NH4Y Zeolite Research Articles

Assignment of the hydroxyl bands in the infrared spectra of zeolites X and Y. Part 2.—After different pretreatments

The i.r. absorption curve of “deep bed” calcined NH4Y zeolites could be broken down into the same components as HY zeolites. The frequency of the peaks was slightly changed, but their half band width remained constant. In a series of treatments representing increasing hydrolysis non-acidic OH bands around 3680 and 3600 cm–1 increase in intensity, due to surface OH groups near Al defect locations. Polynuclear Al species bridging the cubo-octahedra are suggested to be partly responsible for the increased thermal stability. The non-acidic OH bands in synthetic faujasites exchanged with polyvalent cations are explained on the same basis, since they behave in a similar way as the non-acidic bands on “deep bed” zeolites after different treatments.

The physical properties and catalytic activity of AlHY zeolites

A series of AlHY zeolites has been prepared in which the original sodium ion was replaced by aluminum and hydrogen ions in varying concentrations. These zeolites show greater initial activity for the disproportionation of toluene than an acidic zeolite prepared from NH 4Y zeolite; however, the activity decreases to the level of NH 4Y upon the addition of more toluene. It is possible to introduce up to 16 exchangeable aluminum ions per unit cell, which is more than the number found in an ultrastable zeolite. In contrast to the ultrastable zeolite no aluminum is removed from the lattice during the formation of the AlHY zeolites. The AlHY zeolites are unstable to hydrothermal treatment. Infrared studies show that the number of hydroxyl groups with stretching frequencies at 3640 and 3540 cm −1 decreased as the aluminum exchange increased. No band at 3600 cm −1 was observed. The presence of exposed aluminum ions was confirmed by the EPR spectrum of adsorbed NO and O 2 −.