Benzoic acid (C 6 H 5 COOH) is selected as a coal-based model compound, and its catalytic pyrolysis mechanisms on ZnO, γ-Al 2 O 3 , CaO, and MgO catalysts are studied using density functional theory (DFT) compared to the non-catalytic pyrolysis mechanism. DFT calculation shows that the pyrolysis process of C 6 H 5 COOH in the gas phase occurs via the direct decarboxylation pathway (C 6 H 5 COOH → C 6 H 6 + CO 2 ) or the stepwise decarboxylation pathway (C 6 H 5 COOH → C 6 H 6 COO → C 6 H 6 + CO 2 ). For C 6 H 5 COOH catalytic pyrolysis on the ZnO (101̅ 0) surface, the preferred reaction pathway is C 6 H 5 COOH → C 6 H 5 COO + H → C 6 H 6 + CO 2 , whereas the preferred reaction pathway on γ-Al 2 O 3 (110), CaO (100), and MgO (100) surfaces is C 6 H 5 COOH → C 6 H 5 COO + H → C 6 H 5 + CO 2 + H → C 6 H 6 + CO 2 , indicating that the presence of catalysts changed the pyrolysis mechanism of C 6 H 5 COOH. In addition, dissociative adsorption of C 6 H 5 COOH is observed on these surfaces. It is found that ZnO (101̅ 0), MgO (100), and CaO (100) are beneficial to C 6 H 5 COOH decomposition, but γ-Al 2 O 3 (110) is disadvantageous to the C 6 H 5 COOH decomposition. At the same reaction temperature, the rate constants show the order: k(ZnO) > k(MgO) > k(CaO) > k(no catalyst) > k(γ-Al 2 O 3 ).

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The sulfurized processes of H 2 S on dehydrated (100) and (110) as well as partially hydrated (110) surfaces of g-Al 2 O 3 were investigated using a periodic density functional theory method. The adsorption configurations of possible intermediates and the potential energy profiles of reaction are depicted. Our results show that H 2 S adsorbs preferentially on the Al site along with the S bond, and the adsorption energies are À32.52 and À114.38 kJ mol À1 on the dehydrated (100) and (110) surfaces, respectively. As the reaction temperature of the desulfurization changes, the (110) surface presents different levels of hydroxyl coverage, which affects the adsorption structures of species and reaction energies of dissociation processes. The bonding strengths of H 2 S on the partially hydrated (110) surfaces are weaker than on the dehydrated (110) surface. Compared with the 3.0 and 8.9 OH per nm 2 surfaces, the H 2 S has the weakest adsorption energy (À39.85 kJ mol À1 ) and the highest activation energy (92.06 kJ mol À1 ) on the 5.9 OH per nm 2 surface. On the 8.9 OH per nm 2 surface, the activation energy of the second dissociation step (rate-determining step) for H 2 S dissociation is merely 38.32 kJ mol À1 . On these involved surfaces, cleavage processes of the two H-S bonds present facile activation energies, which are facilitative to desulfurization. View Article Onlinea Param: parameters. b D100, the dehydrated g-Al 2 O 3 (100) surface. c D110, the dehydrated g-Al 2 O 3 (110) surface. d FS denotes the nal state. e 3.0 OH per nm 2 , 5.9 OH per nm 2 and 8.9 OH per nm 2 represent the different levels of hydroxyl coverage for g-Al 2 O 3 (110) surface. This journal isFig. 6 Calculated probable potential energy profiles for dissociation of H 2 S (a) and HS (b) on dehydrated and partially hydrated g-Al 2 O 3 surfaces. (D100 surface, the dehydrated g-Al 2 O 3 (100) surface; D110 surface, the dehydrated g-Al 2 O 3 (110) surface).This journal is