Oxidation activity of cerium supported NaZSM-5 zeolites with and without added alkali metals in the gas-phase catalytic oxidation of benzyl alcohol

Abstract

The gas-phase catalytic oxidation of benzyl alcohol was carried out over low [Ce_L, ∽1×10^-2 mmol (g-NaZSM-5)^-1] and high [Ce_H, ∽1–2 mmol (g-NaZSM-5)^-1] Ce supported NaZSM-5 zeolites and alkali metal added counterparts. The Ce was supported on NaZSM-5 zeolites by both ion-exchange (Ce_L-NaZSM-5) and impregnation (Ce_L- and Ce_H/NaZSM-5) methods. The alkali metal added to the low and high Ce supported NaZSM-5 catalysts was found to be quite different in influence on the catalytic activity of benzyl alcohol oxidation. The addition of alkali metal to the Ce_L- and/or Ce_L/NaZSM-5 zeolites was found to promote selectively catalytic activity for the partial oxidation of benzyl alcohol. The addition of the alkali metal caused an increase in the amount of O₂ uptake of the prereduced Ce_L- and/or Ce_L/NaZSM-5 catalysts. A correlation was observed between the amount of O₂ uptake and the amount of alkali metal added to the Ce_L- and/or Ce_L/NaZSM-5 catalysts. The alkali metal added to the Ce_L- and/or Ce_L/NaZSM-5 catalysts was suggested to promote the mobility of the oxygen species in the low Ce supported catalysts, whose oxygen species are considered to play an important role in benzaldehyde formation. The alkali metal added to the Ce_H/NaZSM-5 catalysts inversely tended to decrease the oxidation activity. The addition of the alkali metal to the Ce_H/NaZSM-5 catalyst made the particle size of CeO₂ formed in the Ce_H/NaZSM-5 larger, and the redox ability of the oxidic cerium lower through the inhibition of the uptake of O₂.