Density Functional Theory Study on the Effect of Sodium on the Adsorption of NO on a Char Surface

Abstract

In order to clarify the effect of sodium on the heterogeneous adsorption of NO on a char surface, several reasonably simplified saturated and unsaturated char models were selected as research objects, and Na atoms were decorated on the char models. Each char model and NO adsorption product were optimized by using density functional theory at the GGA-PBE (generalized gradient approximation-Perdew−Burke−Ernzerhof) level to obtain the adsorption energy of NO on different models. The results indicate that the addition of Na atoms catalyzes the adsorption of NO molecules by an saturated char structure, the adsorption form is changed from physisorption to chemisorption, and the adsorption energy is increased from −15.6 to −98.2 kJ/ mol. The adsorption energy of NO molecules with an unsaturated armchair-type char structure containing edge active sites is affected by sodium atoms, increasing from −211.7 to −303.6 kJ/mol, while the adsorption capacity of the zigzag-type char structure for NO molecules is hardly affected by Na atoms. This study provides a theoretical basis for the development of clean utilization technology of high-alkali coal.

Mechanism of the Heterogeneous Reduction of NO on a Sodium-Doped Char Surface: A First-Principles Study

“…Char Structure Doped with Sodium. The screening of the optimum adsorption sites for the sodium doped on different char surfaces has been completed in the previous work, 26 and it has been found that the structure of sodium doped at cavity sites is the most stable structure. The specific process of adsorption was not repeated in this paper, only the electronic properties of the models were analyzed in order to understand the reactivity of different models, and theoretical support was provided for the subsequent mechanism analysis.…”

“…Some studies , have shown that an aromatic cluster structure (with three to seven benzene rings) with irregular stacking comprises the coal char structure; in addition, the armchair structure and zigzag structure are the two main forms of coal char models. In this work, char structures of the armchair and zigzag models are adopted as the two prototypes, which have been approved by most researchers, similar to the previous research by the authors, as shown in Figure .…”

“…In this research, the computational methods are very similar to those in the previous studies . All the calculations were performed with the Dmol in the Materials Studio using the DFT. − The GGA (generalized gradient approximation)–PBE (Perdew–Burke–Ernzerhof method) functional was used to describe the electron exchange–correlation potential.…”

“…Overall, the heterogeneous reduction mechanism between NO and char is extremely complex, and a lot of work still remains. The authors 26 have investigated the effect of sodium on the adsorption of NO on the char surface based on the DFT method, and the results showed that the addition of sodium catalyzes the adsorption of NO molecules on the coal char structure. However, it was not studied well enough to understand the micromechanism of sodium on the facilitation of the heterogeneous reduction of NO.…”

DFT Study on the Effect of Na on NO Reduction with Nitrogen-Containing Char from Zhundong Coal

“…Liu et al declared that the addition of Ca and K greatly promoted the adsorption of NO on carbon. Yang et al , investigated the effect of Na on the adsorption and reduction of NO on char and found that sodium not only favored the adsorption of NO at the edge of the armchair model but also promoted the reduction process by lowering the reaction energy barrier and increasing the reaction rate. Therefore, the presence of alkali metals reduces activation energy of the heterogeneous reduction of NO with char and increases its reaction rate.…”