Kinetics of Oxygen Exchange and N2O Decomposition Reaction over MeOx/CeO2 (Me = Fe, Co, Ni) Catalysts

Abstract

MeOx/CeO2 (Me = Fe, Co, Ni) samples were tested in an 18O2 temperature-programmed isotope exchange and N2O decomposition (deN2O). A decrease in the rate of deN2O in the presence of oxygen evidences the competitive adsorption of N2O and O2 on the same sites. A study of isotope oxygen exchange revealed dissociative oxygen adsorption with the subsequent formation of surface oxygen species. The same species, more probably, result from N2O adsorption and the following N2 evolution to the gas phase. We supposed the same mechanism of O2 formation from surface oxygen species in both reactions, including the stages responsible for its mobility. A detailed analysis of the kinetics of isotope exchange has been performed, and the rates of one-atom (RI) and two-atom (RII) types of exchange were evaluated. The rate of the stage characterizing the mobility of surface oxygen was calculated, supposing the same two-step mechanism was relevant for both types of exchange. The effect of oxygen mobility on the kinetics of deN2O was estimated. An analysis of the possible pathways of isotope transfer from MeOx to CeOx showed that direct oxygen exchange on the Me–Ce interface makes a valuable contribution to the rate of this reaction. The principal role of the Me–Ce interface in deN2O was confirmed with independent experiments on FeOx/CeO2 samples with a different iron content.

NiCoAl-Based Monolithic Catalysts for the N2O Intensified Decomposition: A New Path towards the Microwave-Assisted Catalysis

“…The N 2 O decomposition reaction mechanism involves the production of oxygen atoms adsorbed on the catalyst that form O 2 and desorb [42]. As a result, the reducibility of the catalytic species is highly relevant for the process at issue.…”

“…According to the reaction mechanism reported in Ref. [42], the N2O molecule reacts with an active site producing molecular N2 and obtaining an activated atomic oxygen (O*) whose combination with another (O*) generates O2, with the release of two active sites, according to the Langmuir-Hinshelwood mechanism. It is clear that the higher the N2O concentration, the lower the number of available active sites, consequently limiting the decomposition reaction.…”

“…Thus, greatly increasing the reactant concentration could change the reaction rate kinetic. According to the reaction mechanism reported in Ref [42],. the N 2 O molecule reacts with an active site producing molecular N 2 and obtaining an activated atomic oxygen (O*) whose combination with another (O*) generates O 2 , with the release of two active sites, according to the Langmuir-Hinshelwood mechanism.…”