Preparation Of Modified Amorphous TiO₂-SiO₂ Catalyst And Its Application For Epoxidation Of Styrene

Epoxyethylbenzene is a kind of important product in fine chemistry,which can be used as ultraviolet absorbent,flavoring agent and diluent for epoxy resin.In addition,it is also used in organic synthesis and pharmaceutical and perfume industry et al.At present,the industrial production of epoxyethylbenzene is mainly from halogen alcohol method.However,the disadvantage of this method includes a high demand for equipment and serious pollution.Nowadays,it is a hot research topic for the direct epoxidation of styrene to styrene oxide,because it has the characteristics of mild operating conditions,environmental friendliness and so on.In this paper,TiO₂-SiO₂ was used as the catalyst and the support loaded with Pd,Ag,Co,Mo,W and other active components.The M/TiO₂-SiO₂ catalyst was prepared by the impregnation method?M denoted as the corresponding metal oxides?,and its catalytic performance in the epoxidation of styrene was systematically investigated.1.Preparation and characterization of TiO₂-Si02 and its catalytic performanceThe synthesis process of TiO_2SiO₂ was perfermed by the coprecipitation method,using sodium silicate as the silicon source,and taking a certain quality solution in water to get the solution A.At the same,titanium sulfate was selected as the titanium source and dissolved in water of 40? to obtain solution B.After that A and B were mixed and stirred for a certain time,with the pH adjusted to 9.5 by the sodium hydroxide aqueous solution.Then keep stirring for a certain period of time,after the process of static aging,filtering,washing,drying,and calcinations at 550? for 5 h,the titania-silica mixed oxides TiO₂-SiO₂ with different TiO₂ content of 35%,40%,45%and 50%can be successfully obtained.In this paper,XRD,FT-IR,UV-vis,SEM and TEM were used to characterize the TiO₂-SiO₂.The characterization results:XRD shows that the TiO₂-SiO₂ is amorphous in structure and has not formed rutile or anatase TiO₂ crystal in a certain range of TiO₂ content;FT-IR shows that the Ti-O-Si bond is formed in theTiO₂-SiO₂ system;SEM shows that the TiO₂-SiO₂ surface not porous;TEM shows that the different content of TiO₂ have different degrees of agglomeration of catalyst particles.In the hydrogen peroxide acetonitrile system,with TiO₂-SiO₂ as catalyst,the effects of catalyst TiO₂ content,reaction temperature,reaction time,different additives,the dosage of H2O₂,and the amount of catalyst for epoxidation reaction were studied.The results show that TiO₂-SiO₂ with the 40%TiO₂ content has the best effect on catalyzing styrene epoxidation.Under the opdimum conditions that styrene dosage is 1.56 g?15 mmol?,sodium hydroxide dosage is 0.1 g,the reaction time is 1h,reaction temperature is 60?,the amount of catalyst is 0.1 g and the molar ratio of 30%hydrogen peroxide and styrene is 5:1,the conversion rate and selective are 61%and 95.4%,respectively.2.Preparation and characterization of M/TiO₂-SiO₂ and its Catalytic PerformanceThe synthesis process of M/TiO₂-SiO₂:TiO₂-SiO₂ with the 40%TiO₂ mass fraction as the carrier,?NH4?10Wi2O4i,?NH4?6Mo7O₂4,Co?NO3?2,AgNO3 and PdCl2 as active components dissolve in water or hydrochloric acid prepared by the impregnation method.And then through drying,calcination,a series of loading or different calcination temperature of catalyst M/TiO₂-SiO₂ were prepared.The results show that:Pd/TiO₂-SiO₂>Ag/TiO₂-SiO₂>W/TiO₂-SiO₂,Mo/TiO₂-SiO₂>Co/TiO₂-SiO₂.Among them,the Pd/TiO₂-SiO₂ catalyst has the highest catalytic activity.At the same time,the amount of load has an effect on the catalytic activity,and the catalytic effect is the best of the load of 0.1%Pd/TiO₂-SiO₂.In this paper,XRD,UV-vis,FT-IR,SEM and TEM were used to characterize the M/TiO₂-SiO₂.The characterization results of the Pd/TiO₂-SiO₂ catalyst:XRD shows that the palladium is loaded on the catalyst with palladium oxide crystal load on the surface of the carrier.FT-IR shows that the palladium oxide has an effect on the carrier framework;SEM shows that the small grains loaded palladium oxide on the carrier's surface get more aggregated as the increasing of loading.TEM shows that the palladium oxide grains are uniformly dispersed on the surface of the catalyst,with the increasing of loading,palladium oxide particles have different degrees of reunion.In the hydrogen peroxide acetonitrile system,M/TiO₂-SiO₂ as catalyst,the effect of M content and calcination temperature on the oxidation reaction of styrene was investigated.The results showed that the best catalyst was Pd/TiO₂-SiO₂ among M/TiO₂-SiO₂,the loading was 0.1%,the calcination temperature was 450?,the styrene conversion was 67.9%,and the selectivity was 94.6%.