Preparation Of Au/TS-1 And Its Application In Gas-phase Propene Epoxidation

Propene oxide(PO)is an important bulk chemical and widely used in many areas of social life.The gas-phase epoxidation of propene with oxygen and hydrogen to synthesize PO has attracted the interest of many researchers because the reaction process is very simple(only one step)and environmental friendly(the only by-product is water)and no organic solvents are used.Until now,many gold catalytsts containing Ti sites such as Au/TiO2,Au/Ti-SiO2(mesoporous support)and Au/TS-1(microporous support)have been used to catalyze propene epoxidation with oxygen and hydrogen.Among these gold catalysts,Au/TS-1 displays the best catalytic activity and reaction stability and thus has promosing potential for industrial application.In this dissertation,we aimed at improving the catalytic performance of Au/TS-1 and reducing catalyst costs.The pretreatment conditions of Au/TS-1,the screening of alkaline promoters,the preparation of Au/TS-1 by the impregnation method were carried out,the research content and results are as follows:(1)The effects of pretreatment atmospheres and temperatures on the catalytic performance of Au/TS-1 prepared by the deposition-precipitation(DP)method were investigated.The research showed that the pretreatment of Au/TS-1 by the feed gases(C3H6,O2,H2 and Ar)was much better than that by single-component gas of O2,H2 and Ar.The temperature of 200? was the best pretreatment temperature.Further research revealed that H2-C3H6 was the important component of feed gases pretreatment to improve the performance of the catalyst.In a wide temperature range,the pretreatment of Au/TS-1 by H2-C3H6 dual-component gas not only activated gold species to form Au nanoparticles with moderate size,but also improved the hydrophobicity of the catalyst surface.The Au/TS-1 pretreated using H2-C3H6 at 300? achieved a propene conversion of 8.4%and PO selectivity of 81.3%at 200? and space velocity of 8000 mL gcat-1 h-1 in the epoxidation of propene.(2)Au/TS-1-XC catalysts(XC represents carbonate precipitants)modified by single-component alkali metal ion were prepared using the DP method.Na+ promoter was beneficial to increasing the propene conversion in the epoxidation of propene,Cs+ promoter was helpful in improving the PO selectivity.Au/TS-1 catalysts modified by dual-component Na+-Cs+were then prepared.Under the action of dual-component Na+-Cs+,the Au loading and surface acidity of the catalyst were modulately adjusted,and the absorption ability of propene on the catalyst was enhanced.Among these catalysts,Au/TS-1-NaC-CsC(10)catalyst without pretreatment achieved the propene conversion of 9.2%and PO selectivity of 91.2%in the epoxidation of propene.The performance of Au/TS-1-NaC-CsC(10)catalyst pretreated using H2-C3H6 at 300? could be further improved.(3)Au/TS-1-MDP catalysts were prepared by a multistep deposition-precipitation(MDP)method,the amount of gold could be significantly reduced compared to the DP method,which reduced catalyst costs.The 0.30Au/TS-1-MDP catalyst obtained by optimizing the preparation parameters achieved the propene conversion of 7.2%and PO selectivity of 85.5%in the epoxidation of propene,which was better than the performance of the catalyst prepared by the DP method(propene conversion of 6.4%and PO selectivity of 85.9%).(4)The impregnation method was used to prepare Au/TS-1-NaP catalysts(NaP represents Na3PO4)by using the Na3PO4 as the additive.It was found that a proper amount of Na3PO4 was beneficial to reducing the Au particle size,and moderately adjusting the acidity of the catalyst surface,and weakening the influence on the framework titanium species of the support,and thus the the performance of catalyst in the epoxidation of propene was enhanced.When Au/TS-1 was prepared using a proper amount of Na3PO4 and CsOH as the additive,the performance of Au/TS-1 was further improved.Among these catalysts,Au/TS-1-0.8NaP-CsH(1)catalyst achieved the propene conversion of 10.3%and PO selectivity of 89.0%.