Active sites in zeolites. V. Hydrogen--deuterium equilibration over synthetic faujasites

The rate of isotopic exchange between H2 and D2 was followed over NaY, NaX, HY, hydrolyzed HY and LaY zeolites with controlled amounts of iron impurities. Two maxima have been observed in the equilibration rates, one after activation at 5200C, and another at 6700C. At the two maxima, a linear correlation was found between equilibration rates and the iron content of the respective catalysts. The active sites at the first maximum were assumed to be cationic iron, while the activity at the second maximum was ascribed to an iron oxide species. Evaluation of the kinetic parameters showed that the data are consistent with a Bonhoeffer--Farkas mechanism