Isonicotinic acid was directly synthesized by vapor-phase oxidation of 4-picoline over V-Ti-O catalysts prepared by impregnation method. Characterization of the catalysts prepared was carried out by using XRD and the products of the reaction were analyzed by LC and IR. The effects of V loading, promoter, reaction temperature, the space velocity and water quantity on the catalytic performance were investigated. It was found that acidic oxide promoter can improve the catalytic performance and alkaline oxide r...