Preparation Of Rutile TiO₂ With High Specific Surface Area And Investigation On Its High Temperature Stability

As the most stable crystalline form of TiO₂,the rutile phase has been widely concerned because of its high refractive index,low thermal conductivity,and excellent catalytic performance.However,factors such as small specific surface area,easy sintering at high temperature,and complicated preparation process limit the practical application of rutile TiO₂.Therefore,exploring the low-temperature preparation method of rutile TiO₂ with high specific surface area and improving its high-temperature stability is the current research focus of rutile TiO₂.In this paper,low-temperature hydrothermal method and low-temperature uniform precipitation method are used to prepare nano-rutile TiO₂.Then high-temperature stability of nano-rutile TiO₂ could be improved by the modification via doping or compounding.Finally,a TiO₂-SiO₂ composite with high specific surface area and high stability is synthesized,and the application of TiO₂-SiO₂ composite material in the catalytic oxidation of HCl is investigated.Low-temperature hydrothermal method was used to synthesize Ce³⁺,Re⁷⁺,La³⁺,Zr⁴⁺and Co²⁺doped nano-TiO₂ powders.The results show that there is no regular change between the grain size of the doped samples and the metal ion radius,but the difference in morphology is obvious.When doped with Zr⁴⁺,the product has a mixed crystal structure of rutile and anatase with good dispersion of TiO₂ and a specific surface area up to 198.0 m²/g.High temperature calcination changed the crystal form of some samples,which reduced the specific surface area of the samples.La³⁺and Co²⁺promote high-temperature sintering of TiO₂ powder,while the doping of Ce³⁺and Re⁷⁺can suppress high-temperature sintering.TiO₂-SiO₂ composite nanoparticles with different TiO₂ content were synthesized by using low temperature homogeneous precipitation method and sol-gel method.It was found that the content of TiO₂ had little effect on the pore structure of TiO₂-SiO₂ composite,but it had a apparent effect on the specific surface area.The higher the TiO₂ content,the lower the specific surface area.Pure TiO₂ is easier to sinter at high temperature.The introduction of SiO₂provides a loadable surface for the sample,which improves the dispersion of TiO₂ and the stability of the TiO₂-SiO₂ composite.Regarding to the low temperature homogeneous precipitation method,the TiO₂ in the TiO₂-SiO₂ composite is an anatase phase when the concentration of TiOCl₂ is 0.1 M.With concentration of 0.3 M,it is a mixed phase of anatase and rutile.The rest of composites are rutile phase with higher TiO₂ content.For the sol-gel method,it is more beneficial to increase the specific surface area of the TiO₂-SiO₂ composite material.After high-temperature calcination,the value of the band gap of the sample decreases.When the calcination temperature is 500°C and the TiO₂ content is 40%,the band gap is largest with band gap energy of 3.0468 eV.Through the evaluation of RuO₂/TiO₂-SiO₂ catalyst,it can be seen that the TiO₂-SiO₂composite support will reduce the catalyst activity when TiO₂-SiO₂ supported RuO₂ catalyst was prepared by the sol-gel method,but the stability of the catalyst could improved to a certain extent.In contrast,using low temperature homogeneous precipitation method,the catalyst activity and stability of RuO₂ supported by TiO₂-SiO₂ composite are better than RuO₂/TiO₂ except the composite support prepared at concentration of 0.1M.The reason is that supports with high specific surface area can improve the high dispersion of RuO₂ and enhance the interaction between RuO₂ and TiO₂.