Charge effects on alkanes and the potential applications in selective catalysis: insights from theoretical studies

Abstract

Methane structures endowed with different charges have been experimentally observed, but understanding of them currently remains rather limited. With the aid of ab initio calculations, a systematic work was carried out on the methane structures with different charges as well as on the structures of the neutral methane molecule bound to anions (O^2 −  and F⁻ ) and cations (Na⁺ and Mg^2 + ). The geometry of the neutral methane species was found to be well reserved in the negatively charged structures but severely distorted in the positively charged ones. The binding modes of the neutral methane species with cations (Na⁺ and Mg^2 + ) and anions (O^2 −  and F⁻ ) are threefold and onefold, respectively. The smallest and largest elongations of the C–H bonds in methane were observed in the binding with Na⁺ and O^2 − , respectively. According to the C–H bond dissociation energies (BDE1s), the dissociation pathways were determined for all the structures, and are in agreement with the experimental data. It was further revealed that the first C–H BDE1s are heavily dependent on the charges of the methane species. Through the charge effects, the activations of the first C–H bonds in methane become facile; in addition, the selective activations and conversions can be fine-tuned as well. Accordingly, the charge effects have the potential to be employed in the effective utilisation of alkanes.

Keywords:

• ab initio calculations
• alkanes
• charge effects
• C–H bonds
• selective activations

Acknowledgements

This work was financially supported by the Ministry of Science and Technology of China (No. 2005CB221405), Major State Basic Research Development Programs (No. 2004CB719902) and National Natural Science Foundation (No. 20633060).