Establishment And Acidic Research Of Nb-based Composite Oxide Nanotubes

N-butyl acetate is not only an important organic compound,but also is an important fine chemical.The esterification of acetic acid with n-butanol is a main route of preparing n-butyl acetate.However the route needs sulfuric acid as catalyst.Although the route has higher esterification rate,there are many shortcomings such as difficult separation of products,corrosion of equipment,serious pollution and so on.Solid acid can overcome those shortcomings and own many excellent performances such as surface strongly acidic,highly selectivity and non-pollution.Thus,solid acid as acid catalyst has been widely studied and great potential for development.In this research,K4Nb6O17 was prepared by a high temperature solid state reaction method.Then K4Nb6O17 were modified by proton-exchange,exfoliation,sol-sol composite method,acid precipitate,calcinations,dipping of sulfuric acid,and Nb-based composite solid acid materials were obtained.The properties of samples were characterized by XRD,HRTEM,N2 adsorption-desorption,Raman,FT-IR,NH3-TPD.The catalytic activities of samples for esterification of acetic acid with n-butanol have been investigated,and SO42--ZrO2@NT-Nb2O5(1:3,0.5)composites own the highest acid catalytic activity.Nanotubes NT-H4Nb6O17 was formed by scrolling laminate itself,which own bigger specific surface area(182 m2·g-1)and pore volume(0.46 cm3·g-1)3 and the diameter of the nanotubes is uniform and tube length is longer.NT-H4Nb6O17 was soaked in sulfuric acid solution and its specific surface area,acid strength and acid quantity all increased.In addition,the sulfuric acid concentration increases,the increase is more obvious.The morphology of composite materials depends on their content of Zr element and Nb element.When the molar ratio of Zr to Nb is 1:3,composite materials presented nanotube structures.When the ratio is 1:2,composite materials own nanosheet structures.ZrO2 oxide nanoparticles are dispersed on the surfaces of laminate and changed the tension on the surface of laminate.So when the composite ratio increases,the laminate can not scroll to form nanotube structure.Compared with NT-H4Nb6O17 materials,the specific surface area and pore volume of composite materials all decreased.The soaking of sulfuric acid made composite materals' specific surface area,acid strength and acid quantity increased.Furthermore,the sulfuric acid concentration increases,the increase is more obvious.The esterification of acetic acid with n-butanol was employed to evaluate the acid catalytic performance of samples under fixed esterification reaction conditions.And the results shown that SO42--ZrO2@NT-Nb2O,(1:3,0.5)composites own the excellentest acid catalytic performance.The four factors of molar radio of n-butanol and acetic acid,the reaction temperature,the reaction time and the amount of catalyst were chosen as the test index.At the same time orthogonal experiments were designed with each factor three levels to test the catalytic activity of SO42--ZrO2@NT-Nb2O5(1:3,0.5)composites for the esterification of acetic acid with n-butanol.The experimental results showed that:the yield of the reaction reached up to 90.3%under the optimization schemes due to its nanotube structure,higher amount of acid and stronger acidity.And taking single-factor optimization test to gain the optimum reaction conditions for SO42--ZrO2@NT,Nb2O5(1:3,0.5)composites.