Kinetic and infrared spectroscopic studies of Fe-Y zeolites for the selective catalytic reduction of nitric oxide by ammonia

Reaction kinetics and infrared spectroscopic studies of the selective catalytic reduction of nitric oxide by ammonia were conducted at reactant concentrations near 500 ppm and temperatures from 473 to 623 K, over Fe-Y zeolites having Si/Al ratios of 2.4, 3.2, and 4.4. The presence of iron cations within the zeolite was necessary to sustain steady-state catalytic activity, which was enhanced by about two orders of magnitude in the presence of oxygen. The reaction was near first order in NO and near zero order in ammonia. Ammonia oxidation was found to become a significant competing reaction between 493 and 543 K over zeolites with Si/Al ratios equal to 2.4 and 3.2. Ammonia oxidation did not occur over the sample with a Si/Al ratio of 4.4. The primary surface species observed under reaction conditions by in situ IR spectroscopy were NH3 and NH+4 In the absence of oxygen, the rate-limiting step appears to be the reoxidation of iron.