Surprising Coordination Chemistry of Cu⁺Cations in Zeolites: FTIR Study of Adsorption and Coadsorption of CO, NO, N₂, and H₂O on Cu–ZSM-5

Abstract

Cations exchanged in zeolites are generally characterized by a low coordination number and can thus attach simultaneously more than one small guest molecule. For instance, Cu+ ions in ZSM-5 can accept, at low temperature, up to three CO and up to two NO molecules. However, only one N2 molecule can be coordinated to such sites. Although mixed aqua-carbonyl and aqua-dinitrogen complexes are formed, no mixed carbonyl-nitrosyl, carbonyl-dinitrogen, or nitrosyl-dinitrogen species can be produced. Thus, adsorption of NO on CO precovered sample results in segregation of the CO adsorption layer according to the reaction: 2Cu+–CO + 2NO → Cu+(CO)2 + Cu+(NO)2. Adsorption of N2 on NO precovered sample leads to a similar process: 2Cu+–NO + N2 → Cu+(NO)2 + Cu+–N2. No carbonyl-dinitrogen complexes are produced during CO–N2 coadsorption. The role of the ligand and the nature of the bond in the formation of geminal and mixed-ligand complexes are discussed.