Theoretical models for NO decomposition in Cu-exchanged zeolites

TL;DR

This paper develops a theoretical framework for NO decomposition in Cu-exchanged zeolites, incorporating system interactions and zeolite vibrations, and compares predictions with experimental data to elucidate active site characteristics.

Contribution

It introduces a unified theoretical model for NO decomposition in Cu-zeolites, considering both monomolecular and bimolecular mechanisms with memory effects.

Findings

Theoretical rate constants align with experimental data.

Different catalytic roles of Cu+ ions and zeolite vacancies identified.

Model provides insights into active site geometry and energetics.

Abstract

A unified description of the catalytic effect of Cu-exchanged zeolites is proposed for the decomposition of NO. A general expression for the rate constant of NO decomposition is obtained by assuming that the rate-determining step consists of the transferring of a single atom associated with breaking of the N-O bond. The analysis is performed on the base of the generalized Langevin equation and takes into account both the potential interactions in the system and the memory effects due to the zeolite vibrations. Two different mechanisms corresponding to monomolecular and bimolecular NO decomposition are discussed. The catalytic effect in the monomolecular mechanism is related to both the Cu+ ions and zeolite O-vacancies, while in the case of the bimolecular mechanism the zeolite contributes through dissipation only. The comparison of the theoretically calculated rate constants with experimental results reveals additional information about the geometric and energetic characteristics of the active centers and confirms the logic of the proposed models.