The Dissociation Of CO₂ On La₂O₃ (001) Surface

Carbon dioxide reforming of methane to produce synthesis gas is of great significance in alleviating the energy crisis, reducing greenhouse gas emissions and improving human's living environment. However, the industrialization process is hinder because of coke produced in the process which affects the activity and stability of catalyst. It has been found that, in experiment, La2O3 can catalyze the dissociation of CO2, and oxygen species produced by CO2 dissociation are the key species for carbon delimination.Based on density functional theory in the generalized gradient approximation, together with periodic slab model, the dissociation of the CO2 on the surface of La2O3 has been performed, and the migration processes of oxygen species and carbon species have been examined in this work.The results show that it needs to overcome a barrier of 378.4 kJ·mol-1 that CO2 dissociates into CO and O atoms directly (CO2*→O*+CO), while the activation energy is 138.1 kJ·mol-1 in the H-assisted dissociation path CO2+H→COOH→OH+CO on the perfect surface of La2O3 (001). However, it has a lower activation energy of 68.7 kJ·mol-1 for CO2 dissociation on the defective La2O3 (001) surface [CO2*+Ov-Surf.→CO+Surf. (Ov-Surf for oxygen vacancy on La2O3 surface, Surf. for perfect surface)]. From the results, one can conclude that it is easy for CO2 to dissociate on the surface with H preadsorbed and on the defective surface. This may be the reason that carbon deposition can be eliminated on La2O3 surface.The migrations of the O, OH, and C species have also been investigated on the perfect La2O3 (001) surface. The calculated activation energies of the migration for O, OH and C are 144.8 kJ·mol-1,29.4 kJ·mol-1 and 239.4 kJ·mol-1, respectively. Obviously, the active energies for migration of 0 and OH are lower than that of C, which means that the oxygen species is easy to migrate and react with C resulting in carbon elimination. On the other hand, the active energy for migration of C is higher, which indicates it is difficult to move and accumulate to yield carbon deposition.