The mechanism of temperature-programmed desorption (TPD) of nitric acid chemisorbed on BaNa-Y was studied over the temperature range from 200 to 400°C, in the presence and absence of CO. Nitric acid dissociates to form H+ and NO3- when chemisorbed on BaNa-Y. The results of these experiments are consistent with H+ and NO 3- either reacting directly to produce OH and NO 2 or recombining to produce HNO3, which is desorbed and rapidly decomposes within the zeolite pores to OH and NO2. The kinetics and stoichiometry suggest that the hydroxyl radicals produced react with CO and NO2 to form CO2 + H and NO + HO2, respectively. The H atoms thus formed react with OH in preference to NO 2, a change in mechanism consistent with literature rate constants and the expectation that the zeolite pore walls act as a third body for the reaction of H with OH. Finally, OH may react with NO2 to form HO 2, which can undergo further reactions to form O2, H 2O, and/or H2. No reaction between CO and NO3 or CO and surface-bound NO3- was observed.
ASJC Scopus subject areas
- General Physics and Astronomy
- Physical and Theoretical Chemistry