ROLES OF ALKALI-METAL ADDED TO CU-NAZSM-5 CATALYSTS IN THE OXIDATION OF BENZYL ALCOHOL

Alkali-metal addition to Cu-NaZSM-5 zeolite promotes oxidation activit y (mainly partial oxidation rather than complete oxidation) using benz yl alcohol oxidation as a model reaction. The alkali-metal added to Cu -NaZSM-5 is present as the corresponding oxide, such as Na2O. The perc entage of Cu ion exchanged and the added Na/Cu atomic ratio in Na-adde d Cu-NaZSM-5 are important factors governing the oxidation activity. T he added alkali-metal is suggested to be located in the neighbourhood of the Cu species as ligands, rather than covering the Cu species in C u-NaZSM-5 zeolite. The influence of added Na on the adsorption and red ox properties of Cu-NaZSM-5 zeolite were investigated to shed light on the role of the added alkali-metal during oxidation by means of ethan ol and CO adsorptions, O-2 uptake, TPD of ethanol and temperature-prog rammed reaction, in addition to the results of the oxidation reaction. The amounts of O-2 uptake by the prereduced Na-added Cu-NaZSM-5 were considerably larger than those by the corresponding Cu-NaZSM-5 without alkali-metal. The added alkali-metal is considered to help accommodat e the adsorbed oxygen species, which is dissociated and is responsible for the partial oxidation of benzyl alcohol. The added alkali-metal a lso allows the Cu-I species to be more easily oxidized and to adsorb g reater amounts of reactant alcohol; this explains the promotion effect of the added alkali-metal observed in the gas-phase catalytic oxidati on of benzyl alcohol.