Deactivation and oxidative regeneration of VTiSbSiOx catalyst for ammoxidation of 3-picoline to nicotinonitrile

摘要

Fresh and industrially spent VTiSbSiOx ammoxidation catalysts were used for nicotinonitrile manufacture from 3-picoline in various catalytic tests.The solid-state characterization of these materials was carried out using different techniques.Catalytic runs with spent samples showed a significant drop in catalytic activity in comparison to the fresh catalyst.However,neither coke-containing deposits nor loss of catalyst components could be detected in the spent samples.X-ray diffraction,nitrogen adsorption,UV/VIS-and EPR-spectroscopy were applied to uncover structural alterations during industrial long-term use and to explore possible reasons for the observed deactivation behavior.Characterization by UV/VIS revealed a partial reduction of vanadium (V) and (IV) towards Vanadium(III).EPR showed structural changes leading to a more pronounced formation of antiferromagnetically interacting vanadium (IV) oxide clusters and,thus,to a loss in vanadium dispersion.A slight increase in crystallinity of the spent samples could be observed by XRD.All these effects collectively lead to the observed deactivation;however,the original activity can be restored by re-oxidation under airflow at 600 °C.By means of regeneration,reduced vanadium species (mainly V(III)) can be partly re-oxidized and the dispersion of the vanadium (IV) oxide clusters can be enhanced again as evidenced by EPR.Interestingly,the catalytic properties of regenerated samples are comparable to the fresh solid.