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.