F-ZrO₂ Based, Solar Driven Photocatalytic Production of High-Purity CO from Formic Acid

Carbon monoxide (CO) with a purity exceeding 99.999% is essential in industries such as CO lasers, environmental monitoring, integrated circuits, and electronics. Conventionally, high-purity CO is produced by separating it from gas mixtures like CO, H₂, and CH₄. Still, this process requires multiple purification steps, making CO one of the most expensive industrial gases [1]. Formic acid (HCOOH) presents a promising alternative for CO production through dehydration (HCOOH → CO + H₂O), offering a high output-to-input value ratio [2]. However, formic acid can decompose via two different pathways: dehydration, which yields CO and water, and dehydrogenation, which produces CO₂ and hydrogen. To achieve high-purity CO, it is crucial to favor the dehydration pathway. Traditional catalysts have shown promise by reducing the hydrogen content to as low as 0.2%, but trace amounts of hydrogen remain, necessitating additional purification steps [3]. A critical challenge remains to improve catalyst efficiency to minimize hydrogen formation and explore methods for removing hydrogen during CO production. The study of Li et al. [4] aims to address this challenge by exploring sunlight-driven methods for CO production (Figure 1). Theoretical calculations were utilized to identify suitable catalysts for formic acid dehydrogenation, revealing that pure fluorite-structured ZrO₂ could effectively exclude formic acid dehydrogenation intermediates. A synthesis method was developed to produce pure fluorite ZrO₂ nanomaterials capable of directly generating high-purity CO from formic acid. The pure fluorite ZrO₂ nanosheets exhibited a stable thermal formic acid CO production rate of 55 mmol g⁻¹ h⁻¹ at 250 °C, with no hydrogen impurity. Furthermore, assisted by a TiC/Cu-based photothermal reactor, the pure fluorite ZrO₂ nanosheets achieved a photothermal CO production rate of 83 mmol g⁻¹ h⁻¹, along with an exceptionally high solar-to-chemical efficiency of 12.3% under 0.5 sun irradiation. In situ testing further validated their theoretical predictions, demonstrating that the pure fluorite ZrO₂ surface effectively excludes all formic acid dehydrogenation intermediates. In addition, under ambient solar irradiation, the system achieved 1538 L m⁻² of pure CO production per day, corresponding to an estimated input-output profit of US$18,714 m⁻² per year. Overall, the study of Li et al. [4] represents a groundbreaking innovation in high-purity CO production, showcasing the remarkable use of a sunlight-driven system for CO generation. The clever integration of pure fluorite-structured ZrO₂, produced through an explosion method, ensures exceptional stability and hydrogen-free CO output, pushing the boundaries of scientific ingenuity. With outstanding solar-to-chemical efficiency and scalability, this work offers a transformative, eco-friendly solution that reshapes the future of industrial CO production. While this study represents a significant breakthrough, there are a few areas for further enhancement. On one hand, enhancing the long-term stability and anti-poisoning ability of the catalyst is crucial for sustained and efficient operation. On the other hand, conducting a comprehensive life cycle assessment to evaluate the system’s environmental impact and overall performance would provide valuable insights for further improvements. Despite the challenges, the solar-driven formic acid dehydration technology for high-purity CO production holds promising potential, with the prospect of achieving more efficient, cost-effective, and environmentally friendly industrial applications in the future.