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The ever-evolving active site: transformation of single atoms to extended structures during the Rh-catalyzed reverse water-gas shift reaction
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DOI：10.1039/d5fd00172b.png)
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Abstract
En 中文
At low temperatures (<400 degrees C), single atoms of Rh supported on rutile TiO2 (rTiO(2)) are responsible for the formation of CO during the reverse water gas shift (RWGS), while methane production is associated with the Rh-TiO2 interface due to the observed correlation between methane formation rates and the volume-averaged Rh nanoparticle diameter. As the temperature is increased to >540 degrees C, there is a notable increase in CO selectivity as the methane production rates tend towards zero. The time to reach zero depends on the temperature but is independent of the initial Rh structure (single atoms and/or nanoparticles), which is controlled by the catalyst preparation method (wetness impregnation versus colloidal nanoparticles). At 600 degrees C and >4 h time on stream, the catalytic behaviour becomes completely agnostic to the initial Rh structure as well as weight loading, and the catalysts are highly selective for the RWGS reaction. Post-reaction HR-TEM image analysis confirms Rh nanoparticles crystallize/order during the reaction; at 400 degrees C, most of the Rh particles are disordered, while at 600 degrees C, they are more ordered (i.e., there is the development of defined faceting). Infrared spectroscopy of CO adsorption on Rh nanoparticles confirms the appearance of defined facets after annealing in nitrogen at high temperatures. Annealing the Rh/rTiO(2) catalysts prior to the RWGS reaction demonstrates the structural transformation of Rh depends only on time and temperature and not on reactant or product fugacity. Sites responsible for stabilizing Rh single atoms are no longer competent at higher temperatures, enabling single atom integration into existent nanoparticles. As the reaction temperature is increased to temperatures >540 degrees C, the dominant Rh structure for CO production evolves from single atoms to extended surfaces.
Keywords:
THERMAL-DESORPTION
CO2 HYDROGENATION
RHODIUM
ADSORPTION
RH(100)
NANOPARTICLES
SELECTIVITY
MOLECULES
KINETICS
FOIL
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