Ru/ZrO2 catalysts II. N2O adsorption and decomposition

Nitrous oxide decomposition studies on an Ru/ZrO2 catalyst (activated by ox idation or reduction at 623 and 773 K) have been performed in a flow reacto r at 1 atm total pressure. The reaction onset temperature is 573 K, while a complete conversion of reactant is achieved at 773 K. At a given temperatu re, the oxidized sample exhibits higher conversions with respect to the red uced one, while an the latter a significant induction period for a stable c onversion with time on stream was observed. In situ FTIR experiments have i ndicated that RuO3 clusters can be found in a dynamic equilibrium with an R uO2 surface layer at the reaction conditions. Ru surface atoms with a valen ce state greater than 4 end tetrahedrically coordinated were found to be ab le to interact with N2O at room temperature. At 773 K, upon introduction of N2O a drastic decrease in the N2O vibrational modes is observed with a sim ultaneous rapid decrease of N2O and increase of O-2 and N-2 in the gas phas e. Tt was concluded that during the reaction N2O acts as a reductant of the oxidized ruthenium surface (Ru6+) sites and as an oxidant of RuO2 (Ru4+) s ites, (C) 2000 Academic Press.