The greenhouse effect is a phenomenon that causes harmful global environmental changes due to increasing CO₂ levels in the earth’s atmosphere. As such, reducing the levels of CO₂ through means of capturing the CO₂ is a potential solution to mediate the greenhouse effect. Currently, porous or mesoporous absorbents are utilized to capture CO₂. However, upscaling this process is often impractical due to the costly CO₂ storage and transportation. Thus, researchers at VCU have developed an effective alternative to reducing atmospheric CO₂ levels by capturing and converting it into useful bi-products, such as formic acid, via novel ligated metal chalcogenide clusters.

The technology

Converting CO₂ to formic acid without an effective catalyst is challenging as CO₂ is inherently inert.  The use of VCU’s novel metal chalcogenide cluster as a catalyst for CO₂ hydrogenation contains a unique capability to alter its energy demand based on the attached ligand (i.e., the barrier height can be controlled by varying the number/type of attached ligands) (Figure 1 and Figure 2). For example, the un-ligated metal chalcogenide cluster produced significantly low barrier heights ranging from 0.3-0.4 electron volts (eV) compared to conventional catalysts. By selectively controlling the ratio of attached acceptor and donor ligands to the metal chalcogenide cluster, one can adjust the barrier heights for CO₂ hydrogenation in a stepwise manner. For instance, by attaching only three specific ligands to the cluster, one of the CO₂ hydrogenation barriers can be reduced to as low as 0.12 eV that will allow rapid thermochemical conversion of CO₂.

Figure 1. CO₂  =>HCOOH reaction pathway on [Ti₆Se₈(PMe₃)₃] metal chalcogenide cluster.

Figure 2. The relative trend of barrier heights for both hydrogenation steps on four ligated clusters.