Amorphous Catalyst Synthesis And Its Effect On Epoxidation Of Propylene By CHP

In this thesis,Pd/Ti-MCM-41silylated mesoporous molecular sieves were synthesized using hydrothermal crystallization method,then its catalytic activity on propylene epoxidation were investigated.At the same time,Pd/TiO2-SiO2 composite oxideswere prepared by coprecipitation,also its catalytic activity on propylene epoxidation were investigated.1.Pd/Ti-MCM-41 silylated catalyst(PdTM-ZS)This thesis prepared the silylated Pd/Ti-MCM-41(PdTM-ZS)catalysts prepared by treating the series Ti-MCM-41 samples(Si/Ti molar ratio = 10,15,20,25 and 30)with palladium loading followed by surface silylation with trimethylchlorosilane.The structure and the form of titanium were characterized by means of XRD,UV-Vis,FT-IR,TEM,SEM,XPS and N2 adsorption.This thesis investigated the effects of Si/Ti molar ratios on the structure of molecular sieves.The research result showed that molecular sieves with mesoporous structure have been successfully synthesized.The lowering in the structure regularity due to the incorporation of Ti into the framework and the optimum Si/Ti molar ratio was 20.Among the series PdTM-ZS catalysts,the PdTM-20S catalyst has the most titanium active sites.Reaction results show that the PdTM-ZS catalysts can be applied as efficient catalysts for the selective production of propylene oxide from the oxidation of propylene with cumene hydroperoxide as the oxidant.Among the series PdTM-ZS catalysts,the PdTM-20S catalyst exhibits the best catalytic performance with the selectivity of propylene oxide approaching 99%and the conversion of propylene keeping 62.5%.The experimental result indicated that the modification with trimethyl chlorosilane also results in improving the stability and reaction selectivity.Excessive reaction temperature accelerates the decomposition of CHP and the low flow rate of propylene is not conducive to the formation of PO.The experimental result indicated that optimum reaction conditions were:the amount of trimethylchlorosilane was 40 wt%;the reaction temperature was 80 °C;when the CHP feed rate is 0.18mol/h,the propylene flow rate is about 0.45mol/h,and the feed molar ratio of propylene to CHP is 2.5.Under the optimum synthesis conditions,the PdTM-20S catalyst shows the optimal reaction performance with propylene conversion of 62.5%and PO selectivity of approximate 98%within 30 hours.2.Pd/Tio2-SiO2 silylated catalystThe synthesis process of Pd/Tio2-SiO2:PdC12 as active components dissolve in hydrochloric acid prepared by impregnation loading method.And then through drying,roasting,prepared a series of different calcination temperature of catalyst Pd/TiO2-SiO2.The structure and the form of titanium were characterized by means of XRD,UV-Vis,FT-IR and TEM.This study investigated the effects of calcination temperature on the structure of molecular sieves.The research result showed that the optimum calcination temperature was 500°C.The experimental result indicated that the modification with trimethyl chlorosilane also results in improving the stability and reaction selectivity.Excessive reaction temperature accelerates the decomposition of CHP and the low flow rate of propylene is not conducive to the formation of PO.The experimental result indicated that optimum reaction conditions were:the amount of trimethylchlorosilane was 4 wt%;the reaction temperature was 100°C;when the CHP feed rate is O.15mol/h,the propylene flow rate is about 0.375mol/h,and the feed molar ratio of propylene to CHP is 2.2.Under the optimum synthesis conditions,the Pd/TiO2-SiO2 silylated catalyst shows the optimal reaction performance with propylene conversion of 8.4%and PO selectivity of approximate 95%within 3 hours.The observed excellent performance of PdTM-ZS catalysts can be attributed to the effects regarding abundant active sites,rules channel and appropriate pore size.The silylated PdTM-ZS catalysts also has a great potential to be extended to other catalytic oxidation reactions and beyond.Although the catalytic effect of Pd/TiO2-SiO2 silylated catalyst composite oxide catalyst is not as good as PdTM-ZS,the preparation method of Pd/TiO2-SiO2 silylated catalyst is simple.Because the preparation of Pd/TiO2-SiO2 silylated catalyst process does not use the template agent to avoid the collapse of the tunnel and environmental pollution problems caused by the molecular sieve in the high temperature,but also has the space of development and utilization.