Katalytický rozklad NO

Abstract

The dissertation thesis deals with direct NO catalytic decomposition to oxygen and nitrogen over K-promoted Co4MnAlOx mixed oxides. 27 samples were prepared using different calcination temperature, calcination time and potassium amount. Physico-chemical properties of prepared catalysts were characterized by AAS, ICP-AES, SBET, XRD, SEM-EDX, TEM, TPR-H2, TPD-CO2, TPD-NO, FTIR, work function and species-resolved thermal alkali desorption. NO decomposition was studied at temperature range of 540-700 °C and GHSV = 6 l g-1 h-1. The inlet gas was composed of 500-8000 ppm NO in N2, in case of measurements in presence of oxygen 0-3 mol.% O2 was added. Calcination temperature and potassium amount significantly affect the physico-chemical properties of prepared catalysts. With increasing calcination temperature and calcination time, the specific surface area and the amount of residual potassium decreases, crystallite size increases, reducibility gets worse, the amount of medium and strong basic sites changes and different phases (KMn8O16, K2Mn4O8 and K1,39Mn3O6) are detected on XRD. With increasing potassium amount, the specific surface area decreases and pores get bigger, the reducibility gets worse and the amount of reducible surface species decreases, the phase composition varies (from KMn8O16 to K2Mn4O8 and K1,39Mn3O6) and the amount of medium and strong basic sites changes. The effect of calcination temperature and potassium amount on NO conversion is not significant for samples with K ≥ 2 wt.%. The NO conversion increases with increasing calcination temperature for samples with K ≤ 2 wt.%. The presence of potassium promotor plays the key role in direct NO decomposition reaction. Alkali metal probably weakens the Co-O bond, which facilitate the desorption of O2 originated from decomposed NO. Non-promoted samples showed no activity which is caused by occupation of active sites by O2, which is not desorbed from catalyst surface. In the presence of oxygen in gas mixture, the catalytic activity significantly decreases with increasing oxygen amount. The effect of calcination time on NO conversion was not proved. All of the promoted samples can be considered as stable regardless the calcination temperature, time and potassium amount. From all tested catalysts, those with 2 wt.% of K calcined at 700 or 800 °C seems to be the most appropriate for the NO decomposition reaction. Based on the experiments performed with the isotopic labeled gas, the reaction mechanism was proposed.