Influence and role of added alkali metals on the gas-phase oxidation of benzyl alcohol catalyzed by Cu ion-exchanged NaX zeolites

Abstract

The influence and the role of alkali metals added to Cu ion-exchanged NaX (Cu–NaX) catalysts on the gas-phase catalytic oxidation of benzyl alcohol were examined based on the oxidation results, O₂ uptakes and insitu IR measurements. The addition of alkali metals to the Cu–NaX catalyst particularly promoted the catalytic activity for partial oxidation. The dependence of the percentage of Cu ion exchange of the alkali metal-added Cu–NaX catalyst on the catalytic activity in the benzyl alcohol oxidation and the effect of the added alkali metal/Cu ratio on the oxidation activity confirmed that the alkali metals added to the Cu–NaX catalyst contributed to an increase in the yield of benzaldehyde, while prohibiting an increase in the yield of carbon dioxide. The added alkali metals present in the spatial vicinity of the Cu ions functioned more effectively for the promotion of the partial oxidation. The O₂ species sorbed on the catalyst during the benzyl alcohol oxidation was suggested to contribute to the production of benzaldehyde. The O₂ uptake of the alkali metal-added Cu–NaX catalyst, which was pre-treated at 773 K under a CO atmosphere, became greater than that of the Cu–NaX counterpart without the added alkali metal. The alkali metal-added Cu–NaX catalyst was directly observed to produce a partial oxidation product under milder conditions than the Cu–NaX catalyst based on insitu IR measurements. The alkali metals added to the Cu–NaX catalyst will play an important role in increasing the O₂ uptake, of which the sorbed O₂ species will participate in the partial oxidation of benzyl alcohol.