TPD of NO2− and NO3− from Na-Y: The relative stabilities of nitrates and nitrites in low temperature DeNOx catalysis

Temperature programmed depletion (TPD) was performed for both surface nitrates (H+–NO3−) and surface nitrites (H+–NO2−) on Na-Y. The depletion curves are each adequately described with a pre-exponential of 1013 and activation energies that vary as a function of coverage from ∼100 to 200 kJ mol−1. Multiple adsorption sites could lead to the observed variation in activation energies. NO2− is more kinetically stable than NO3− on Na-Y. The effect that the method of preparation of NO3− and NO2− could have on the relative stabilities of the nitrates and nitrites is discussed. The trends for the relative stabilities of different nitrates and nitrites on Na-Y and BaNa-Y are examined as a function of the cationic adsorption site and the counter-ion (e.g., H+ and NO+). The possible roles of the stabilities of nitrates and nitrites in low temperature DeNOx catalysis are considered.