Density functional theory study on the reaction mechanism of selective catalytic reduction of NO by NH3 over the γ-Fe2O3 (0 0 1) surface

Synthesis of Disubstituted Carboxonium Derivatives of Closo-Decaborate Anion [2,6-B10H8O2CC6H5]-: Theoretical and Experimental Study

A comprehensive study focused on the preparation of disubstituted carboxonium derivatives of closo-decaborate anion [2,6-B10H8O2CC6H5]- was carried out. The proposed synthesis of the target product was based on the interaction between the anion [B10H11]- and benzoic acid C6H5COOH. It was shown that the formation of this product proceeds stepwise through the formation of a mono-substituted product [B10H9OC(OH)C6H5]-. In addition, an alternative one-step approach for obtaining the target derivative is postulated. The structure of tetrabutylammonium salts of carboxonium derivative ((C4H9)4N)[2,6-B10H8O2CC6H5] was established with the help of X-ray structure analysis. The reaction pathway for the formation of [2,6-B10H8O2CC6H5]- was investigated with the help of density functional theory (DFT) calculations. This process has an electrophile induced nucleophilic substitution (EINS) mechanism, and intermediate anionic species play a key role. Such intermediates have a structure in which one boron atom coordinates two hydrogen atoms. The regioselectivity for the process of formation for the 2,6-isomer was also proved by theoretical calculations. Generally, in the experimental part, the simple and available approach for producing disubstituted carboxonium derivative was introduced, and the mechanism of this process was investigated with the help of theoretical calculations. The proposed approach can be applicable for the preparation of a wide range of disubstituted derivatives of closo-borate anions.

Calcium poisoning mechanism on the selective catalytic reduction of NOx by ammonia over the γ-Fe2O3 (001) surface

γ-Fe₂O₃ has an excellent low-temperature selective catalytic reduction (SCR) deNO_x performance, but its resistance to alkaline earth metal calcium (Ca) is poor. In particular, the detailed mechanism of Ca poisoning on the γ-Fe₂O₃ catalyst at the atomic level is not clear. Hence, the density functional theory method was used in this research to investigate the influence mechanism of Ca poisoning on the NH₃-SCR over the γ-Fe₂O₃ catalyst surface. The findings reveal that NH₃, NO, and O₂ molecules can bind to the γ-Fe₂O₃ (001) surface to generate coordinated ammonia, monodentate nitroso, and adsorption oxygen species, respectively. The main active site is Fe₁-top. For the γ-Fe₂O₃ with Ca poisoning, the Ca atom has a high adsorption energy on the surface of γ-Fe₂O₃ (001), which covers the catalyst surface and reduces the active sites. The presence of Ca atom decreases the adsorption performance of NH₃, while slightly improving the NO and O₂ adsorption. In particular, the Ca atom restrains the NH₃ activation and NH₂ formation, which is detrimental to the NH₃-SCR process.

Effect of doping Cr on NH3 adsorption and NO oxidation over the FexOy/AC surface: A DFT-D study

Activated carbon supported iron-based catalysts (Fe_xO_y/AC) show good deNO_x efficiency at low temperature. The doping of chromium (Cr) greatly improves the catalyst activity. However, the detailed effect of doping Cr over Fe_xO_y/AC surface at molecular level is still a grey area. In this study, the roles of Cr dopant on gas adsorption and NO oxidation were deeply investigated by a DFT-D3 method. Results show that the synergy of Cr-Fe bimetal improves the binding capacity of Fe₂O₃/AC and Fe₃O₄/AC surfaces after doping Cr. NH₃ can be adsorbed on Cr and Fe sites to form coordinated NH₃. Doping Cr greatly improves the NH₃ adsorption property on the Fe₃O₄/AC surface. NO molecule can combine with Cr, Fe, and O sites to form nitrosyl and nitrite. The doping of Cr increases the adsorption performance of NO on the Fe₂O₃/AC and Fe₃O₄/AC surfaces, especially for Fe₃O₄/AC surface. Furthermore, NO can be oxidized to NO₂ by adsorption oxygen or active O sites of Fe_xO_y clusters. The doping of Cr restrains the formation of insoluble chelating bidentate nitrates and greatly reduces the reaction energy barrier of NO oxidation on the Fe_xO_y/AC surface, which can promote the deNO_x reaction.

A DFT-D study on the reaction mechanism of selective catalytic reduction of NO by NH3 over the Fe2O3/Ni(111) surface

The adsorption and SCR reaction mechanism of NH₃, NO, and O₂ molecules on the Fe₂O₃/Ni(111) catalyst surface was revealed.

Adsorption mechanism of NH3, NO, and O2 molecules over the FexOy/AC catalyst surface: a DFT-D3 study

The surface model of the Fe_xO_y/AC catalyst was constructed and the adsorption mechanism of gas molecules on its surface was revealed.