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Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction
Published on: April 10, 2018
Photoswitching a molecular catalyst to regulate CO2 hydrogenation
Nilusha Priyadarshani1, Bojana Ginovska, J Timothy Bays
1Pacific Northwest National Laboratory, Richland, WA 99354, USA. wendy.shaw@pnnl.gov john.linehan@pnnl.gov.
This study developed photo-responsive rhodium catalysts for CO2 hydrogenation, showing light can tune catalytic activity. The β-alanine rhodium complex demonstrated a 40% rate increase under light, highlighting light-controlled catalysis potential.
Area of Science:
- Organometallic Chemistry
- Catalysis
- Photochemistry
Background:
- Nature utilizes physiological stimuli to regulate catalytic processes.
- Azobenzene's photo-responsive properties offer a pathway to control catalyst structure and activity.
- Rhodium diphosphine complexes are effective catalysts for CO2 hydrogenation.
Purpose of the Study:
- To incorporate azobenzene into rhodium diphosphine catalysts for photo-initiated structural modulation.
- To investigate the effect of photo-induced cis-trans isomerization of azobenzene on CO2 hydrogenation activity.
- To elucidate the structure-activity relationship in these photo-responsive catalysts.
Main Methods:
- Synthesis of rhodium complexes with azobenzene-containing tetradentate ligands derived from non-natural amino acids (β-alanine and γ-aminobutyric acid).
- Characterization using NMR spectroscopy to confirm structural changes upon photo-isomerization.
- Catalytic testing for CO2 hydrogenation under varying light conditions (dark vs. light on).
- Computational studies to analyze structural differences between cis and trans azobenzene isomers.
Main Results:
- The β-alanine rhodium complex exhibited a 40% increase in CO2 hydrogenation rate (TOF 16 s⁻¹) under light (cis-azobenzene) compared to dark conditions (trans-azobenzene, TOF 11 s⁻¹).
- The γ-aminobutyric acid rhodium complex showed no significant rate difference between cis and trans azobenzene conformations.
- Computational studies indicated major structural changes upon isomerization, with subtle, β-alanine specific alterations potentially influencing catalytic activity.
Conclusions:
- Azobenzene incorporation enables photo-modulation of rhodium-catalyzed CO2 hydrogenation activity, particularly for the β-alanine derivative.
- Subtle changes in ligand bite angle and steric strain, influenced by azobenzene conformation, are postulated to affect rhodium hydride hydricity and thus catalytic rate.
- This work demonstrates a promising strategy for developing light-switchable catalysts for CO2 conversion.
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