H2-Induced NO x Adsorption/Desorption over Ag/Al2O3: Transient Experiments and TPD Study

NO adsorption/desorption over 1 wt% Ag/Al2O3 was studied by a combination of isothermal transient adsorption/desorption and NO x temperature-programmed desorption (NO x -TPD) methods. NO x -TPD profiles obtained for Ag/Al2O3 were identified by comparison with decomposition profiles of “model” AgNO3/Al2O3 and Al(NO3)3/Al2O3 prepared by impregnation of Al2O3 with individual AgNO3 and Al(NO3)3 compounds.

The data obtained indicate that H2-induced NO adsorption leads to the formation of surface Ag and Al-nitrates. Their accumulation on the catalyst surface is accompanied by an intensive NO2 evolution, which proceeds primarily via reaction of surface nitrates with NO. Thus, NO2 formation appears to result from an intrinsic stage of the H2-induced NO x adsorption process, rather than from the direct oxidation of NO by gaseous oxygen catalyzed by Ag.