Dissociative adsorption of 2,3,7,8-TCDD on the surfaces of typical metal oxides: a first-principles density functional theory study

Abstract

The initial dissociative adsorption step of the 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) molecule on the surfaces of MgO, CaO, and CuO has been studied by density functional theory (DFT) using periodic slab models. It is found that the 2,3,7,8-TCDD molecule undergoes a similar dissociative adsorption step during the decomposition over the three metal oxide surfaces. The adsorption configuration of 2,3,7,8-TCDD first converts from a parallel mode into a vertical one, then a nucleophilic substitution process takes place, where the surface oxygen atom attacks the aromatic carbon to form a surface phenolate with the chlorine atom moving to the top of the nearest surface metal atom. The calculated apparent activation energy of the dissociation increases in the order of CuO < CaO < MgO. The reaction heat is -0.67 eV, -0.75 eV, and 0.45 eV for CuO, CaO, and MgO, respectively, suggesting the thermodynamic tendency of MgO < CuO < CaO, which parallels the trend of the nucleophilicity of surface oxygen atoms. This study suggests that metal oxides with more nucleophilic and less tightly-bonded surface oxygen atoms might be more promising for the decomposition of polychlorinated dibenzo-p-dioxins and dibenzofurans.

Theoretical Study on Catalytic Pyrolysis of Benzoic Acid as a Coal-Based Model Compound

“…The optimized parameters of bulk γ-Al 2 O 3 using the non-spinel model − were a = 5.595 Å, b = 8.425 Å, and c = 8.072 Å, which were consistent with the experimental values ( a = 5.587 Å, b = 8.413 Å, and c = 8.068 Å) . The cubic crystal structure was selected for CaO and MgO, with optimized parameters of 4.811 and 4.211 Å, respectively, which were also in accordance with the previous results. , …”

“…Previous studies showed that ZnO (101̅0), γ-Al 2 O 3 (110), CaO (100), and MgO (100) surfaces were the main surfaces of ZnO, γ-Al 2 O 3 , CaO, and MgO. ,− Therefore, these four surfaces were used in the paper, and the top views of the selected four surfaces were shown in Figure . ZnO (101̅0), γ-Al 2 O 3 (110), CaO (100), and MgO (100) surfaces were modeled using a p (3 × 3) super cell with six layers, p (1 × 2) super cell with four layers, p (3 × 4) super cell with four layers, and p (3 × 4) super cell with four layers.…”

Formation Mechanism of Environmentally Persistent Free Radicals on Alkaline Earth Oxide Surfaces

“…In this study, the (100) surface of AEMOs was selected as an ideal model because it is the most stable exposed surface among the various surfaces of AEMOs. , The p (2 × 2) slabs containing four atomic layers were employed. Moreover, the bottom atomic layer was fixed, while the top three atomic layers and the adsorbed species were allowed to relax.…”

Catalytic activity, water resistance and stability of hematite nanomaterials in oxidative removal of polychlorinated aromatic hydrocarbons can be simultaneously enhanced through facet engineering

“…The catalytic oxidation of o-DCB by α-Fe 2 O 3 likely started with the adsorption of o-DCB molecules on α-Fe 2 O 3 surfaces through the binding of Cl atoms to Lewis acid sites (mainly Fe 3+ atoms). 13,16,23,37 The electron-withdrawing effect of Lewis acids can weaken the C-Cl bond, which promotes the dechlorination reaction at low temperatures, 10,20,21 allowing the formation of C x H y O z intermediates and initiating their further oxidation. 22 Understandably, the greater abundance of Lewis acid sites of NR-{110} provided the material higher efficiency in binding and degrading o-DCB.…”