Hydroxide groups on zeolites. I

The CaNaY and MgNaY zeolites were investigated for the number and properties of hydroxyl groups as a function of the degree of exchange through D2 exchange, using infrared spectroscopy. Five types of hydroxyl groups exist on these zeolites, differing in their concentration, acidity, and thermal stability. The OH groups predominantly arise from dissociative chemisorption of water onto the divalent cations. The concentration of the OH groups is characteristically dependent on the degree of exchange. There are OH groups that are strong acidic Brønsted centers capable of protonating pyridine, and those that only exhibit weak interactions with pyridine. The number of acidic Brønsted centers increases in parallel with the total number of hydroxyl groups as the degree of exchange increases, and it is strongly dependent on the type of exchanged cations and the preheating temperature. MgNaY zeolites possess more and thermally stable hydroxyl groups than CaNaY zeolites.