Preparation Of Organically Modified SiO₂ Supported Cu-based Catalyst And Study On The Reaction Performance Of Methanol Synthesis

Cu-based catalysts have been widely used in a series of industrially important reactions,including synthesis of alcohols from syngas,dehydrogenation of alcohols,steam reforming of methanol,water-gas shift reaction,oxidation of CO and hydrocarbons and selective hydrogenation of carbonyl compounds because of their high activity.Especially,the production of methanol from syngas or CO₂over Cu-based catalysts has been studied extensively from theory to industrial application.Compared to methanol synthesis via syngas,the formation of water vapor is inevitable in direct CO₂ hydrogenation to methanol,which leads to serious catalyst deactivation.It is found that the accelerated growth of Cu particles by the presence of water vapor byproduct,is the main reason for deactivation during the reaction process.Several studies had shown that the water has an obvious influence on the physical structure,electronic properties and catalytic process of Cu-based catalysts.It was also found that the water molecules easily adsorbed on Cu surface,resulting in the increase of oxidized copper species,which would be directly related to the catalytic activity.As a result,the water byproduct easily induced the copper particle growth by particle migration and aggregation or Ostwald ripening,leading to active metal surface reduce,which would cause catalyst rapid deactivation.The poor stability of Cu-based catalysts during the reaction in the presence of water byproduct is the bottleneck for further industrial application.Due to the adverse effects of water on copper-based catalysts,we designed a series of organic modified SiO₂ supported copper based catalysts and investigated their methanol synthesis reaction performance in detail.The main conclusions of this paper are as follows:?1?Methyl-modified silica supported Cu-based catalysts were prepared.In order to examine the effect of water on the catalyst,a large amount of water?0.6mL/h?was added during the reaction.From the results of the catalytic reaction evaluation,it was found that the non-methyl modified CuZn and Cu Zn/SiO₂catalysts rapidly deactivated after the addition of water,while the catalysts modified by different amounts of methyl had a significant reduction in the deactivation rate.XRD,TEM and XPS et al.characterization showed that under the action of water,the agglomeration and growth of active metal Cu and the oxidation of metal copper to divalent copper were the main reasons for the catalyst deactivation.Compared to the non-methyl modified catalysts,the growth and oxidation degree of metal copper particles of methyl modified copper-based catalysts in the induction of water greatly reduced,which was due that the surface methyl group effectively inhibited the adsorption of water molecules on the active center,thereby retarding the agglomeration and growth of the active component particles and thus improving the stability.?2?Different organic groups?Methyl,Ethyl,Propyl?modified silica supported copper based catalysts were prepared.To examine the effect of different groups on the stability of the catalyst during the reaction under water conditions,a certain amount of water was added?volume fraction 1.5%?.The catalyst reaction evaluation results displayed that the non-group modified CuZn and CuZn/SiO₂catalysts rapidly deactivated after adding water,whereas for different group modified catalysts,the deactivation rate decreases significantly with the enhanced hydrophobicity of the modified group,and the order of the catalyst stability was Cu Zn/SiO₂-M<CuZn/SiO₂-E<CuZn/SiO₂-P.XRD,TEM,XPS et al.characterization results proved that the main reason of the catalyst deactivation was the agglomeration and growth of active center metal copper under the induction of water.Different from the catalysts in the case of large amounts of water?0.6 mL/h?,the active sites of the catalyst were not oxidized to divalent copper but oxidized to monovalent copper.Compared to unmodified catalysts,the degree of agglomeration and growth of different groups modified catalysts induced by water greatly reduced,particularly propyl modified catalysts,which may be due to the hydrophobic effect of the groups,and more importantly,the physical barrier of the molecular chain of the group,thus significantly improving the stability of the catalysts.