Preparation And Characterization Of Copper-based Bimetallic Catalysts And Their Applications In The Gas-phase Selective Oxidation Of Alcohols

In the field of organic synthesis,the selective oxidation of alcohols to the corresponding carbonyl compounds is one of the most important chemical reactions.Aldehydes and ketones are widely used as solvents,polymer precursors,high-value added components in perfumes and intermediates of dyes and drags.The traditional preparation methods of aldehydes and ketones need to add a large number of expensive and toxic chromate or permanganate oxidation agent,resulting in great pollution and waste.The concept of "green chemistry" requires us to realize the production of atomic economy and environmental protection.Therefore,a lot of research work has been carried out in the field of heterogeneous catalytic oxidation of alcohols by using green oxygen or hydrogen peroxide as oxidant in recent years.The selective gas-phase oxidation of alcohols adopts oxygen as oxidant to solve the separation problem of products and catalysts,and it can achieve continuous production without solvent.Supported metal catalysts such as gold,palladium,silver and copper have been extensively researched in the gas-phase oxidation of alcohols.Copper-based catalysts with advantages of low cost and simple preparation exhibit very high catalytic activity,which have broader prospects for industrial applications.Small particle size is required to reach high catalytic activity because of the simple structure of single metal catalyst.Bimetallic catalysts can not only break through the"size effect" of the single metal catalyst,but also have "synergistic effect" between the two components,making them more potential in modem chemical industry.Based on the above analysis,the molecular oxygen is adopted as oxidant and supported bimetallic catalysts are used to study the system of gas-phase catalytic oxidation of alcohols in this paper.1.Copper-based bimetallic catalysts for gas-phase oxidation of benzyl alcoholAuCu bimetallic catalysts supported on SBA-15 and SiC were prepared respectively.Three aspects of these catalysts including catalytic activity,lifetime and thermal stability were compared,with the result of high thermal conductivity SiC being preferred as catalysts support.Then the optimal preparation conditions were determined:calcination at 300? for 2 h followed by pre-activation at 380? for 0.5 h.With the comparison of activity on different catalysts,conclusions were obtained as follow:1.Bimetallic catalysts were better than monometallic catalysts;2.Copper-based bimetallic catalysts were better than other bimetallic catalysts;3.AgCu/SiC performed the highest catalytic activity with 99.3%conversion and 99.6%selectivity.AuCu/SBA-15 has poor active CuO sites while SiC supported copper-based catalysts with high-performance all have active Cu₂O sites.It is noteworthy that AgCu/SiC is more conducive to industrial applications due to low cost and high activity.2.The outstanding low-temperature catalytic activity over AgCu/SiC for gas-phase oxidation of alcoholsPre-activated Ag2.5CU5/SiC catalyst performed excellent catalytic activity,for example,the conversion and selectivity could correspondingly reach 99.3%and 99.6%as well as lifetime of 215 h with O₂/hydroxyl = 0.6 and WHSV = 10 h-1 at 280?.Compared with the reported catalysts,Ag_2.5Cu₅/SiC still exhibits very remarkable performance.The formation of Ag-Cu₂O ensembles brought about enhanced improvement both in conversion and stability.The Characterization results revealed that large amounts of Ag0-Cu₂O active sites were formed after pre-activation process and Cu₂O sites played a dominant role in benzyl alcohol oxidation reaction.The role of Ag is mainly reflected in the formation of the Ag-Cu₂O ensembles to enhance the stability of the catalyst.Dehydrogenation reaction process has also been confirmed by O₂-TPD.As an oxidant,O₂ plays an indispensable role in the oxidation of alcohols,which further confirms the catalytic dehydrogenation mechanism.