcohol molecules has a great influence.Then,a series of Au-Ni O/CNT catalysts were prepared by ultrasonic impregnation and sol-gel anchoring.Then,the effect of metal oxide(Ni O)doping on the oxidation of benzyl alcohol was studied.Au-x Ni O/CNT(x=2,4,8,12,16)catalysts with different molar ratios were prepared by changing the molar ratio of Au to Ni O.The XPS results show that the doping of nickel oxide(Ni O)adds lattice oxygen on the surface of the carbon nanotube support,and the content of oxygen-containing functional groups(C-O,O-C=O and C=O)increases significantly.Increased,the oxidation performance of benzyl alcohol is more important,and the oxygen storage/release capacity of the catalyst is improved,which plays a role in providing active oxygen in the reaction process.Transmission electron microscopy(TEM)showed that compared with undoped nickel oxide(Ni O),the doping of nickel oxide makes the size of gold nanoparticles smaller.The reason is to prevent the coalescence of gold nanoparticles during the preparation process.When the ratio is Au:Ni O=1:12,the diameter of Au-12Ni O/CNT catalyst gold nanoparticles(Au Nps)is about 2.6±1.3 nm.Under the condition of continuous oxygen gas at 50°C for 3 hours,the catalytic activity of Au-12Ni O/CNT is the best,the conversion rate of benzyl alcohol is up to 67.4%,the selectivity of benzaldehyde is up to 83.9%,and no nickel oxide is doped.In the case of(Ni O),the conversion rate of Au/CNT catalyst at 50°C is only 52.9%.The above analysis shows that the doping of Ni O not only affects the formation process of gold nanoparticles,but also affects the selective oxidation process of benzyl alcohol.