The role of autoreduction and of oxygen mobility in N 2O decomposition over Fe-ZSM-5

Abstract

The mechanism of N 2O decomposition was studied on a series of Fe-ZSM-5 catalysts prepared by ion exchange (IE) and chemical vapor deposition (CVD). N 2O decomposition activity depends strongly on the extent of autoreduction of the catalyst during the pretreatment in He at high temperatures. The extent of autoreduction is significantly lower for catalysts prepared by CVD compared with that for catalysts prepared by aqueous ion exchange. As a result, the global turnover frequencies of the ion-exchanged catalysts are significantly higher. If the activity is normalized by the concentration of Fe 2+ sites, however, then the CVD catalyst is the most active sample. This is attributed to the fact that high iron loading favors the surface migration and recombination of surface oxygen atoms to O 2, which is the rate-limiting step of the reaction. O 2 formation by slow recombination of two surface oxygen atoms is the dominating mechanism even for IE samples with very low iron loadings.