DFT Study of NO Reduction Process on Ag/γ-Al2O3 Catalyst: Some Aspects of Mechanism and Catalyst Structure

Vitaly E Matulis,Oleg A Ivashkevich,Ekaterina G Ragoyja,Dmitry A Lyakhov,Dominik Michels

doi:10.1021/acs.jpcc.0c08417

Abstract

Catalysts based on Ag/γ-Al2O3 are perspective systems for practical implementation of catalytic NO reduction. Nevertheless, the mechanism and regularities of this process have still not been fully investigated. Herein, we present the results of quantum-chemical research of the Ag/γ-Al2O3 catalyst surface and some aspects of the NO reduction mechanism on it. Proposed calculation methods using DFT and cluster models of the catalyst surface are compared and verified. The possibility of existence of small adsorbed neutral and cationic silver clusters on the surface of the catalyst is shown. It is demonstrated that NO adsorption on these clusters is energetically favorable, in the form of both monomers and dimers. The scheme of NO selective catalytic reduction (SCR) that explains increasing of N2O side-product amount on catalysts with silver fraction more than 2 wt % is proposed. The feasibility of this scheme is justified with calculated data. Some recommendations that allow decreasing amounts of N2O are developed.

Highlights

Our results show that embedded cluster models 4 and 5 predict adsorption energy values that are comparable with data of periodic calculations (Table 1)
Our data shows that the most reliable results could be obtained within embedded cluster models with “soft” charges
Our results show that proposed embedded cluster models allow to obtain results that are comparable with data of periodic calculations, but with much less computational cost

Summary

Introduction

The problem of deteriorating of air quality caused by increasing emission of road transport exhaust gases is especially urgent nowadays. Many researchers are focused on development of new effective catalysts for afterburning of fuel residues and reduction of nitrogen oxides. It has been shown that silver particles adsorbed on the surface of aluminium oxide catalyze the selective reduction of nitrogen oxides.[1]. The catalytic activity of such systems depends on the size and the charge of the adsorbed silver particles. It is important to know how these characteristics affect the SCR process. Based on the results of experimental and theoretical investigations Deng et al[2] have shown that for high efficiency of the SCR process, the optimal concentration of silver in the catalyst should be within

Objectives

Results

Conclusion