Evidencing the three cationic coordination vacancies of SIINa+ in NaYzeolite: additional insights from IR surface species

Abstract

The unresolved issue of the maximum number of adsorbed ligands binding to S_II Na⁺ cations contained in a Y zeolite has been investigated and explained using a new experimental approach, specially designed for the specific problem. The formation of Na⁺(CO)₂ di-carbonyls has been identified for the first time for high CO coverage using a survey of IR spectra of the adsorbed CO. Also, the formation of Na⁺(CO)₃ tri-carbonyls is confirmed and the conditions of its formation are thoroughly discussed. Moreover, the adsorption of the CO probe in the large NaY cavities is expressed in terms of four coexisting reactions reflecting the formation of the three Na–carbonyl species which involves the vacant coordination of sodium cations. This study refines the IR vibration bands of the three as-formed carbonyls of interest and provides new information towards the understanding at the molecular scale of how the three free coordination vacancies of Na⁺ sites sitting in S_II positions can be investigated by means of CO binding.