Japanese researchers produce formic acid from CO2

In Japan, photoreduction of CO2 into transportable fuel like formic acid (HCOOH) is a great way of dealing with CO2’s rising levels in the atmosphere. To aid in this mission, a research team from Tokyo Tech chose an easily available iron-based mineral and loaded it onto an alumina support to develop a catalyst that can efficiently convert CO2 into HCOOH with ~90% selectivity.

To turn this lucrative solution into reality, scientists developed photocatalytic systems that could reduce CO2 with the aid of sunlight. Such a system consists of a light-absorbing substrate (i.e., a photosensitizer) and a catalyst that can enable the multi-electron transfers required to reduce CO2 into HCOOH. And thus began the search for a suitable and efficient catalyst!

Solid catalysts were deemed the best candidates for this task, due to their efficiency and potential recyclability, and over the years, catalytic abilities of many cobalt, manganese, nickel, and iron-based metal-organic frameworks (MOFs) have been explored, with the latter having some advantages over other metals. However, most of the iron-based catalysts reported thus far only yield carbon monoxide as the main product, instead of HCOOH.

The team adopted a simple impregnation method to synthesize their catalyst. They then used the iron-loaded Al2O3 material for photocatalytic reduction of CO2 at room temperature in the presence of a ruthenium-based (Ru) photosensitizer, an electron donor, and visible light of wavelength over 400 nanometer. 

The results were quite encouraging; their system showed 80-90% selectivity towards the main product, HCOOH, and a quantum yield of 4.3% (which indicates the system’s efficiency).

This study presents a first-of-its-kind, iron-based solid catalyst that can generate HCOOH when accompanied by an effective photosensitizer. It also explores the importance of a proper support material (Al2O3) and its effect on the photochemical reduction reaction. 

The insights from this research could aid in the development of new catalysts—free of precious metals—for the photoreduction of CO2 into other useful chemicals.