Promoting Effects of Na and Fe Impurities on the Catalytic Activity of CaO in the Reduction of NO by CO and H₂

Abstract

The heterogeneous reduction of NO by H2 and CO over different CaO materials is investigated. The dependence of the specific NO reduction rate on the impurity content is demonstrated for both reducing species. The roles of two specific impurities, i.e., Na and Fe, as well as their combined effect are investigated. The apparent activation energies for the NO + CO and NO + H2 reactions are determined for three different calcium oxides. Values between 26 and 28 kcal/mol are obtained. The influence of impurity content is found in the preexponential factor of the Arrhenius equation. A reaction mechanism based on a rate-determining surface-oxygen-abstraction step is suggested. This mechanistic understanding is explored to compare the activities of other alkaline-earth oxides. Particularly, a linear correlation between the apparent activation energy and the lattice parameter is observed.

Amorphous Li-Al-Based Compounds: A Novel Approach for Designing High Performance Electrode Materials for Li-Ion Batteries

“…However, the presence of Fe or Fe-oxides influences the lithiation process positively, since powder P1 achieves enlarged specific capacities compared to P2. Similar promoting effects of Fe or Fe compounds are well documented in disciplines beside battery or electrochemical research such as heterogeneous catalysis [30,31]. Figures 8c,d show the development of the specific capacities after each cycle at a C-rate of C/50 calculated for different active masses.…”

Effects of O2 on the Reduction of NO over Prereduced CaO Surfaces: A Mechanistic Understanding

“…Still, common properties are sought by focusing on the necessary prerequisites for the reduction of NO. This article is part of a series that tries to elucidate the nitrogen chemistry during reduction of NO over alkaline earth oxide surfaces. − CaO is used as a model substrate to study basic reactions, both by experiment 11-13 and theory. − In a previous work, correlation was demonstrated between catalytic activity toward the reduction of NO by CO or H 2 , and the impurity content (Na and Fe) of the CaO material . The role of the impurities is to provide electron sinks during the surface oxygen abstraction by the reducing agent.…”

“…Two models describing this step are currently under debate, i.e., a semiconductor model based on O - states in the band gap , and a model based on F-centers , and a mechanism involving an N 2 O 2 n - intermediate was suggested. , Furthermore, the effect of the oxygen abstraction step on the subsequent reduction of NO was shown to be independent of the reducing agent, i.e., H 2 or CO .…”

Valence structure of alkaline and post-transition metal oxides

“…[1][2][3][4][5][6][7][8] Two classes of oxides; the alkaline oxides AeO (Ae = Be, Mg, Ca, Sr, Ba) and post-transition metal oxides MeO (Me = Zn, Cd, Hg) are of note since in the "complete oxidation" regime they only contribute s electrons to the valence structure. The lack of d electrons in the former class, and the presence of a completely filled valence d shell in the latter class suggests that their electronic structure may be accurately calculated using weakly correlated methods.…”

“…They are used in a wide range of industrial applications from catalysis to microelectronics. 1,2 The post transition metal oxides are II-VI type semiconductors, and are used in a variety of electronic applications. The most interesting of these is ZnO, which has been the subject of research in optical and photo-electronic 9-11 and as a host material for dilute magnetic semiconductors [12][13][14] for quite some time.…”