The Construction And Catalytic Properties Of Supported Ag/Cu Bimetallic Catalyst

Noble metal nanoparticles have become indispensable catalyst materials because of their excellent catalytic performance.However,noble metals limit their further application because of their high price and rarity.Therefore,the use of abundant and cheap base metals to replace noble metals has become a new research direction.However,further studies have shown that the catalytic activity of base metals is significantly lower than that of noble metals,leading to their limited application.The construction of bimetallic catalysts combined with noble metals and base metals can not only effectively reduce the cost of preparation of the catalysts,but also result in higher catalytic activity,selectivity and stability than that of single metals due to the synergistic effect of the bimetallic catalysts.However,the composition and structure of bimetallic catalysts are dominated by bimetallic nanoparticles or surface-supported bimetallic catalysts,which lead to their lower surface area and the disadvantages of easy aggregation.In this paper,hollow/porous silica（Si O₂）based bimetallic catalysts were prepared by using silver and copper nanoparticles as catalytic active centers and using high specific surface area as support.The influence of catalysts on hydrogenation of nitroaromatic hydrocarbons was studied by adjusting the composition,structure and proportion of bimetallic particles.The main research contents are as follows:（1）In order to solve the problems of easy aggregation and poor dispersion of metal nanoparticles,single layer hollow/porous silica（HS）was selected as the carrier and silver or copper nanoparticles were used as catalytic active centers to prepare hollow Si O₂-supported silver catalysts（HS-Ag）and copper catalysts（HS-Cu）.Since Si O₂ has good hydrophilicity,chemical inert and hollow/porous structure,it is not only beneficial to inhibit the aggregation of metal nanoparticles,but also can effectively reduce the diffusion limit of reactants and products,leading to good hydrogenation behavior of nitroaromatic hydrocarbons in the synthesized catalyst.The results showed that at 25℃for 150 min,in the presence of HS-Ag the conversion nitrobenzene（NB）and p-nitrophenol（4-NP）reached 91.6%and 78%,respectively,while the HS-Cu catalyst also achieved 91.1%（NB）and 42%（4-NP）under the same conditions.（2）In order to solve the problem of poor catalytic performance of base metals,HS-Ag/Cu bimetallic catalysts（HS-Ag/Cu）were prepared by using hollow/porous Si O₂ as support and silver and copper as bimetallic catalysts.Due to the synergistic effect of silver and copper,the synthesized catalyst has better hydrogenated nitroaromatic behavior than that of single metals（HS-Ag and HS-Cu）.Hydrogenation experiments of nitroaromatic hydrocarbons show that:After 150 min of reaction,in the presence of HS-Ag/Cu the conversion of 4-NP was nearly 96.3%,which was higher than that of HS-Ag（78%）and HS-Cu（42%）under the same conditions,indicating that the catalytic performance of copper nanoparticles in HS-Ag/Cu catalyst reached or was higher than that of noble metal silver catalyst.In addition,the synthesized HS-Ag/Cu catalyst also obtained good cycling stability.（3）In order to solve the problem of poor cyclic stability of surface-supported metal particles,the Ag/Cu confined catalyst（Si O₂-Ag/Cu@Si O₂）was prepared using fractional hollow silica as the confining carrier and silver/copper bimetallic as the catalytic activity center.The synthesized Si O₂-Ag/Cu@Si O₂ catalyst is confined between inner and outer Si O₂,which effectively prevents the metal nanoparticles from falling off and aggregating during the catalytic process,resulting in higher catalytic activity and stability.At 25℃,NB in the catalyst catalyzed,reaction time reached 60minutes,under the Si O₂-Ag₁/Cu₂@Si O₂ catalyzed conversion rate is 89.62%,under the Si O₂-Ag₂/Cu₁@Si O₂ catalyst conversion rate has reached 99.85%,the substrate reaction is almost completed.It was higher than the surface supported HS-Ag/Cu catalyst（73.4%）under the same reaction conditions.Cyclic experiments also showed that the conversion rate of p-nitrobenzene was still up to 86.2%after four cycles of confined Si O₂-Ag₂/Cu₁@Si O₂ catalyst.