Bimetallic AgFe Systems on Mordenite: Effect of Cation Deposition Order in the NO Reduction with C3H6/CO

Perla Sánchez-López,Serguei Miridonov,Fernando Chávez-Rivas,Sergio Fuentes,Vitalii Petranovskii,Yulia Kotolevich

doi:10.3390/catal9010058

Abstract

Mono- and bimetallic systems of Ag, Fe, and Ag–Fe exchanged in sodium mordenite zeolite were studied in the reaction of NO reduction. The transition metal cations Ag and Fe were introduced by ion exchange method both at room temperature and 60 °C; modifying the order of component deposition in bimetallic systems. These materials were characterized by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), ultraviolet-visible spectroscopy (UV-Vis), X-Ray photoelectron Spectroscopy (XPS) and High-resolution transmission electron microscopy (HR-TEM). The XPS and UV–Vis spectra of bimetallic samples revealed that under certain preparation conditions Ag+ is reduced with the participation of the Fe2+/Fe3+ ions transition and is present in the form of a Ag reduced state in different proportions of Agm clusters and Ag0 NPs, influenced by the cation deposition order. The catalytic results in the NO reduction reaction using C3H6/CO under an oxidizing atmosphere show also that the order of exchange of Ag and Fe cations in mordenite has a strong effect on catalytic active sites for the reduction of NO.

Highlights

In recent decades, there has been considerable interest from regulatory organizations and the scientific community in solving environmental issues associated with NOx emissions
The bimetallic systems were prepared in three different ways varying the order of incorporation of Ag+ and Fe2+ cations as follows: (1) Single stage ion-exchange from a binary mixture solution when Ag and Fe-containing solutions were mixed in a volume ratio of 1:1; (2) double-stage ion-exchange, Ag first, Fe; (3) double-stage ion-exchange, Fe first, Ag
The characterization of the bimetallic catalysts allowed the identification of Fe and Ag ions and metal species with different degree of concentration, aggregation, and environment, which led to different catalytic behavior of the catalysts in the reduction of NO

Summary

Introduction

There has been considerable interest from regulatory organizations and the scientific community in solving environmental issues associated with NOx emissions. Various technologies and processes for removing NOx emissions from exhaust gases have been developed [2,3,4,5]. The selective catalytic reduction of NOx (SCR of NOx ) with ammonia or light hydrocarbons as reducing agents is one of the promising ways to remove nitrogen oxides from mobile exhaust sources [6,7,8,9]. As catalysts for NOx reduction, are used transition metal cations and multi-metallic mixtures (Fe3+ , Co2+ , Ni2+ , Cu2+ , Zn2+ , Ag+ , and others), supported on various carriers, including zeolites [10,11,12,13,14,15]. The unique physicochemical properties of the zeolites, such as their controlled acidity, adsorption capacity, ion exchange properties, and thermal stability, as well as uniform channels and cavities crystallographically ordered in size and position determine their effectiveness in catalytic

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