Magnesium Effect in K/Co-Mg-Mn-Al Mixed Oxide Catalyst for Direct NO Decomposition

Kateřina Karásková,Paweł Stelmachowski,Kateřina Pacultová,Květuše Jirátová,Dagmar Fridrichová,Anna Klegova,Lucie Obalová,Marta Valášková,Andrzej Kotarba

doi:10.3390/catal10080931

Abstract

Emission of nitric oxide represents a serious environmental problem since it contributes to the formation of acid rain and photochemical smog. Potassium-modified Co-Mn-Al mixed oxide is an effective catalyst for NO decomposition. However, there are problems related to the thermal instability of potassium species and a high content of toxic and expensive cobalt. The reported research aimed to determine whether these shortcomings can be overcome by replacing cobalt with magnesium. Therefore, a series of Co-Mg-Mn-Al mixed oxides with different Co/Mg molar ratio and promoted by various content of potassium was investigated. The catalysts were thoroughly characterized by atomic absorption spectroscopy (AAS), temperature-programmed reduction by hydrogen (TPR-H2), temperature-programmed desorption of CO2 (TPD-CO2), X-ray powder diffraction (XRD), N2 physisorption, species-resolved thermal alkali desorption (SR-TAD), and tested in direct NO decomposition with and without the addition of oxygen and water vapor. Partial substitution of magnesium for cobalt did not cause an activity decrease when the optimal molar ratio of K/Co on the normalized surface area was maintained; it means that the portion of expensive and toxic cobalt can be successfully replaced by magnesium without any decrease in catalytic activity.

Highlights

Nitrogen oxides (NOx ) are harmful to the human body but are responsible for photochemical smog and acid rain
The chemical composition of catalysts calcined at 700 ◦ C was determined by atomic absorption spectroscopy (AAS) (Table 1)
For the 2K/Mgi catalysts, except for the 2K/Mg2.2 sample, some small differences in potassium content ranging from 1.4 to 1.8 wt. % of potassium were observed despite having constant nominal K content of wt. %

Summary

Introduction

Nitrogen oxides (NOx ) are harmful to the human body but are responsible for photochemical smog and acid rain. Other sources of NOx emissions are chemical processes in which these oxides are present. Direct catalytic decomposition of nitrogen oxides into N2 and O2 offers the most ideal route for NOx removal from waste gases and is both versatile and economic because no reductants (such as NH3 , urea, CO, or hydrocarbons) are required. The catalytic activities of catalysts described in literature until now are insufficient, in the presence of other gases such as O2 and CO2. For this reason, studies of catalytic decomposition of NO worldwide are still in the stage of basic laboratory

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