Bio-template Synthesis Of TiO₂ And Its Catalytic Performence Of Selective Hydrogenation

TiO2 has been widely used in the fields of information,medical treatment,materials,environment,energy and catalysis,as a transition-metal semiconductor material.Many reports show that the morphology and structure of TiO2 is closely related to its application performance.In general,the morphology of TiO2 prepared by chemical method is single,and the preparation process is mostly tedious.It is significant to seek a green and convenient method to obtain TiO2 with special morphology and structure.In addition,there are many special structures in nature.The bio-template method is to use the biomass with special structures as template to obtain the material which own special structure.In this paper,TiO2 with different morphology was prepared by bio-template method.Then the supported Pd/TiO2 catalysts were obtained by sol immobilization method(SI),and were applied in selective hydrogenation of 1,3-butadiene to explore the relationship between material structure and catalytic performance.A facile method was employed to prepare TiO2 hollow fiber materials(Cotton-TiO2)by using defatted cotton fibers as the template.The concentration of precursor and the soaking time of cotton fiber had an important effect on the structural replicated,Cotton-TiO2 with good hollow tubular structure could be prepared when TBOT/EtOH volume ratio was 4:150,soaking time was 48 h.SEM,XRD,BET and other characterizations showed that Cotton-TiO2 obtained in different calcination temperature was anatase with 1-D hollow tubular structure.With the increase of calcination temperature,the specific surface area of Cotton-TiO2 increased first and then decreased.Furthermore the supported Pd/Cotton-TiO2 catalysts were obtained via sol immobilization method,characterizations such as TEM and XPS showed that Pd nanoparticle size was about 7.1 nm,which existed in the state of zero and two valence.The effect of calcination temperature on the catalyst performance was investigated.It was found that the calcination temperature had little effect on the catalytic performance,and the Pd/Cotton-TiO2-550(calcination temperature was 550 ?)had better catalytic performance,with the conversion rate of 88.23%,the butene selectivity of 94.5%and the 1-butene selectivity of nearly 60%.The cotton template had a great influence on the properties of the support and the performance of the catalyst.Compared with the TiO2 prepared without the cotton template,the morphology and structure of TiO2 shifted from spherical particles to the 1-D hollow tubular structure,the specific surface area of Cotton-TiO2 increased 100%.Moreover the catalytic performance of the Pd/Cotton-TiO2 was greatly enhanced,especially the 1-butene selectivity was improved by nearly 46%.Longan leave was also chosen as the bio-template to prepare porous TiO2(Leaf-TiO2).The obtained structure was dependent on the concentration of precursor and the soaking time of Longan leave,and Leaf-TiO2 with good porous structure was prepared when leave was soaked in 5 wt%TiCl3/EtOH solution of 24 h after acid-base pretreatment.In the aid of TG and FTIR characterization,the replication process can be described that:(?)the Ti precursor interact with the active group of leaf accompanied by ion exchange or chelation;(?)The amorphous TiOx are obtained in hydrolysis/alcoholysis;Finally the Leaf-TiO2 maintained the porous structure is formed after calcination removing the biotemplate.SEM,XRD,BET and other characterizations showed that Leaf-TiO2 was anatase with porous structure,the specific surface area of Leaf-TiO2 is nearly three times higher than that of Cotton-TiO2.Then the supported Pd/Leaf-TiO2 catalysts were obtained by sol immobilization method,characterizations such as TEM and XPS indicated that Pd nanoparticle was about 7.2 nm,which existed in the state of zero and two valence.When the Pd/Leaf-TiO2 catalyst was applied to the selective hydrogenation of 1,3-butadiene,the results showed that the performance of porous Pd/Leaf-TiO2 was higher than that of hollow tubular structural Pd/Cotton-TiO2,with the 1,3-butadiene conversion and 1-butene yield increased by 5%and 4%respectively.