Calorimetric study of room temperature adsorption of N 2O and CO on Cu(II)-exchanged ZSM5 zeolites

Abstract

Copper ion-exchanged ZSM5 zeolites have been prepared with different cooper loadings from under- to over-exchanged levels. The adsorptions of N 2O and CO at 303 K have been studied using calorimetric method and infrared spectroscopy. The samples were additionally characterised by ammonia adsorption at 423 K. The active sites for both N 2O and CO are Cu(I) ions, which were formed as a result of pre-treatment in vacuum at 673 K. Room temperature adsorption of nitrous oxide at low equilibrium pressures (up to 66.7 Pa) resulted in small amounts of chemisorbed N 2O (<0.2 molecule per one Cu ion). Differential heats of N 2O adsorption between 80 and 30 kJ/mol were obtained. Differential heats of CO adsorption between 140 and 40 kJ/mol were obtained. The obtained amounts of chemisorbed species in the investigated systems and the values of differential heats of both nitrous oxide and carbon monoxide demonstrate the dependence on the copper content.