Liquid-phase carbon dioxide conversion catalyzed via copper-based metal-organic framework catalysts for formic acid synthesis

Abstract

In this study, a catalytic performance of a copper based metal-organic framework (Cu-BTC) acting as a pre-catalyst was systematically investigated for a liquid-phase carbon dioxide (CO2) conversion for formic acid (HCOOH) synthesis under mild conditions. Using sodium borohydride (NaBH4), system enabled efficient CO2 conversion without the need for elevated pressure, intensive energy input, or harsh reaction media. Post-reaction characterization confirmed an in-situ transformation of Cu-BTC into highly active Cu-Cu2O nanostructures, which served as an active catalyst. Comprehensive product analysis via gas and liquid chromotography (HPLC and GC-FID) corroborated that NaBH4 and Cu-BTC-derived copper species act cooperatively to drive selective formation of HCOOH. Catalytic tests were performed under 45 degrees C, 1 atm CO2, and pH 7 by using CO2 concentrations ranging from 20% to 100%, and recyclability test of the catalysts was investigated for 5 cycles. The liquid-phase CO2 conversion approach achieved simultaneous conversion (similar to 60%) and perfect selectivity (>99%). Notably, calcinated Cu-BTC (C-Cu-BTC) catalyst exhibited reusability with activity increasing after initial cycles due to structural evolution of active phase. Overall, this work highlighted the potential of Cu-BTC as a template for generating practical and scalable Cu-Cu2O catalysts for the liquid-phase CO2 conversion for high-purity HCOOH synthesis.