Regulating electronic environment on alkali metal-doped Cu@NS-SiO2 for selective anisole hydrodeoxygenation

Abstract

Lignin utilization is a potential approach for replacing fossil energy and releasing the environment pressure. Herein, we synthesized a series of novel Cu-based catalysts, Cu@NS-SiO₂ (NS = nano sphere) and alkali metals (Na, K, Rb, and Cs) doped Cu@NS-SiO₂, and applied them in hydrodeoxygenation reaction of anisole. High Cu dispersion was presented on all catalysts. The modification of alkali metals on Cu@NS-SiO₂ significantly enhanced the electron density of Cu sites in the following order: Cs > Rb > K > Na, among which Cs decreased the Cu 2p_3/2 binding energy most (by 0.7 eV). Moreover, the modification did not substantially affect the geometric structure of Cu species. This regulable electronic environment of Cu sites was crucial for selective deoxygenation and inhibiting the hydrogenation of aromatic rings in anisole, and thus promoted the selectivity of benzene. Compared with Cu@NS-SiO₂ (∼59%), the highest benzene selectivity was obtained on Cs/10Cu@NS-SiO₂ at ∼83%.