Subsurface Li Monolayer on Cu(111) Surfaces for Upgrading Ethanol to n-Butanol: A Computational Study

Abstract

Butanol is a highly desirable fuel and fuel additive due to its closely related physical properties to gasoline. The Guerbet upgrade of ethanol to n-butanol is one of the most important processes in a bio-refinery. Herein, density functional theory (DFT) calculations are employed to examine the upgrading of ethanol to n-butanol over the periodic Cu(111) and alkali metal (Li and Na)-incorporated periodic Cu(111) surface nanocatalysts. The Li-subsurface Cu(111) structure [Li@Cu(111)] is found to be the most stable structure among the considered catalysts, and thus the Li@Cu(111) structure is considered for the mechanistic investigation of upgrading of ethanol to n-butanol. All the possible mechanistic pathways have been probed, and the most plausible reaction mechanism has been determined. The predicted excellent activity can be attributed to the significant charge transfer from the Li to the Cu surface, which in turn improves the adsorption of important intermediates through an oxygen atom. This study contributes to the rational design of high-performance metal catalysts and clearly explains the importance of subsurface chemistry in heterogeneous catalysis.