Reaction mechanism of NO direct decomposition over K-promoted Co-Mn-Al mixed oxides – DRIFTS, TPD and transient state studies

Abstract

The reaction mechanism of direct NO decomposition over Co4MnAlOx mixed oxides prepared by co-precipitation method and promoted by 0-3.1 wt.% of potassium was studied. Temperature programmed desorption of NO and in-situ diffuse reflectance infrared Fourier transform spectroscopy confirmed the presence of several nitrogen species (adsorbed NO, NO-,NO2-, and NO3-) present on the catalyst surface and revealed that O2 desorption occurs at the high temperature region together with the NO desorption as the product of NO2and/or NO3- decomposition. This region corresponds with the temperature of launching NO conversion curve, which together with the results from the transient state experiments proved that O2 desorption is the slowest step while the reaction steps including NOx-formation and those leading to N2 release are fast. The Langmuir-Hinshelwood mechanism was proposed as a plausible way of direct NO decomposition over K/ Co4MnAlOx catalysts and NO2- and NO3- were determine as the main reaction intermediates.