A ligand design strategy to enhance catalyst stability for efficient formic acid dehydrogenation
Jian Guo1, Maoliang Li2, Chengkai Yin2
1School of Metallurgy and Environment, Central South University, No. 932, Lushan Road, Changsha City, Hunan Province, 410083 China. qitiangui@csu.edu.cn.
Dalton Transactions (Cambridge, England : 2003)
|March 20, 2023
Summary
New iridium catalysts efficiently convert formic acid to hydrogen. These stable catalysts demonstrate high activity and reusability in aqueous solutions, offering a promising route for hydrogen generation.
Area of Science:
- Catalysis
- Organometallic Chemistry
- Green Chemistry
Background:
- Formic acid dehydrogenation (FADH) is a key process for hydrogen production.
- Developing stable and efficient catalysts for FADH in aqueous media is crucial for sustainable energy applications.
- Iridium complexes are known for their catalytic activity but require tailored ligand design for enhanced performance and stability.
Purpose of the Study:
- To synthesize and evaluate novel iridium (Ir) complexes with sulfonamide-functionalized picolinamide ligands for aqueous formic acid dehydrogenation.
- To investigate the catalytic activity, stability, and reusability of these new Ir catalysts.
- To explore the mechanistic aspects of the FADH process using these complexes.
Main Methods:
- Synthesis of iridium complexes featuring N-(methylsulfonyl)-2-pyridinecarboxamide (C1) and N-(phenylsulfonyl)-2-pyridinecarboxamide (C2) ligands.
- Catalytic testing of the synthesized complexes for aqueous formic acid dehydrogenation under various conditions.
- Analysis of catalytic performance including turnover number (TON) and turnover frequency (TOF).
- Stability studies in air and concentrated formic acid, and observation of catalytic intermediates using 1H NMR spectroscopy.
Main Results:
- The synthesized Ir complexes (C1 and C2) demonstrated excellent stability in air and concentrated formic acid.
- Both catalysts achieved complete conversion of formic acid over 20 continuous cycles.
- High turnover numbers (TONs) of 172,916 for C1 and 172,187 for C2 were recorded.
- Complex C1 exhibited a high turnover frequency (TOF) of 19,500 h⁻¹ at 90 °C.
- An air-stable Ir-H species was successfully observed via 1H NMR spectroscopy, providing mechanistic insights.
Conclusions:
- The novel Ir complexes with sulfonamide-containing ligands are highly effective and stable catalysts for aqueous formic acid dehydrogenation.
- These catalysts offer a promising and efficient method for hydrogen generation from formic acid.
- The observed stability and high activity underscore the potential of these complexes in sustainable energy technologies.
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