Both benzoic acid and benzaldehyde are important chemicals in the organic synthesis industry. Liquid-phase oxidation of toluene by air is an environmental benign method to produce benzoic acid and benzaldehyde in the modern industry. In this process, cobalt salt is employed as the catalyst. Its contents and valence state directly influence the progress and performance of the reaction. So, from the view of mechanism research, it is important to detect the existence states of the cobalt ions in o...