Catalytic Performance Regulation Of Au/TS-1 For Direct Gas-phase Epoxidation Of Propylene

Propylene oxide（PO）is the third most significant propylene derivative,following polypropylene and acrylonitrile,and is extensively applied in the light,medical,and textile industries.The recently developed hydrogen peroxide technology for PO preparation is gradually replacing traditional chlorohydrination and co-oxidation methods due to its eco-friendliness and ease of operation.However,there are still problems such as H₂O₂storage security and separation of reaction products from solvents.The direct oxidation of propene using oxygen for PO production in the presence of hydrogen further improves the hydrogen peroxide oxidation method.Expected to become the mainstream PO production process in the future.However,the conversion,selectivity,and stability of Au/TS-1 catalysts commonly used in this technique during the reaction are still not ideal,and there is an urgent need for research on catalyst composition structure regulation and packing technique to refine the related theoretical basis and better meet practical demands.This study investigated the micro/nanostructure and reaction performance differences of catalysts prepared by sol immobilization and deposition precipitation methods,regulating Au deposition location and particle size distribution in the support,etc.,to optimize the prepared SI-Au/TS-1-B catalyst and DP-Au/TS-1 catalysts,respectively.The influence of Au loading,Si/Ti of supports,and atmosphere treatment on the reaction performance was investigated,and the catalyst deactivation and regeneration mechanisms were analyzed.Based on the comparative results,the deposition precipitation method combined with catalyst forming technique was selected to prepare the catalytic material of a membrane tube with a microchannel structure,and the reaction efficacy study was carried out.The specific research content is as follows:The SI-Au/TS-1-B catalysts were synthesized by the sol immobilization method using uncalcined TS-1（TS-1-B）as the support.The abundant template agent tetrapropylammonium ion（TPA⁺）inside TS-1-B would block the micropores,thus preventing Au loading inside the molecular sieves,avoiding fast deactivation during the reaction.TS-1-B,on the other hand,being nearly electronegative to the Au sol,significantly increases the Au capture rate（more than 99%）.Examination of the effects of Au loading and hydrogen pretreatment revealed that the Au（0.1）/TS-1-B catalyst after hydrogen thermal treatment exhibited enhanced PO selectivity,a shortened induction period,and a slowed deactivation rate.Characterization analysis revealed that moderate decomposition of organic components,decreased acidity,and increased hydrophobicity on the surface of the catalyst were the main reasons.At an optimized gold loading of 0.1 wt%,the PO selectivity was78.2%,and the average PO generation rate was 80.6 g PO·h^-1·kg cat^-1.The DP-Au/TS-1 catalysts were prepared using TS-1 with template removal by calcination as a support.Au was loaded on the surface of the support and inside the pore channels using cesium carbonate as a precipitant.Comparing the SI-Au/TS-1-B catalysts,the replacement of TS-1-B by TS-1 decreased the noble metal capture rate during the Au loading in the DP method.However,the interaction of Au and TS-1 internal pore channels significantly increased the PO production rate.Factors such as the Au loading and the Si/Ti of TS-1 were examined for their influence on the reaction performance,and the optimal Au loading was obtained as 0.8 wt%with a Si/Ti of 100.At a reaction temperature of 240°C,the Au（0.8）/TS-1（100）catalyst exhibited an average PO production rate of 171.3 g PO·h^-1·kg cat^-1and a PO selectivity of 75.4%.Analysis of the catalyst deactivation process and regeneration methods revealed that the critical factor was the rapid blockage of molecular sieve channels during the pre-reaction period.Applying H₂/O₂mixed gas treatment could quickly restore catalyst activity and improve catalyst stability.Based on the needs of the above catalyst contrasts and the demands of filling applications,materials such as 3D printed materials and Al₂O₃hollow fiber tubes were used as supports for the surface growth of the TS-1 membrane layer.In turn,the DP method was selected to load Au for structural characterization and reaction tests.It has been found that an Al₂O₃hollow fiber tube surface modification by coupling agent and then coated with TS-1 seeds can prepare more continuous membrane layers,in which TS-1 crystals grow inside the pore channels,forming a microporous channel reactor structure.The prepared material exhibits the advantages of high TS-1 growth（5.93 wt%）and low mass transfer resistance（pressure difference<0.02 MPa inside and outside the tube）.Compared with the powdered catalyst,the catalyst from this composite membrane showed a much more single predominantly propane,with Po selectivity of 71.3%.The average PO production rate could reach 77.84 g PO·h^-1·kg cat^-1.This class of catalytic materials is expected to improve performance by forming monoliths,being easy to fill,convenient to regenerate,and having high application prospects after subsequent optimization of preparation conditions and reaction environment.