Preparation Of Supported Catalysts And Study On Catalytic Performance Of Methanol Oxidation

Due to a serious excess of methanol production in recent years,the development of methanol downstream products has become an important solution to the problem of methanol excess.Therefore,by methanol catalytic oxidation reaction,researchers convert the methanol into methyl formate,methyl acetal and formaldehyde and other methanol downstream products which can improve the added value of methanol and provide guidance for the oxidation of small molecule alcohols.At present,the oxidation of methanol is mostly carried out by gas phase oxidation,and the research of liquid phase oxidation is rarely reported.The study found that the catalyst is the key to affect the oxidation of liquid phase methanol.The catalyst needs to have an oxidizing site and an acidic site.Therefore,we used the bi-functional catalysts to catalyze methanol directly to methyl formate.The combined effect of acidity and oxidability on the surface of the catalyst can increase the conversion of methanol and the selectivity of methyl formate.Bi-functional Catalysts Au/ZrO2,Pd/ZrO2,and Au-Pd/ZrO2 were prepared by sol-gel method.These catalysts were characterized by XRD,TEM,XPS,NH3-TPD,respectively.The effects of the time,the temperature,the oxygen pressure,the mass of the catalyst,the ratio of the loading metal,the solvents and the carrier on the catalytic methanol performance were studied.The results are as follows:(1)The apparent peaks of ZrO2 can be observed by XRD characterization of Au/Zr02 catalyst,but the diffraction peaks of Au nanoparticles are not observed.We can confirm the loaded metal is Au(0)by XPS characterization.The metal Au can be seen on the carrier by TEM characterization.The NH3-TPD characterization indicates that the acidity of catalyst was mediate strong one,which is also consistent with the excellent performance of the catalyst in the catalytic oxidation of methanol.When the reaction time was 7 h,the reaction temperature was 150?,the initial oxygen pressure was 2 MPa,0.05 g 2wt%Au/Zr02 catalyst was used,and the reaction was solvent-free reaction.The conversion of methanol was 33.35%and the selectivity of methyl formate was 39.45%.when 2%Au/Zr02 was reused 4 times,the conversion rate declined slightly,which was related to the agglomeration and loss of Au particles.(2)The apparent peaks of Zr02 can be observed by XRD characterization of Pd/Zr02 catalyst,but the diffraction peaks of Pd nanoparticles were not observed.We can confirm the loaded metal is Pd(0)by XPS characterization.The metal Pd can be seen on the carrier by TEM characterization.The formation of Au-Pd alloy on bimetallic catalysts can be conformed by XPS characterization.The overall acidity of the bimetallic catalyst is stronger than that of the single metal.When the reaction time was 6 h,the reaction temperature was 140? and the initial oxygen pressure was 2 MPa.0.05 g 1wt%Pd/ZrO2 catalyst was used;the reaction was solvent-free reaction.The conversion of methanol was 35.51%,and the selectivity of methyl formate was 48.32%.After 1wt%Pd/ZrO2 was used 5 times,the conversion and selectivity began to decrease,which was related to the agglomeration and loss of Pd particles.The optimum loaded Au amount of bimetallic Au-Pd/ZrO2 catalyst which containing 1wt%Pd was 2wt%.The conversion of methanol was 48.55%and the selectivity of methyl formate was 50.26%,when 2wt%Aulwt%Pd/ZrO2 catalyst was used in the same condition above.And this catalyst can be reused for 5 times.It showed that the bimetallic Au-Pd/ZrO2 catalyst has a better performance than the monometallic catalyst.2wt%Au1wt%Pd/ZrO2 is the optimum catalyst in this thesis.