Temperature programmed desorption spectroscopy of N 2H 4 decomposition on Al 2O 3-supported Ir catalyst

Abstract

At room temperature the steady-state decomposition of N 2 H 4 over an alumina-supported Ir catalyst was found to yield NH 3 and N 2 while at temperatures above 800 K the products were N 2 and H 2 . Following exposure of the catalyst surface to N 2 H 4 the adsorbed species were studied by the temperature programmed desorption technique at a heating rate of 2 K s −1 . The desorption products included N 2 , NH 3 and H 2 originating from different binding states. For the more strongly bound nitrogen [N 2 (β 2 )] the kinetics of desorption following exposure to N 2 H 4 are of first-order with a desorption rate constant of 3 × 10 7 exp(−26,800/ RT )s −1 . Adsorption of oxygen on the iridium catalyst was found to decrease the nitrogen binding energy and increase the nitrogen coverage. The surface coverage of all adsorbed species was found to be significantly smaller on catalysts that had been used in pulse mode fuel thrusters. The differences observed were correlated with the loss in metal surface area of the catalyst. However, no differences in the binding energies of the various adspecies were detectable between fresh catalyst and used catalyst.