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Synthesis of Metal Nanoparticles Supported on Carbon Nanotube with Doped Co and N Atoms and its Catalytic Applications in Hydrogen Production
Published on: December 6, 2021
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Isolated metal active site concentration and stability control catalytic CO2 reduction selectivity
John C Matsubu1, Vanessa N Yang, Phillip Christopher
1Department of Chemical & Environmental Engineering, and ‡Program in Materials Science and Engineering, University of California, Riverside , Riverside, California 92521, United States.
Journal of the American Chemical Society
|February 12, 2015
Summary
This study reveals that isolated rhodium atoms and rhodium nanoparticles on TiO2 exhibit distinct catalytic selectivities for CO2 hydrogenation. Nanoparticle disintegration into isolated sites influences catalyst stability and reactivity over time.
Area of Science:
- Heterogeneous catalysis
- Surface science
- Materials chemistry
Background:
- CO2 hydrogenation is crucial for chemical synthesis but its atomic-scale mechanisms remain unclear.
- The influence of metal particle size on catalyst stability, active site distribution, reactivity, and selectivity is critical but often overlooks isolated sites.
- Understanding structure-function relationships in CO2 reduction is essential for developing efficient catalytic processes.
Purpose of the Study:
- To quantify the fraction of isolated (Rhiso) versus nanoparticle-supported (RhNP) rhodium sites on TiO2 catalysts.
- To correlate the abundance of Rhiso and RhNP sites with catalytic activity and selectivity in CO2 hydrogenation reactions.
- To investigate the role of nanoparticle stability and transformation into isolated sites on catalyst performance over time.
Main Methods:
- Utilized diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) with probe molecules to differentiate and quantify Rhiso and RhNP sites.
- Employed site-specific extinction coefficients for accurate site quantification.
- Performed catalytic reactions (reverse water-gas shift and methanation) to assess activity and selectivity.
Main Results:
- Established strong correlations between the turnover frequency (TOF) for reverse water-gas shift and the fraction of Rhiso sites.
- Observed a correlation between methanation TOF and the fraction of RhNP sites.
- Demonstrated that nanoparticle disintegration into Rhiso sites under reaction conditions governs changes in catalyst reactivity and stability over time.
Conclusions:
- Isolated atoms and nanoparticles of the same metal (Rh) on the same support (TiO2) exhibit distinct catalytic selectivities for competing reaction pathways in CO2 hydrogenation.
- The dynamic transformation of Rh nanoparticles into isolated sites significantly impacts catalyst stability and performance.
- This work highlights the importance of considering both isolated atoms and nanoparticles as active sites in heterogeneous catalysis.
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