Catalytic activity of NaZSM-5 supported Cu catalysts with or without added alkali metal in benzyl alcohol oxidation

Abstract

The vapour-phase catalytic oxidation of benzyl alcohol has been carried out over NaZSM-5 supported copper and alkali-metal-added NaZSM-5 supported Cu catalysts. The NaZSM-5 zeolite supported copper catalyst has been prepared by three different methods, impregnation (Cu_imp1/NaZSM-5), modified impregnation (Cu_imp2/NaZSM-5) and also ion-exchange (Cu_ex–NaZSM-5) methods. The preparation method of the NaZSM-5 supported Cu catalyst influenced the oxidation activity of the catalysts, regardless of the alkali-metal addition. The NaZSM-5 supported copper catalyst (Cu_imp1/NaZSm-5) prepared by the impregnation method was found to show the highest oxidation activity among the prepared catalysts. Addition of alkali–metal to the NaZSM-5 supported Cu catalysts prepared by the different methods enhanced the oxidation activity, particularly the partial oxidation activity of the Cu-NaZSM-5 catalysts. The Na ions originally present in the NaZSM-5 support which maintain the charge neutrality were found not to affect substantially the catalytic activity. The redox behaviour and the structure of the Cu species anchored in the NaZSM-5 support were investigated using O₂ uptake, CO adsorption and XRD measurements. The interaction of the Cu species impregnated in the NaZSM-5 zeolite with O₂ was promoted by adding alkali metals. The alkali metals added to the Cu_imp/NaZSM-5 zeolites were suggested to enhance the formation of the oxidic Cu species, which are considered to be responsible for the oxidation activity.

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