The mechanism of copper-catalyzed decomposition of ethyl methyl ether: a DFT study
Xiaoli Zhang, Jinyu Tan, Shiling Wei, Jiuzheng Yin, Lidong Zhang, Lixia Wei
Abstract
Ether-based lubricating oils have attracted widespread attention due to their exceptional performance. However, nascent metal surfaces generated during friction may act as catalysts, hence accelerating lubricant degradation. In this study, ethyl methyl ether (CH<sub>3</sub>CH<sub>2</sub>OCH<sub>3</sub>, EME) was selected as a model compound to investigate the catalytic effect of copper on the degradation of ether-based lubricants. Density functional theory (DFT) calculations were performed to study the decomposition of EME on the Cu(111) surface. The results indicate that C–H bond cleavage has the lowest energy barrier, followed by C–O bond cleavage, while C–C bond cleavage has the highest energy barrier. Kinetic analyses reveal that the primary decomposition pathway of EME is as follows: EME* → CH<sub>2</sub>CH<sub>2</sub>OCH<sub>3</sub>(I)* → C<sub>2</sub>H<sub>4</sub>* + CH<sub>3</sub>O*. Initially, EME undergoes dehydrogenation on the Cu(111) surface, overcoming an energy barrier of 1.34 eV to form CH<sub>2</sub>CH<sub>2</sub>OCH<sub>3</sub>(I)*. This is the rate-determining step for the decomposition of EME*. Subsequently, CH<sub>2</sub>CH<sub>2</sub>OCH<sub>3</sub>(I)* breaks down into ethylene and methoxyl with an energy barrier of 0.65 eV, leading to the destruction of the ether functional group. Since the oxygen atom serves as the adsorption center for ether-based lubricants, the stability of an ether is expected to improve, possibly by substituting hydrogen atoms near oxygen with fluorine atoms.