Surface potassium promotion of Co4MnAlOx in direct NO decomposition generates the same type of active sites as bulk promotion

Abstract

K/Co4MnAlOx mixed oxides are active in direct NO decomposition. This work investigates the effect of the preparation method and K precursor type. Using the incipient wetness impregnation method, the modification by the required amount of K was ensured. Regardless of the K precursor type, similar NO conversions were reached for samples modified by 4 wt % K. The optimal amount of K from the KNO3 precursor was evaluated as 2–6 wt %. The physicochemical properties were carefully explored using atomic absorption spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transform IR spectroscopy, N2 physisorption, H2 temperature-programmed reduction, CO2 and NO temperature-programmed desorption, scanning electron microscopy, and transmission electron microscopy, correlated with catalytic properties in transient and steady state and compared with the results obtained in our previous study using bulk modified samples. The present study underlines the effect of the preparation method on the Brunauer–Emmett–Teller surface area (SBET) of prepared catalysts and thus the amount of active sites available for catalytic reaction. Moreover, the results emphasize the importance of catalyst basicity, which affects the amount of adsorbed NO2– species, the key intermediates in the direct NO catalytic reaction.