Preparation of Magnetic Difunctional Catalysts,Characterization of Structure and Their Catalytic Performance for Methanol Catalysis Activity

Author:Shi Da

Supervisor:ji sheng fu

Database:Doctor

Degree Year:2017

Download:59

Pages:166

Size:19574K

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Compared with traditional gas phase catalysts,liquid phase reaction could process more reactants during the same time and improve the coversion of reactants and selectivity of products.However,the amount of the homogeneous catalyst in the liquid phase reaction is generally large,and the separation and recovery of homogeneous catalysts in the liquid phase after reaction is also a difficult problem.This leads to a huge waste of resources,and does not comply with the current advocated concept of green chemistry and energy efficient use.Moreover,some of the commonly used Lewis acid catalysts also cause the corrosion of the equipment,increase cost of operation and maintenance of equipment,and do not meet our requirements to maximize the economic benefits.Methanol,one of the simplest alcohols,is one of the most important chemical raw materials that can be used in energy as fuels or synthesis dye,perfume or explosive materials.In the transformation of Methanol catalysis,there are many high value-added chemicals include formic acid,DMM,MF,etc.However,the traditional preparation method has a long reaction process route with pollution and may cause reaction equipment corrosion seriously.For example,in the gas-phase conversion of methanol-to-methanol,methanol is oxidized to formaldehyde and then oxidized to formic acid.The feed concentration of methanol is low,and a large amount of gas is needed to circulate and the reaction selectivity is low.In the preparation of formic acid by liquid-phase methanol conversion,methanol is first converted to methyl formate and then to formic acid via hydrolysis.This process route is long,there is much wastewater discharge and the corrosion of the reaction pipe is serious.These preparation processes are time consuming with high cost.Once the high efficient catalyst is adopted,the pollution of the reaction can be reduced and the steps can be cut down,thereby strengthening the reaction process.In this paper,a series of catalysts with different loading amounts such as Au/TiO2,Pd/TiO2,AuPd/TiO2,AuAg/TiO2 and PdCu/Cu2 O were prepared.The structures of the bifunctional catalysts were characterized by scanning electron microscopy(SEM),energy dispersive spectrometer(EDS),high resolution transmission electron microscopy(HRTEM),X-ray diffraction(XRD),N2 adsorption/desorption and in situ infrared(FT-IR)The catalytic activity of these bifunctional magnetic catalysts was evaluated by the oxidation reaction.The effects of different reaction conditions on the catalytic activity of the catalysts and the repeatability of the catalysts were investigated.The selectivity and reaction mechanism of the catalysts for the oxidation of methanol were also studied.1.The Au/TiO2 catalyst with uniform particle size of about 4 nm was prepared by loading nano Au onto the mesoporous TiO2 carrier.At the same time,the catalyst could efficiently catalyze the oxidation of methanol to prepare formic acid.By optimizing the reaction conditions,the yield of formic acid can reach 29.1% at a certain temperature and pressure.The catalyst for the reaction has a very good stability,and then re-use 5 times;the yield of formic acid can still reach more than 25%.At the same time,the reaction mechanism was studied.It was concluded that methanol was first oxidized to formaldehyde by dehydrogenation reaction and then oxidized to formic acid.CO2 was the byproduct of the reaction,which was mainly obtained by oxidation of formaldehyde.At the same time,the conversion rate of methanol was 94.8% by using H2O2 as oxidant under the condition of optimization of reaction conditions.2.The Pd/TiO2 catalyst with uniform particle size at about 4 nm was prepared.At the same time,the catalyst could efficiently catalyze the oxidation of methanol and had some selectivity for the product,and could gradually change from the high selectivity of formic acid to the selective conversion of methyl formate high.By optimizing the reaction conditions,the reaction conversion rate can reach 25.8% and the selectivity of formic acid is 62.7% at a certain temperature and pressure,and the selectivity of methyl formate can reach 34.5%.The catalyst for the reaction has a very good stability,and then re-use 5 times;formic acid and methyl formate selectivity can still reach 60% and 30% or more.At the same time,the reaction mechanism was studied.It was concluded that methanol was oxidized to formaldehyde by formaldehyde and then oxidized to formic acid.The CO2 was the byproduct of the reaction,which was mainly obtained by oxidation of formaldehyde.The results are consistent.3.Compared to monometallic catalysts,the bimetallic catalysts have better catalytic activity,higher conversion rates,higher selectivity for methyl formate,and longer catalyst life.The particle size of AuPd/TiO2 and AuAg/TiO2 bimetallic catalyst is increased to about 6nm,but the structure does not change.At the same time,the catalyst can efficiently catalyze the oxidation of methanol and effectively improve the selectivity of the reaction to methyl formate The By optimizing the reaction conditions,the conversion of the reaction can reach 33.7% for AuAg/TiO2 at a certain temperature and pressure,while the selectivity of methyl formate can reach 34%,and the reaction is further improved with respect to the single metal.For the AuPd/TiO2 catalyst,the reaction product can be converted from formic acid to methyl formate,resulting in a certain degree of controllability for the methanol oxidation reaction product.Two kinds of bimetallic catalysts have good stability for the reaction,and the selectivity of formic acid and methyl formate is still stable after 5 times of repeated use.At the same time,through the previous research on the reaction mechanism,the reason why the bimetallic catalyst is promoted for the oxidation of methanol is analyzed.4.Preparation of PdCu/Cu2 O Catalyst by Pd/Cu-BTC Synthesis.The catalyst has a unique nanowire structure,while the metal nanoparticles can have a particle size of about 2 nm and exhibit excellent catalytic properties for the oxidation of methanol.In contrast to the mono-metal Pd catalyst,the bimetallic catalyst has a higher conversion rate of 37.8% for the reaction and 41.7% for the higher selectivity for methyl formate.Moreover,the life of the reaction is longer,more stable at high temperatures,and the yield of byproducts is lower.The five kinds of bifunctional catalysts prepared at the same time have two kinds of catalytic active sites,such as oxidation center and acid center,and the particle size is about 2-6nm.It is applied to the methanol oxidation reaction,and achieved very good results.Bifunctional catalyst,the original industrial two-step or even multi-step reaction is short as a one-step reaction,while the reaction of the product to show a certain selectivity,making the reaction of the product to a certain extent,control,and have a stable re-use perfornance,With excellent industrial application potential.