Preparation And Performance Of Nano-gold Catalyst For Oxidative Esterification Of Methacrolein

Methyl methacrylate（MMA）is an extremely important monomer of organic polymer-polymethyl methacrylate（PMMA,also known as organic glass）.PMMA is widely used in construction,instrumentation,national defense and military industry,transportation,daily chemical products,and other fields.It is also widely used in latex paint,water-soluble coatings,and other fields.At present,the main process for producing MMA is the acetone cyanide method,but this method uses highly toxic raw material hydrocyanic acid,which poses a serious pollution risk.In recent years,starting from C4 raw materials,MMA has been produced through a series of oxidation and esterification reactions,especially the one-step oxidation and esterification of methacrolein to produce MMA,which has become a highly promising green and environmentally friendly process route.Nano Au catalyst is a reported catalyst that can efficiently achieve this green process route,but it also faces many challenges such as improving catalytic reaction activity and selectivity,cumbersome catalyst preparation steps,and easy deactivation of the catalyst.Therefore,exploring the preparation of highly active,selective,and stable nano Au catalysts for oxidative esterification has important theoretical significance and practical application value.Therefore,based on the existing work in the laboratory,this thesis aims to modulate the synergistic effect between Au and M_xO_y/Al₂O₃ carriers to improve the catalytic performance in the one-step oxidative esterification of methacrolein for the synthesis of MMA by modifying Al₂O₃ with a series of transition metal oxides and loading Au to produce Au/M_xO_y/Al₂O₃ catalysts.The catalytic performance of the catalysts in the one-step oxidative esterification of methacrolein for the synthesis of MMA was improved.And the correlation between the high activity of the catalysts and the structure and physicochemical properties of the carriers was corroborated with the help of XRD,SEM,TEM,H₂-TPR,NH₃-TPD,CO₂-TPD,FT-TR and other characterizations;At the same time,the influence of kettle reactor and fixed bed reactor on the catalytic performance of the prepared catalyst was explored,with the aim of exploring and optimizing nano gold catalysts with high catalytic activity,good selectivity,and strong stability,as well as controllable preparation methods.The results obtained are as follows:（1）Explored the characteristics of Al₂O₃ and the influence of doping agents on the reaction ability of Au/M_xO_y/Al₂O₃ catalysts.Research has shown that Al₂O₃,which has stronger Lewis acid sites,regular morphology and structure,uniform defect distribution,and small pore size,is suitable as a basic carrier;Composite carriers were prepared by modifying alumina with different transition metal oxides,and the transition metal oxide dopants were well dispersed on the surface of Al₂O₃.Among them,the nano gold catalysts supported by doping agents such as La and Zn exhibit good catalytic activity in the one-step oxidative esterification of MAL（Methacrylical）to MMA.This may be due to doping promoting the carrier to have more acid-base sites,promoting the catalyst’s adsorption and activation of reactants,thereby promoting the generation of intermediate products and subsequent MMA.（2）The effects of pre-treatment conditions of composite carriers and preparation methods of Au catalysts on the physicochemical properties,structure,and oxidative esterification to MMA reaction performance of Au/M_xO_y/Al₂O₃ catalysts were investigated,and optimized reaction conditions were obtained.A series of nano gold catalysts with excellent catalytic performance were prepared.The results indicate that the appropriate doping content and calcination temperature of the composite carrier are beneficial for improving the performance of the oxidative esterification reaction;The catalysts prepared by the co-precipitation method are more reactive,probably due to the more efficient introduction of the dopant,which produces more hydroxyl groups and moderate to strong Lewis acidic sites,enhancing the interaction with the carrier.And the larger specific surface area of the catalyst is favorable to promote the formation of smaller Au nanoparticles,which improves the reactivity of the nanogold catalyst.（3）Finally,the reaction stability of the prepared nano gold catalyst in equipment such as a reactor and a fixed bed was emphasized.The results show that the deactivation in the reactor is severe,which may be due to the loss of catalyst powder,but it is more likely that the water and reaction products generated during the reaction cover the surface of the catalyst,hindering the adsorption and activation of the active components on the reactants.In a fixed bed reactor,the prepared nano gold catalyst reacted continuously for 60 hours,and its catalytic activity remained basically unchanged,maintaining high catalytic performance,significantly superior to the cyclic reaction stability performance in the reactor.The electron microscopy results showed that the pre reaction nano Au particles were highly dispersed on the composite carrier;After a long reaction,only a small amount of nano Au particles appeared to agglomerate,and the catalyst slightly changed color,but most of the nano Au particles were still highly dispersed,which is consistent with the test results of good reaction stability in the fixed bed of the catalyst.