Effect and role of alkali metals added to cobalt ion-exchanged X and Y zeolite catalysts in the gas-phase catalytic oxidation of benzyl alcohol

The effect and the role of the alkali metals added to cobalt ion-exchanged NaX and NaY type zeolties (Co-NaX, Co-NaY) on catalytic activity in the gas-phase catalytic oxidation of benzyl alcohol were studied under various reaction conditions. The alkali metals, impregnated into the Co-NaX and the Co-NaY zeolites, promoted catalytic activity in the partial oxidation measured by the yield of benzaldehyde obtained. The amount of added alkali metal under a constant amount of the ion-exchanged cobalt had an optimal value for the catalytic activity in the partial oxidation. The amount of O2 uptake of the alkali metal/Co-NaX and -NaY zeolites pre-reduced by carbon monoxide was higher than that in their alkali-free counterparts. The catalytic activity in the partial oxidation was correlated with the amount of O2 uptake of the alkali metal/Co-NaX and -NaY zeolites. The comparison between the diffuse reflectance spectra of the Co-NaY catalysts, both with and without added alkali metal, clearly showed that the alkali metal added to the Co-NaY made the oxygen affinity of ion-exchanged Co species more effective and the formation of the cobalt oxides (Co3O4) easier; the cobalt oxides were suggested to be responsible for the partial oxidation of benzyl alcohol.