Calorimetric study of N2 adsorption on copper-ion-exchanged ZSM-5 zeolite

Adsorption of nitrogen molecules (N2) at room temperature on a copper-ion-exchanged ZSM-5 zeolite [CuZSM-5(A)] prepared by using an aqueous solution of Cu(CH3COO)2 was examined by measuring the heat of adsorption, IR and emission spectra. The results obtained were compared to those for the samples prepared by using other ion-exchanging solutions such as CuCl2, Cu(NO3)2 and the solution containing [Cu(NH3)2]+ complex ions. It became clear that the N2 adsorption property of the copper-ion-exchanged ZSM-5 zeolites varies depending on the ligands (CH3COO−, Cl−, NO3− and NH3) involved in the copper-ion exchanging solutions, and among these zeolite samples, CuZSM-5(A) has the most efficient adsorption property (i.e., strong adsorption) for N2 molecules. The emission spectra revealed that there exist at least two types of Cu+ species on the CuZSM-5(A) sample; the Cu+ species that gives a band at 535 nm interact strongly with N2 molecules, while those giving a band at 475 nm are inactive for N2 adsorption. The heat of adsorption of N2 on the former type of Cu+ species was found to be 80 kJ mol−1, being much larger than those observed for usual metal oxides.