Abstract
To address the mechanism of C-C bond cleavage on the metal surface of the M/SiO2 (M represents metal) catalyst is desirable and vital during the catalytic depolymerization process of lignin in solvents. Density functional theory simulation is used to determine the energy of C-C bond dissociation, adsorption geometry, adsorption energy and electronic structures of three kinds of the beta-1 bond contained lignin model compounds (Mo1, Mo2 and Mo3), which were adsorbed on the (100) surface of metal (Ni, Cu, W) in the catalysts. The bond dissociation energy (BDE) of C-alpha-C-beta was found to be lower than those of C-aryl-C-alpha and C beta-C-aryl bond. The C-alpha-C-beta in Mo2 was adsorbed via a p configuration on the Ni(100) and Cu(100) surfaces, exhibiting the weak dissociation bond energy. The -OH group was anchored as eta(1)(O) configuration which was instable on the (100) surface of W. The model compounds might be co-adsorbed with hydrogen on the metal surface under the reaction condition. The adsorption of Mo2 on the (100) surface of Cu was changed to the eta(1)(O) pattern, while the C-alpha-C-beta BDE was declined on the (100) surface of Ni and Cu involving the coverage of hydrogen. The adsorption on W(100) had no effect on the decline of C-alpha-C beta BDE. The adsorption of Mo2 on the (100) surface of metals plays different roles on weakening the C-alpha-C beta BDE, giving conceptual guide for the selective depolymerization of lignin to specific chemicals.