Remarkably boosting ethanol upgrading to higher alcohols through cooperative catalysis of surface-interface multiple-active sites on nitrogen-doped carbon decorated copper-based catalysts

Abstract

Upgrading biomass-derived ethanol to higher alcohols is a significantly promising process involving multi-step tandem reactions finely regulated by multiple active sites. However, the role of multiple active sites in addressing activity and selectivity toward alcohols still remains unclear. Herein, we developed supported copper catalysts decorated with surface trace-level nitrogen-doped carbon (NC) derived from melamine/Cu-Mg-Al layered double hydroxide composite precursors and studied their catalytic performance for converting ethanol to higher alcohols. As-constructed NC-decorated Cu-based catalyst, which was obtained by calcination of the precursor with a melamine/Cu molar ratio of 2:1 at 550 °C, achieved an 82% selectivity to higher alcohols at 63% ethanol conversion under reaction conditions (250 °C, 2 MPa pressure), along with unprecedentedly high ethanol conversion rate of 38.9 mmol·gcat−1·h−1 and production rate of higher alcohols (31.9 mmol·gcat−1·h−1), which are the highest standard among previously reported catalysts to date. By performing comprehensive structural characterizations and density functional theory calculations, it was revealed that surface modification of NC component promoted the dispersion of Cu particles and modulated the electronic structures of Cu species, facilitating the formation of Cu+ sites at metal-support interfaces and surface oxygen vacancies. Moreover, the significantly enhanced catalytic efficiency of Cu catalysts was mainly attributed to the favorable cooperative catalysis of multiple surface-interface active sites (Cu0, Cu+, oxygen vacancies, and acid-base sites), thereby accelerating tandem processes to produce higher alcohols during ethanol conversion. The present findings afford a new strategy for the rational design of high-performance supported copper catalysts for biomass-derived ethanol coupling to higher alcohols.