Article pubs.acs.org/JPCC
Methane Activations by Lanthanum Oxide Clusters Yang Lei, Changqing Chu, Shenggang Li,* and Yuhan Sun CAS Key Laboratory of Low-Carbon Conversion Science and Engineering, Shanghai Advanced Research Institute, Chinese Academy of Sciences, 100 Haike Road, Shanghai 201210, China S Supporting Information *
ABSTRACT: Density functional theory and coupled cluster theory were employed to study the activations of CH4 by neutral lanthanum oxide clusters (LaO(OH), La2O3, La3O4(OH), La4O6, La6O9) as models for the La2O3 catalysts for the oxidative coupling of methane (OCM) reaction. The physisorption energies (ΔH298 K) of CH4 on the lanthanum oxide clusters were predicted to be −4 to −3 kcal/mol at the CCSD(T) level. CH4 is activated by hydrogen transfer to one of the O sites on the lanthanum oxide clusters, and the energy barriers (ΔE0 K) from the physisorption structures were calculated to be modest at ∼20 kcal/mol for La2O3 and ∼25 kcal/mol for the other clusters. This is accompanied by the formation of a La−CH3 bond, whose bond dissociation energy (ΔE0 K) was calculated to be 53 to 60 kcal/mol. CH4 chemisorption is slightly exothermic on LaO(OH) and La2O3, whereas it becomes increasingly endothermic for the larger lanthanum oxide clusters. The formation of the CH3 radical was predicted to be substantially endothermic, by ∼50 kcal/mol for LaO(OH) and La2O3 and 64 to 76 kcal/mol for La3O4(OH) and La4O6 (ΔH298 K). Calculations on the activation of CH4 by La6O9 with a higher coordination number for both the La and O sites than La4O6 yield an energy barrier slightly higher by
