Ferrierite and Its Delaminated and Silica-Intercalated Forms Modified with Copper as Effective Catalysts for NH3-SCR Process

Aneta Święs,Andrzej Kowalczyk,Antonio E. Palomares,Lucjan Chmielarz,Urbano Díaz,Małgorzata Rutkowska

doi:10.3390/catal10070734

Abstract

The main goal of the study was the development of effective catalysts for the low-temperature selective catalytic reduction of NO with ammonia (NH3-SCR), based on ferrierite (FER) and its delaminated (ITQ-6) and silica-intercalated (ITQ-36) forms modified with copper. The copper exchange zeolitic samples, with the intended framework Si/Al ratio of 30 and 50, were synthetized and characterized with respect to their chemical composition (ICP-OES), structure (XRD), texture (low-temperature N2 adsorption), form and aggregation of deposited copper species (UV-vis-DRS), surface acidity (NH3-TPD) and reducibility (H2-TPR). The samples of the Cu-ITQ-6 and Cu-ITQ-36 series were found to be significantly more active NH3-SCR catalysts compared to Cu-FER. The activity of these catalysts in low-temperature NH3-SCR was assigned to the significant contribution of highly dispersed copper species (monomeric cations and small oligomeric species) catalytically active in the oxidation of NO to NO2, which is necessary for fast-SCR. The zeolitic catalysts, with the higher framework alumina content, were more effective in high-temperature NH3-SCR due to their limited catalytic activity in the side reaction of ammonia oxidation.

Highlights

Nitrogen oxides (NOx ) belong to the most dangerous air pollutants responsible for various environmental problems, such as photochemical smog, acid rain and ozone depletion
It can be seen that the intensity of the band characteristic of NO2 is higher for the Cu-ITQ-6 and Cu-ITQ-36 catalysts than for the Cu-FER samples
It was shown that copper modified ITQ-6 and ITQ-36 zeolites effectively operated in NH3 -SCR in much broader temperature ranges compared to the Cu-FER catalysts

Summary

Introduction

Nitrogen oxides (NOx ) belong to the most dangerous air pollutants responsible for various environmental problems, such as photochemical smog, acid rain and ozone depletion. Among the post-combustion technologies of NOx emission control, the selective catalytic reduction of nitrogen oxides with ammonia (NH3 -SCR) is one of the most important methods. In this case, NOx present in flue gases are selectively reduced by ammonia to dinitrogen and water vapor, which are the desired products of this process. NOx present in flue gases are selectively reduced by ammonia to dinitrogen and water vapor, which are the desired products of this process This technology was first applied in Japan in the 1970s for the conversion of NOx emitted by electric power stations and has since spread to the USA, Europe and several Asian countries [2]. At temperatures below 300 ◦ C, the efficiency level of NOx conversion is not satisfying, Catalysts 2020, 10, 734; doi:10.3390/catal10070734 www.mdpi.com/journal/catalysts

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