Modification Of Au/TS-1 Catalyst For Direct Gas-Phase Epoxidation Of Propylene

Propylene oxide（PO）is a significant chemical intermediate,which can be used to produce polyether polyol,propylene glycol and other organic raw materials.In recent years,the process of the direct gas-phase epoxidation of propylene has the advantages of high economic benefits,environmental friendliness,simple operation,etc.,and is currently a research hotspot.However,there are still many problems in this reaction,such as easy deactivation of catalyst,low catalytic activity,and low H₂ efficiency.This article mainly focuses on the modification of titanium silicate zeolite（TS-1）and its propylene epoxidation performance.The work is as follows:First,Pd was introduced into the hydrothermal synthesis process,and the Pd-TS-1catalysts were successfully prepared.The epoxidation performance of the catalysts was investigated at different reaction temperatures,and the PO formation rate was the highest at190°C.At this temperature,Pd-TS-1-1.25 had the best catalytic performance,and the PO formation rate was～205 g _POh^-1kg_cat^-1,which was much higher than that of Au/TS-1.The ICP results showed that an appropriate amount of Pd was beneficial to increase the Ti content and Au loading of the catalyst.The results showed that PO formation rate was the highest when Pd/Ti ratio was 0.019 and Pd/Au ratio was 0.276.The results of O₂-TPD,DRIFTS,etc.indicated that the introduction of Pd improved the oxygen adsorbing capacity of the catalysts to a certain extent,which was conducive to the formation of more H₂O₂,thereby increasing PO formation rate.Secondly,in order to solve the problem that the carbon deposits which was generated in the reaction was easy to block the microporous channel causing the catalyst deactivation,the TS-1 sample was post-treated with TPAOH solution,and the H-TS-1 was successfully synthesized.Au/H-TS-1 showed good stability,and the PO formation rate only decreased by10.3%for 100 h,while that of Au/TS-1 catalyst decreased by～28.3%.The results of TG and FTIR indicated that the weight of carbon deposits of Au/H-TS-1,which was only～3.56 wt%,was less than that of Au/TS-1 at 200°C for 50 h.The hollow structure improved the diffusion capability of the catalyst,which could reduce the formation of carbon deposits and improve the stability of Au/H-TS-1 in propylene epoxidation reaction.Finally,TS-1-x was prepared by one-step hydrothermal synthesis method using（NH₄）₂SO₄as the crystallization regulator.The results showed that adding proper amount of（NH₄）₂SO₄into the precursor solution could reduce the generation of Ti species outside the framework and increase the Ti content of the zeolite（from 0.803 wt%to 1.087 wt%）,and the introduction of NH₄⁺changed the charge state of the catalyst surface,which was beneficial to increase the Au loading（from 0.0278 wt%to 0.0802 wt%）.However,the particle size increased（>0.45μm）,and large Au nanoparticles were easily formed,which influenced the PO formation rate.