PNNL

The Science

Platinum group metals are active catalysts that reduce CO₂ into CO and methane with a high preference for the latter. Both single-metal atoms and metal nanoparticles supported on Fe₃O₄ surfaces catalyze the production of CO, though some studies indicate that single-metal atoms are superior catalysts prompting the assumption that they have different properties. The research presented here refutes this assumption by providing evidence that the Rh-O-Fe bonds of both single Rh atoms and interfaces of supported Rh nanoparticles generate similar chemical environments and display the same catalytic chemistry for CO₂ reduction. This holds for other Pt-group metals as well.

The Impact

Carbon capture, utilization, and storage involves sequestration of CO₂ emissions to prevent their release into the atmosphere. This process can involve the transformation of CO₂ into more usable products. To help us achieve a carbon-neutral future, scientists investigated the mechanism of CO₂ reduction by Pt-group metal catalysts. Their study revealed that the Rh-O-Fe bonds of both single Rh atoms and Rh nanoparticles stabilized on oxidic surfaces catalyze the reduction of CO₂ to CO, while only the metal nanoparticle further hydrogenates CO producing methane. This provides insight into the selectivity of Pt-group metal catalysis supported on oxides.

Summary

Researchers synthesized Rh nanoparticles and single Rh atoms stabilized on Fe₃O₄ surfaces and compared their catalytic activities for CO₂ reduction and methane production. Both Rh atoms at the interface of Rh nanoparticles and Fe₃O₄ and single Rh atoms supported on the same surface form Rh-O-Fe sites. These sites exhibit strong interactions with CO₂ and orders-of-magnitude higher conversion rates of CO₂ than the active sites of metallic nanoparticles. When the stabilizing surface is changed from Fe₃O₄ to SiO₂, this catalytic activity is no longer observed, indicating that the support material and the metal sites directly bound to it play an important role in CO₂ reduction. Ru-O-Fe and Pt-O-Fe sites in single atom catalysts display similar catalytic activities to Rh-O-Fe, indicating that single atoms of the Pt-group have similar physicochemical properties when stabilized on the same surface. This research establishes the importance of metal-O-Fe bonds for CO₂ reduction by metal nanoparticles and single-metal atoms on oxidic surfaces, clarifying earlier reports of decreased activity by nanoparticles.

This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science user facility operated by Argonne National Laboratory and Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by DOE Office of Biological and Environmental Research at Pacific Northwest National Laboratory (PNNL). Computational resources were provided via user grants at EMSL, and the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility in addition to in-house resources from PNNL’s Research Computing facility.

Contact

Oliver Y. Gutiérrez

Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory

oliver.gutierrez@pnnl.gov

Roger Rousseau

Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory

roger.rousseau@pnnl.gov

Funding

This research was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences program, Division of Chemical Sciences, Geosciences and Biosciences and the Canadian Light Source and its funding partners.