Copper Aluminum Spinels Doped with Cerium as Catalysts for NO Removal

Anna Białas,Kamil Rugała,Jacek Gurgul,Grzegorz Mordarski,Cezary Czosnek

doi:10.3390/catal10121388

Abstract

Cu-Ce(Mn)-Al oxide catalysts to NO removal in the broad temperature range were synthesized and tested. The precursor of copper aluminium spinel was obtained with the coprecipitation method. By this method, Cu–Al spinels with various amounts of manganese and cerium were synthesized as well. These oxides crystallized in the structure of inverse spinel; however, Ce doping caused the appearance of additional CeO2 phase as determined by XRD. The samples were mesoporous solids with moderate surface area and porosity measured by low temperature sorption of nitrogen. The addition of another metal to Cu–Al spinel caused an increase of activity in selective catalytic reduction of nitrogen oxide with ammonia. The presence of manganese caused the formation of a higher amount of N2O by-product. The catalytic activity increased with the cerium concentration. For the sample with the atomic ratio Ce0.15Cu0.18, ca. 90% of NO conversion was registered between 200 and 350 °C. As examined with XPS spectroscopy, such conversion was attained due to the good dispersion of copper on the catalyst surface. This copper was placed mainly in spinel octahedral positions which enable its easier reduction. The spinel structure causes the presence of cerium as the trivalent cation important in redox cycles with the participation of copper.

Highlights

Nitrogen oxides (NOx ) are one of the main air pollutants that form during fuel burning.Their Selective Catalytic Reduction (SCR) with ammonia is applied to remove them from off-gases from the stationary sources of emission [1]
The replacement of copper by cerium in the Ce0.03 Cu0.30 sample caused a slight increase in the catalytic efficiency at lower temperatures (150–250 ◦ C) and a more distinct decrease above 400 ◦ C
The precursor of mixed copper–aluminum oxide with the molar ratio 2:1 was obtained with the coprecipitation method

Summary

Introduction

Nitrogen oxides (NOx ) are one of the main air pollutants that form during fuel burning Their Selective Catalytic Reduction (SCR) with ammonia is applied to remove them from off-gases from the stationary sources of emission [1]. During this process, nitrogen and water are expected products like in the following reactions: nitrous oxide is often formed as well, according to the reaction equations: Catalysts 2020, 10, 1388; doi:10.3390/catal10121388 www.mdpi.com/journal/catalysts. Nitrogen and water are expected products like in the following reactions: nitrous oxide is often formed as well, according to the reaction equations: Catalysts 2020, 10, 1388; doi:10.3390/catal10121388 www.mdpi.com/journal/catalysts This greenhouse gas influences the global warming about 300 hundred times stronger than carbon dioxide. Such catalysts can be obtained by the deposition of an active phase on a support or by its coprecipitation with metal ions improving its properties

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