Study On Modification And Forming Of V₂O₅/TiO₂ Catalysts For Synthesis Of Nicotinic Acid By One-step Method

As an important chemical and pharmaceutical intermediate,Nicotinic acid was usually synthesized by some traditional methods,such as electrochemical oxidation,liquid-phase oxidation and ammoxidation,The disadvantages of above processes include serious pollution,low productivity and complexity of process steps.One-step oxidation synthesis of nicotinic acid with air which used 3-picoline as a raw material and air as an oxidant,the advantages is environment-friendly,low cost and high quality products,reveals a promised prospect for application in indusry.The key technique of the reaction is catalysts,V2O5/TiO2 catalysts were studied in the paper,By doping additives and modifying surface area spport,catalytic activity of the catalysts were improved.And the preparation of the catalysts were also investigated in this paper.The conclusions were listed as follows:A series of V2O5/TiO2 catalysts doped with different chromium content,which is prepared by impregnation with the carrier anatase TiO2 made prepared by co-precipitation,and characterized by XRD,BET,H2-TPR,NH3-TPD.The results showed that a new crystalline phase CrV04 appeared on the Cr-doped catalysts,which could reduce the crystal size of V2O5 and TiO2,and increase the acidity of catalysts.A small amount of Cr doping would promote the mobility of the lattice oxygen of V2O5,and improved the yield and selectivity for nicotinic acid.But excessive Cr doping would increase the number of surface oxygen,and lead to a decline in selectivity of nicotinic acid.Selectivity of Nicotinic acid could reached 90%on V2O5/TiO2 with 2wt%Cr at 260?.In order to impove the catalytic activity and stability of the catalysts in reaction at wide experimental temperature.The influence of the Ti02 spports with different surface area on catalytic activity were investigated,the results showed that the catalytic activity increased with the surface area of TiO2.The active phase of V2O5 will reach at monolayer-dispersion when Ti02 surface area was 120 m/g.With the Ti02 surface area of 200 m2/g,the selectivity of Nicotinic acid could reached 97%at 260? on Cr0.02V0.98O2.48/TiO2(200)catalyst,and also maintainde good activity and selectivity in the range of 250-280?.The XPS characterization of catalyst showed that the quantivalency of V changed from +5 to +4 and the catalytic activity maintained stable when V5+/V4+=0.19.The preparation methods of monolithic V2O5/TiO2 catalysts were also studied in the paper.The effect of mechanical strength with different methods and different additives for the monolithic V2O5/Ti02 catalysts were studied.The results showed that mechanical strength of the monolithic catalysts were in the follow:Al2O3 + ethanolamine>PEG2000+ ethanolamine>ethanolamine.And PEG2000+ethanolamine additives could not only ensure the mechanical strength,but also maintain the original catalytic activity.The effects of reaction temperature,space velocity,oxygen partial pressure and other conditions on catalytic activity were also investigated.It was showed that prepatation process of the monolithic catalysts played little effect on the original activity.