Molecular Conversion for Sustainable Chemistry
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Until now, the chemical industry has relied primarily on petroleum-based resources as raw materials. However, petroleum is a finite resource, and its production generates significant greenhouse gas emissions, leading to serious environmental concerns. As a result, there has been increasing interest in utilizing abundant and inexpensive resources such as atmospheric nitrogen (N2) and carbon dioxide (CO2) to synthesize valuable compounds. Such molecular transformations are essential technologies for ensuring the sustainability of the chemical industry.
These molecules, however, are chemically stable and thus exhibit low reactivity, often requiring high energy input for conversion. A representative example is the Haber-Bosch process for converting nitrogen into ammonia, which proceeds under high temperature and high pressure, consuming about 1–2% of global energy. Therefore, the development of new reaction pathways and catalytic systems capable of driving these transformations under milder conditions is needed.
Electrochemistry and photochemistry are promising approaches that can directly supply energy to molecules through electricity or light, without relying on strong oxidants or reductants. By adopting these methods, it becomes possible to achieve both high reaction selectivity and reduced energy consumption, making them key technologies for the future of environmentally friendly chemistry.
Cooperative Catalysis Inspired by Enzymes
Enzymes in nature possess remarkable abilities to accelerate complex chemical reactions with high precision and speed. Their catalytic activity arises from the cooperation of various amino acid residues located near the active site, which collectively regulate the substrates. Inspired by this mechanism, our center aims to develop “cooperative catalysts” that function through the combination of two or more catalysts or auxiliary ligands.
Such catalytic systems are particularly advantageous for controlling complex reactions that are difficult to achieve with a single catalyst. For example, one metal catalyst may serve as an electron donor, while another catalyst or ligand selectively modulates substrate binding, thereby improving both the rate and selectivity of the overall reaction. This approach closely resembles the mechanisms that operate in biological systems, offering particular benefits in multi-electron transfer reactions and complex molecular transformations involving the breaking and formation of multiple bonds.
Approaches to Enhance Catalyst Stability
In addition to catalytic efficiency, stability and reusability are crucial factors for practical applications. In electrochemical and photochemical reactions, high-energy intermediates (e.g., radicals) are often generated, which can attack and degrade the catalyst itself, leading to deactivation or leaching. These issues severely limit catalyst lifetime and practical applicability.
To address these challenges, our center is investigating strategies such as employing chemically robust multidentate ligands, or immobilizing catalysts onto electrode surfaces through covalent bonding or metal–substrate interactions. Furthermore, we aim to develop single-atom metal catalysts that can simultaneously maintain high reactivity and enhanced stability.
We are also designing systems that immobilize molecular catalysts onto electrode surfaces, where they can serve as electron transfer mediators. This approach enables reactions to proceed efficiently at lower potentials, reducing side reactions while allowing precise control over catalytic selectivity.
Photocatalysts for Efficient Photoelectrochemical Reactions
Photoelectrochemical reactions, which utilize both light and electricity, offer great promise for maximizing reaction efficiency by promoting charge separation. However, the range of photocatalysts suitable for practical applications remains limited, as many materials suffer from short excited-state lifetimes or poor photostability.
Our center seeks to develop organic photocatalysts that exhibit delayed fluorescence, enabled by a small energy gap between singlet and triplet excited states. Such materials can maintain their excited states for extended durations, thereby utilizing light more effectively to drive high-efficiency reactions. In addition, we are working to optimize photoelectrode structures to ensure efficient electron transfer between the photocatalyst and the electrode.
Analytical and Computational Tools
Molecular transformations typically proceed through multiple steps, generating various intermediates along the way. To accurately elucidate these reaction pathways, a comprehensive combination of analytical techniques is required. Our center employs integrated approaches, including electrochemical analysis, infrared (IR) and Raman spectroscopy, and mass spectrometry, to monitor intermediates and products in real time during reactions.
In parallel, we conduct computational chemistry research, performing quantum mechanical calculations based on experimental data to predict and validate reaction pathways and selectivities. By combining computational and experimental insights, we aim to unravel the mechanisms of highly challenging reactions with precision.
Strategic Substrate Design
In complex molecular transformations, multiple competing pathways often occur simultaneously, making it difficult to selectively obtain the desired product. Unwanted by-products frequently arise when intermediates deviate into side reactions. To address this challenge, our center is exploring strategies that introduce substrates capable of rapidly binding intermediates, thereby directing the reaction along the desired pathway.
For instance, if an intermediate reacts quickly with a specific substrate and results in a significant decrease in free energy, that pathway becomes favored, ultimately improving the yield of the target product. This approach is analogous to the way enzymes guide reaction pathways with high selectivity.
Synergistic Photoelectrochemical Reaction Systems
Breaking strong chemical bonds requires substantial energy, which is often supplied through high voltages or high-energy light. However, such harsh conditions can reduce reaction selectivity and damage catalysts or electrodes. To overcome these limitations, our center is developing strategies that involve exciting electrochemically oxidized or reduced catalytic intermediates with light, thereby generating more powerful oxidants or reductants.
This approach combines modest electrical and light energy inputs to safely and efficiently drive high-energy reactions. Our ultimate goal is to develop new photocatalysts that can maintain high stability and long-lived excited states, even under such demanding conditions.
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