Artificial Chlorophyll-like Structure for Photocatalytic CO2 Chemical Fixation

Abstract:

Recently, Professors Yi Xie and Xiaodong Zhang's team from the University of Science and Technology of China, in collaboration with Professor Shuhu Liu from the Institute of High Energy Physics, Chinese Academy of Sciences, reported a porous nitrogen-doped carbon-based single-atom catalytic material with highly concentrated chlorophyll-like magnesium porphyrin Mg-N₄ active centers. Utilizing phenanthroline as the chelating ligand for Mg, a simple and efficient preparation of the chlorophyll-like magnesium porphyrin Mg-N₄ coordinated catalyst Mg-NC was achieved through a stepwise thermal decomposition calcination method. The synthesized Mg-NC exhibited excellent adsorption and activation capability towards epoxide substrates and demonstrated outstanding charge separation ability under photoexcitation conditions. By employing various modern physics (in-situ) characterization techniques combined with theoretical calculations, the in-depth reaction mechanism during the preparation of high-value cyclic carbonates through photocatalytic CO₂ chemical fixation was revealed. This work provides new insights into the design and construction of biomimetic enzyme heterogeneous photocatalysts and offers new understandings for developing photocatalytic CO₂ cycloaddition technologies with high catalytic activity.

Background:

Utilizing excess CO₂ emissions to produce high-value carbon-containing compounds presents a green and feasible solution for achieving the "dual carbon" pathway, which has attracted widespread attention from researchers in recent years. Among various reaction pathways, the synthesis of cyclic carbonates via the reaction of CO₂ with epoxides presents great potential for producing industrially valuable and widely applicable compounds. Cyclic carbonates, as environmentally friendly chemicals, are widely used as raw materials for methylation and carbonylation reactions, important monomers for preparing polyester materials, and electrolytes in high-performance batteries. However, traditional industrial synthesis often requires relatively harsh reaction conditions (high temperature, high pressure), which do not align with the industrial production goals of green chemistry. Therefore, the development of suitable photocatalysts to achieve the synthesis of cyclic carbonates under mild conditions is highly attractive.

Highlights:

In this work, the authors first predicted the stability and feasibility of the Mg-N₄ coordination structure based on density functional theory in nitrogen-doped graphite carriers (Figure 1).

Based on theoretical predictions, using phenanthroline as the chelating ligand for Mg, the authors successfully synthesized the chlorophyll-like magnesium porphyrin Mg-N₄ coordinated catalyst Mg-NC through a stepwise thermal decomposition calcination method (Figure 2a). XPS, aberration-corrected HADDF, and XANES confirmed that Mg was dispersed in a single-atom form throughout the material surface with unsaturated coordination structure of Mg-N₄ resembling chlorophyll (Figure 2b-j).

To validate the photocatalytic CO₂ conversion performance of the designed Mg-NC material, its catalytic activity and cycling stability were evaluated using the reaction of CO₂ with epoxides to synthesize cyclic carbonates as a probe reaction (Figure 3). The catalytic results showed that under similar reaction conditions, Mg-NC exhibited significantly higher catalytic activity than other heterogeneous photocatalysts. Under a light power density of 200 mW·cm², the photocatalytic epoxide conversion rate reached 9.67 mmol·g^-1·h^-1 (yield ~99%, selectivity 100%), demonstrating good cycling stability and substrate expandability.

In-situ ESR test results indicated that light mainly promoted the electron transfer from the Mg active center to the epoxide, weakening the C-O bond and facilitating its ring-opening and subsequent reaction processes (Figure 4a-c). DFT theoretical calculations of the complete reaction pathway for CO₂ cycloaddition revealed that epoxide ring-opening is the rate-determining step of the entire reaction process (Figure 4d-e). Therefore, owing to light-induced promotion of electron injection and activation into epoxides, Mg-NC exhibited excellent catalytic activity.

Conclusion and Outlook:

In summary, this article reports a carbon-based biomimetic enzyme heterogeneous material with abundant Mg-N₄ single-atom active centers, achieving high stability and activity in photocatalytic CO₂ chemical fixation, providing new insights into the design and construction of biomimetic enzyme heterogeneous photocatalysts.

Article Details:

Artificial Chlorophyll-like Structure for Photocatalytic CO₂ Chemical Fixation

Lei Li^†, Wenxiu Liu^†, Hanghao Ying^†, Xin He, Shu Shang, Peng Zhang, Xiaodong Zhang*, Shuhu Liu*, Hui Wang, and Yi Xie*

Cite this by DOI: 10.31635/ccschem.024.202404189

Article Link: https://doi.org/10.31635/ccschem.024.202404189