CATALYSIS OF CU(II)-NAZSM-5 ZEOLITES DURING BENZYL ALCOHOL OXIDATION

The vapor-phase oxidation of benzyl alcohol over copper(II) ion-exchanged NaZSM-5 type zeolites (Cu(II)-NaZSM-5) was studied. The major products were benzaldehyde and carbon oxides (CO2 + CO). The Cu(II)-NaZSM-5 catalysts showed higher catalytic activity for benzyl alcohol oxidation than the corresponding Y type zeolites. The influence of reaction temperature and the degree of Cu(II) ion exchange on the catalytic activity and the selectivity in the benzyl alcohol oxidation was investigated. From the kinetic results, the formation rate of benzaldehyde was found to be first order with respect to the partial pressure of benzyl alcohol and the reciprocal of first order with respect to the partial pressure of oxygen. The Cu(II) ions in the Cu(II)-NaZSM-5 zeolites were found to be easily reduced by degassing at higher temperatures. On the basis of the IR spectra of benzyl alcohol adsorbed on the Cu-NaZSM-5 zeolites, which were treated under oxidizing and/or reducing atmospheres, the oxidation of benzyl alcohol to benzaldehyde was suggested to proceed by the one-electron redox process of the copper ions. A reaction scheme is proposed in which the Cu(II) ion and/or Cu(II)-O2- adduct in the NaZSM-5 zeolite seem/seems to react with benzyl alcohol adsorbed on the Cu(II) ion to give benzaldehyde and the Cu(I) ion, which is rate-determining. The reduced Cu(I) ion can be readily reoxidized to the Cu(II) ion by molecular oxygen.