Synthesis Of TiO₂ Materials And Their Supported V₂O₅ Catalysts Applied To The Ammoxidation Of 3-Picoline

Nicotinic acid is an important organic intermediate, which is widely used in medicine, feedstuff additive, chemical reagent and additive and so on. At present, the supply of nicotinic acid is of shortage. Therefore, it is imperative to increase the production of nicotinic acid. The ammoxidation of 3-picoline can produce nicotinonitrile that is readily hydrolyzed into the desired product nicotinic acid. This process is most commonly used in the production of nicotinic acid, in which the ammoxidation of 3-picoline is a crucial step. The productivity of nicotinic acid based on the above-mentioned process is mainly dependent on the performance of a catalyst used in the ammoxidation of 3-picoline. Therefore, the development of such a catalyst with high activity and selectivity is of utmost importance.V₂O₅/TiO₂ catalysts have been considered to be effective in the ammoxidation of 3-picoline to nicotinonitrile. In the current study, different approaches in terms of catalyst preparation have been conducted. Porous TiO₂ materials are first synthesized and then they are used as supports to prepare V₂O₅/TiO₂ catalysts, which are used in the ammoxidation of 3-picoline. The different techniques such as XRD, N₂ adsorption, SEM, H2-TPR, Raman, etc., are used to characterize the synthesized TiO₂ and the prepared V₂O₅/TiO₂. The main results are summarized as follows:1. Using P123 as the template and the different concentrations of acetic acid (20%,40%, 80%) mesoporous TiO₂ supports, referred to as TiO₂-x where x represents theconcentration of the acetic acid used, were synthesized. The results show that the synthesized TiO₂ are nanoparticles and their BET specific surface area decreases first and then increase with increasing acid concentration. TiO₂-20 has the higest BET surface area among the synthesized samples. The TiO₂-X samples were used as supports to prepare 5 wt.% V₂O₅ loaded catalysts, referred to as V₂O₅/TiO₂-x, among which V₂O₅/TiO₂-80 shows the higest selectivity for nicotinonitrile due to its highly dispersed VO_x and oligomeric state of vanadium species on the support. The Ce-doped mesoporous TiO₂ (40% acetic acid used to prepare the mesoporous TiO₂) supports, referred to as Ce-TiO₂-y (y = 0.0, 0.05, and 0.1, respectively) where y represents the mole ratio of Ce to Ti, were prepared, and wheny = 0.1 a crystalline phase as CeO₂ appears in the support and the prepared catalyst V₂O₅/TiO₂ shows a lower activity in the ammoxidation. The V species were directly doped into the support TiO₂ to prepare the catalysts z wt.% V-TiO₂ where z represents the weight percent of V₂O₅ in the catalyst and is equal to 3.3 wt.%, 6.4 wt.%, and 12 wt.%, respectively), and these catalysts show higher BET surface areas as compared to those prepared by wet impregnation, and the catalyst 3.3 wt.% V-TiO₂ possesses the highest catalytic activity in the ammoxidation. Additionally, the mesoporous TiO₂ materials with irregular mesostructure were successfully synthesized using the mixture of P123 + CTAB or PEG + SDS as template, and these mesoporous materials remain stable in terms of structure after calcined at 300℃.2. The commercial TiO₂ (UV100, Merck, referred to as U and M, respectively, in abbreviation) samples were treated with 10 mol/L NaOH aqueous solution in a temperature range from 120℃to 180℃(T) for different times (t) and the resulting materials are referred to as U-T-t,M-T-t. The SEM characterization reveals that the materials prepared in a temparature range from 120℃to 150℃consist of nanotubes while the material synthesized at 180℃consists of nanorods. All the as-synthesized samples are hydrogen titanium hydrates (Na_nH_2-nTi₃O₇·mH₂O), and after calcined at 400℃the BET specific surface areas of the materials consisting of nanotubes are higher than 100 m²/g while the BET specific surface area of the material consisting of nanorods is lower than 50 m²/g. The 5 wt.% V₂O₅ loaded on U-120-24 catalyst, compared to those with the same amount of V₂O₅ loaded on U-T-t and UV100 supports, shows the best catalytic properties while 5 wt.% V₂O₅ loaded on M-T-tcatalysts do not show any catalytic activities.3. The Ti-embedded mesoporous SBA-15 materials with molar ratios of Ti to Si up to 4were successfully synthesized. The Ti/SBA-15 materials maintain the framework ofSBA-15 when Ti/Si＜1 while a rutile phase of TiO₂ appears when Ti/Si≥1.In summary, the catalysts of V₂O₅ supported on TiO₂ nanopaticles and nanotubes as well as on Ti/SBA-15 are not suitable for the ammoxidatin of 3-picoline on an industrial scale.