Oxygen effect in NO direct decomposition over K/Co-Mg-Mn-Al mixed oxide catalyst–Temperature programmed desorption study

Surface Potassium Promotion of Co4MnAlOx in Direct NO Decomposition Generates the Same Type of Active Sites as Bulk Promotion

“…It is obvious that N 2 desorption takes place in the whole temperature range. The desorbed amount is very small, but it is necessary to take it into account, whereas there was no N 2 desorption observed during TPD-NO measurements in our previous studies , over BP samples.…”

“…In our previous studies, , several overlapping desorption peaks were identified in TPD-NO curves for the K/Co 4 MnAlO x catalyst prepared by the BP method . According to the literature, , the first desorption peak ( T ≈ 150 °C) can be assigned to mononitrosyl species loosely bound on Me 3+ in octahedral positions, the second desorption peak ( T ≈ 200–300 °C) to dinitrosyl species bound on Me 2+ in tetrahedral positions, and the third desorption peak ( T ≈ 300–400 °C) to mononitrosyl adspecies bound on tetrahedral Me 2+ . The desorption peak at temperatures above 500 °C was assigned to the surface nitrates.…”

“…The deconvoluted desorption curves of O 2 desorbed from the tested catalysts during TPD-NO are depicted in the right column of Figure . Oxygen starts to desorb from the surface at temperatures >450 °C, which indicates that oxygen is strongly bound on the catalyst. , It is noteworthy that the O 2 desorption curves for samples K4_carb, K4_ac, and K0 are composed of three overlapping peaks; on the other hand, those for samples K4_nit and K4_ox are composed of two peaks. The third desorption peak could be associated with the lattice oxygen since K4_carb, K4_ac, and K0 contain higher amounts of lattice O than the other samples (Table S5).…”

“…At the beginning, the adsorption of gaseous NO on transition metals takes place, leading to the formation of NO – , which reacts with lattice or surface oxygen, forming NO 2 – species. At the temperatures above 600 °C, the nitrite species are decomposed to nitrogen and oxygen. ,, In our previous works, , N 2 desorption was evaluated as a fast step, whereas no N 2 was detected during TPD-NO measurements, and increase of N 2 signal in transient kinetic analysis was fast after NO switch on. In the case of samples studied in this work, N 2 appears during TPD-NO, and the delay in N 2 signal during transient kinetic analysis is bigger.…”

“…In our previous studies, − Co–Mn–Al mixed oxides promoted by potassium showed an interesting activity level in the direct NO decomposition reaction. The presence of potassium was shown to be the key factor for the catalytic activity. ,, It is believed that the addition of potassium facilitates desorption of chemisorbed oxygen by weakening the metal–oxygen bond , and allows the formation of reactive nitrite surface intermediates. , Potassium is known for its low ionization potential, thanks to which it can influence the electron density and also basicity of oxygen anions in its coordination sphere, which is in turn reflected in the decrease of the cobalt and manganese electron density due to the formation of the surface dipoles. − …”