Cu-Mg-Fe-O-(Ce) Complex Oxides as Catalysts of Selective Catalytic Oxidation of Ammonia to Dinitrogen (NH3-SCO)

Kamil Górecki,Kateřina Pacultová,Sylwia Górecka,Aneta Smýkalová,Katarzyna Pamin,Lucie Obalová

doi:10.3390/catal10020153

Abstract

Multicomponent oxide systems 800-Cu-Mg-Fe-O and 800-Cu-Mg-Fe-O-Ce were tested as catalysts of selective catalytic oxidation of ammonia to dinitrogen (NH3-SCO) process. Materials were obtained by calcination of hydrotalcite-like compounds at temperature 800 °C. Some catalysts were doped with cerium by the wet impregnation method. Not only simple oxides, but also complex spinel-like phases were formed during calcination. The influence of chemical composition, especially the occurrence of spinel phases, copper loading and impregnation by cerium, were investigated. Materials were characterized by several techniques: X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), low-temperature nitrogen adsorption (BET), cyclic voltammetry (CV), temperature programmed reduction (H2-TPR), UV-vis diffuse reflectance spectroscopy and scanning electron microscopy (SEM). Examined oxides were found to be active as catalysts of selective catalytic oxidation of ammonia with high selectivity to N2 at temperatures above 300 °C. Catalysts with low copper amounts (up to 12 wt %) impregnated by Ce were slightly more active at lower temperatures (up to 350 °C) than non-impregnated samples. However, when an optimal amount of copper (12 wt %) was used, the presence of cerium did not affect catalytic properties. Copper overloading caused a rearrangement of present phases accompanied by the steep changes in reducibility, specific surface area, direct band gap, crystallinity, dispersion of CuO active phase and Cu2+ accessibility leading to the decrease in catalytic activity.

Highlights

Ammonia, besides nitrogen and sulfur oxides, non-methane volatile organic compounds and fine particulate matter (PM2.5 ), belongs to the group of air pollutants whose emissions are strictly monitored, and for which long-term emission reduction programs were introduced (e.g., National Emission CeilingsDirective 2001/81/EC (NECD) and Gothenburg Protocol)
Our research shows that the proposed oxide systems are active as catalysts of selective catalytic oxidation of ammonia; neither Ce modified, or unmodified catalysts reached 100% of ammonia conversion
The prepared mixed metal oxides were tested as catalysts of low-temperature selective catalytic oxidation of ammonia to dinitrogen

Summary

Introduction

Besides nitrogen and sulfur oxides, non-methane volatile organic compounds and fine particulate matter (PM2.5 ), belongs to the group of air pollutants whose emissions are strictly monitored, and for which long-term emission reduction programs were introduced (e.g., National Emission CeilingsDirective 2001/81/EC (NECD) and Gothenburg Protocol). On the basis of the most recent data, ammonia emissions have been estimated at about 5 600 kt y−1 [1]. The main sources of emissions include agriculture (comprises 94% of total emissions [2]), industry (including energy production and use), road transport and waste [2,3,4,5]. Environmental reports show that total emissions of ammonia, thanks. There are sectors where ammonia emissions increased drastically in recent years, and a further increase is expected. These are transportation and stationary sources equipped with selective catalytic reduction (SCR)

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