Structural Characteristics And Acidity Of Titanate Nanomaterials

Catalysts have been playing an important role in the modern chemical production process,among which acidity is an extremely important property of catalysts.The relationship between structural characteristics and acidity of catalysts and the improvement of acidity characteristics of catalysts have been widely paid attention to by researchers.In this paper,layered Na2Ti3O7 was prepared by high-temperature solid phase method,and the layered H2Ti3O7 was prepared by acidification.H2Ti3O7 nanosheet was prepared by using methylamine and propylamine to exfoliating the layered H2Ti3O7.The H2Ti3O7 nanotube was synthesized by the hydrothermal method.The physical and chemical properties of catalysts were studied by X-ray powder diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),thermogravimetric(TG),N2 adsorption-desorption,laser Raman spectroscopy(LRS)and Pyridine-adsorbed FT-IR(Py-FTIR).The esterification reaction between acetic acid and n-butanol was used as probe test to verify and explain the characterization results.Studies have found that layered H2Ti3O7 has the lowest catalytic performance,and the catalytic performance of the H2Ti3O7 nanosheet is improved.This is due to the greatly increased specific surface area of the H2Ti3O7 nanosheet after exfoliation,reaching 114.9 m2·g-1.At the same time,there were not only L acid sites exists on the surface of the nanosheet,but also a lower concentration of B acid sites.Although nanotube has a similar crystal structure to nanosheet,its specific surface area is much larger than that of nanosheet,reaching 365.9 m2·g-1.On the one hand,titanate nanotube has higher concentrations of B acid sites.On the other hand,due to the bending of TiO6 octahedral layers during the synthesis process,the acid strength of bridging hydroxyl of nanotube is stronger than that of nanosheet.In addition,the unique one-dimensional tubular structure of titanate nanotube can provide additional places for chemical reactions,and there may be a confinement effect to promote the esterification reaction.Therefore,when nanotube is used as catalyst,the catalytic activity is the highest.The prepared nanotube was doped with Zn and Zr ions,and sulfate radicals were loaded.At the same time,the in-situ hydrothermal method was used to dope Nb during the nanotube forming process.The above three methods were used to improve the acidity of titanate nanotube.The physical and chemical properties of catalysts were measured by X-ray powder diffraction(XRD),scanning electron microscopy(SEM),energy spectrum analysis(EDS),Fourier transform infrared spectroscopy(FT-IR),laser Raman spectroscopy(LRS)and solid state nuclear magnetism(1H MAS NMR).The reaction of acetic acid and n-butanol was still used as a verification experiment.Studies have found that the increase of acidity of titanate nanotube doped with Zn and Zr ions by ion exchange is relatively weak.After larger cations are inserted into the nanotube layers,the bending degree of bridging hydroxyl Ti-O(H)-Ti bond may be weakly enhanced,thus improving the acidity of the nanotubes.Although sulfate-supported nanotube has high catalytic activity,there are a series of defects.However,the in-situ doping method is relatively stable,and the Raman redshift phenomenon is more obvious than that of ion exchange method,which further enhances the lattice distortion of nanotube.In addition,a new bridge hydroxyl Ti-O(H)-Nb bond may be formed in the process of in-situ Nb doping,which can improve the acidity of the titanate nanotube.Figure[22]table[6]reference[83]...