Production of Formic Acid via Hydrogenation of CO₂ over a Copper-Alkoxide-Functionalized MOF: A Mechanistic Study

Abstract

Conversion of greenhouse gases to more valuable chemicals is important from both the environmental and industrial points of view. Herein, the reaction mechanisms of the hydrogenation of carbon dioxide (CO2) to formic acid (HCOOH) over Cu-alkoxide-functionalized metal organic framework (MOF) have been investigated by means of calculations with the M06-L density functional. The reaction can proceed via two different pathways, namely, concerted and stepwise mechanisms. In the concerted mechanism, the hydrogenation of CO2 to formic acid occurs in a single step. It requires a high activation energy of 67.2 kcal/mol. For the stepwise mechanism, the reaction begins with the hydrogen atom abstraction by CO2 to form a formate intermediate. The intermediate then takes another hydrogen atom to form formic acid. The activation energies are calculated to be 24.2 and 18.3 kcal/mol for the first and second steps, respectively. Because of the smaller activation barriers associated with this pathway, it therefore seems to be more favored than the concerted one. The catalytic effect of Cu-MOF-5 is also highlighted by comparing it with the gas-phase uncatalyzed reaction in which the reaction takes place in one step with a barrier of 73.0 kcal/mol. This study also demonstrates that the metal-functionalized MOF can be utilized for the greenhouse gas catalysis in addition to using it to capture and activate CO2.

Synthesis and Functionalization of Oriented Metal–Organic‐Framework Nanosheets: Toward a Series of 2D Catalysts

“…[ 58 ] In another report, the conversion of CO 2 to formic acid was performed on Cu-alkoxide-functionalized MOF-5 (Cu-MOF-5) in which the MOF-5 linkers were fi rst modifi ed with hydroxyl groups; then, www.afm-journal.de www.MaterialsViews.com the protons of the hydroxyl group were exchanged by copper cations via solution methods. [ 59 ] In contrast, our supported 2D copper catalysts can be obtained facilely from direct reduction of Cu(HBTC)-1 nanosheets in one single step, and the size of copper is adjustable depending on simple process conditions.…”

Metal‐Organic Framework‐Based Nanomaterials for Electrocatalysis

“…A modified Cu-alkoxide-functionalized MOF-5 module was established for the mechanism study of the hydrogenation process of CO 2 into HCOOH by DFT calculation. [122] Molecular simulation revealed two possible reacting routes, namely, the concerted and stepwise mechanisms, respectively. In the former one, hydrogenation took place in a single step with high activation energy of 67.2 kcal mol −1 , whereas in the latter one, CO 2 firstly formed formic intermediate with the adsorbed hydrogen atom abstraction and then took another hydrogen atom to give the formic acid.…”

Rational Design of Catalytic Centers in Crystalline Frameworks

“…For example, the reaction mechanism of the hydrogenation of CO 2 to HCOOH over Cu‐alkoxide‐functionalized MOF‐5 was investigated by DFT calculation with the M06‐L functional. It was shown that the reaction can proceed via two different pathways, namely, concerted and stepwise mechanisms . In the concerted mechanism, CO 2 is one‐step hydrogenated to generate HCOOH with a large activation barrier of 67.2 kcal mol −1 .…”