Nanesené tvarované katalyzátory na bázi směsných oxidů kobaltu pro rozklad N2O

Abstract

This Ph. D. thesis focuses on the research of supported catalysts based on cobalt mixed oxides for low temperature N2O decomposition applicable in the reduction of N2O emissions from HNO3 production plants. The first part of this work focuses on the study of laboratory reactors for shaped catalyst testing. Catalytic test conditions suitable for obtaining kinetic data not affected by macro kinetic elements, which would allow direct data transfer to a larger scale, were determined. In the second part of this thesis, cobalt catalysts deposited on different commercial supports in the pelletized and open-cell foam form were studied for N2O decomposition. The relationship between the method of catalyst preparation, their physico-chemical properties evaluated by available methods (AAS, BET, XRD, SEM, FTIR, Raman, Hg-porosimetry, H2-TPR) and catalytic properties were studied. In the case of Co3O4 deposited on the different kinds of pelletized supports (TiO2, Al2O3, and Mg-Al mixed oxides with various Mg and Al), it was found that Co3O4 deposited on a support with a high content of Mg possessed the highest catalytic activity among the supported samples, in spite of the fact that it contained hardly reducible compounds. This can be explained by the presence of active sites with easier reducibility and better dispersion of active phase on the surface of the support. The part dealing with cobalt based catalyst deposited on the open-cell ceramic foam consists of the following steps: • Determination of the optimal preparation method: Co3O4 and Co4MnAlOx were deposited on the SiC open-cell foams by wet impregnation and suspension methods. Suspension method provides active phase with higher surface areas and sites with better reducibility, both of these factors contribute to higher N2O conversions. However, the layer of active phase prepared by suspension method has worse adhesion to support, due to catalyst layer cracking. • Determination of a suitable kind of ceramic foam material: Co3O4-Cs was deposited on the different kinds of ceramic foams (Al-Si, Zr-Mg-Al and SiC-Al). Samples on the SiC-Al and Zr-Mg-Al supports showed lower catalytic activity in comparison to samples on the Al-Si support, which could be related to worse dispersion of active phase on these supports and interaction of active phase with support material. • Determination of the optimal number of catalyst layers on the ceramic foam supports: Co3O4-Cs and Co4MnAlOx-K were deposited on the ceramic foams with different numbers of deposited catalyst layers. Application of several active layers, in order to increase the amount of active phase in the catalyst, leads to the reduction of active sites' accessibility in catalytic reaction and did not lead to an increase in catalytic activity. • Optimization of catalyst preparation in order to increase catalyst surface area by applying different interlayers: Co3O4-Cs was deposited on the ceramic foams already coated by different interlayers (MgO, Mn2O3, SiO2 and TiO2). The use of chosen interlayers led to worse dispersion of active phase on the support and changes in reducibility. In the last part of the dissertation, supported catalysts with the highest catalytic activity and unsupported commercial pellets AST-4 with the same chemical composition of active phase were compared by mathematical modeling of the full scale reactor for N2O abatement in waste gas from HNO3 production plants to evaluate the catalytic activity in industry conditions.