Lithium iodide promoted CO2 hydrogenation towards ethanol via biphasic lewis-acid-base pairs synergistic catalysis

Abstract

Ethanol synthesis via CO₂ hydrogenation is of great importance in view of its high-value utilization. Herein, combining with heterogeneous and homogenous catalysis, we have developed an efficient biphasic Lewis-acid-base pairs synergistic catalysis strategy from CO₂ hydrogenation. Apart from conventional heterogeneous ethanol synthesis route, it was surprisingly found that LiI homogenous promoter significantly enhanced CO₂ conversion, ethanol selectivity, and productivity. LiI promoted CO₂ dissolution in pure water and accelerated reaction intermediates consumption, favoring CO₂ conversion. In detail, it can weaken C-O bond of CH₃OH intermediate through Li⁺-I^- Lewis-acid-base catalysis. The formed CH₃I* with lower bond energy for C-I was more facile to dissociate into CH₃*, favoring its subsequent coupling with CO* to form ethanol. In combination of Rh₁/CeTiO_x catalyst, LiI promoter, and methanol as solvent, a record-breaking ethanol yield was achieved (223.1 mmol·g⁻¹·h⁻¹). The obtained ethanol yield was about 18.7 times of that reported the best result in literatures. Especially, the established catalyst system could also be applied for synthesis of higher-carbon-number alcohols by the CO₂ hydrogenation with other alcohols solvent (C_nH_2n+1OH, n = 2,3…).