The precious metals, such as platinum, palladium and rhodium, in catalytic converters make the vehicle devices attractive to thieves, but University of Central Florida researchers are working to reduce the amount of precious metals needed in them — down to single atoms — while still maximizing their effectiveness.
Catalytic converters, which were widely introduced in American vehicles in the 1970s, use precious metals as catalysts to help scrub deadly and harmful chemicals from combustion engine exhaust. As the price of precious metals has continued to rise, so has the number of catalytic converter thefts.
In recent studies appearing in Nature Communications and the Journal of the American Chemical Society, UCF researchers showed that they could, respectively, use atomic platinum to control pollutants and operate the system at lower temperatures, which is crucial to removing harmful chemicals when a vehicle first starts.
Fine-tuning Platinum Atom Location
In the Nature Communications study, UCF research teams led by Fudong Liu, assistant professor in the Department of Civil, Environmental and Construction Engineering, and Talat Rahman, distinguished Pegasus Professor in the Department of Physics, successfully constructed platinum single atoms with different atomic coordination environments at specific locations on ceria. Ceria is a metal oxide that helps improve catalytic reaction performance.
Liu and Rahman are also affiliated with the Catalysis Cluster for Renewable Energy and Chemical Transformations (REACT).
The platinum atoms exhibited strikingly distinct behaviors in catalytic reactions, such as carbon monoxide oxidation and ammonia oxidation in a diesel engine exhaust aftertreatment system, the researchers say.
The oxidation converts deadly carbon monoxide to carbon dioxide, and harmful ammonia to nitrogen and water molecules.
Their results suggest that the catalytic performance of single atom catalysts in targeted reactions can be maximized by optimizing their local coordination structures through simple and industrial-scalable strategies, Liu says.
“By combining electronic structure calculations with state-of-the-art experiments, the Liu and Rahman teams have made a breakthrough that can significantly benefit the heterogenous catalysis community in designing highly efficient single atom catalysts for both environmental and energy related needs,” Liu says.
“We have successfully developed a facile strategy to selectively fine-tune the local coordination environment of platinum single atoms to achieve satisfactory catalytic performance in different target reactions, which will push the understanding of single-atom catalysis a significant step forward,” he says.
Rahman says their collaborative work demonstrates how theory and experiments working in tandem can unveil microscopic mechanisms responsible for enhancing catalytic activity and selectivity.
Efficient Carbon Monoxide Oxidation Catalyst
In the Journal of the American Chemical Society study, Liu and collaborators from Virginia Tech and Beijing University of Technology significantly improved the carbon monoxide purification efficiency of a platinum-ceria-alumina catalyst by 3.5 to 70 times compared to the regularly used platinum catalysts.
They did this through the precise control of coordination structures of platinum at the atomic level on an industrial-available ceria-alumina support.
“The local structure of the active site within a catalyst determines its catalytic performance,” Liu says. “However, the precise control of the local coordination structure of active sites and the elucidation of intrinsic structure-performance relationships are of great challenges in the heterogeneous catalysis field.”
“We’ve worked to control the local coordination structure of metal sites at an atomic level, develop a highly efficient catalyst in environmental purification related reactions and reveal the structure-performance relationship of the newly fabricated catalysts for guiding the future catalyst design,” he says.
Using a surface defect enrichment strategy, Liu and his team reported the successful fabrication of platinum atomic single-layer and platinum single-atom structures with precisely controlled local coordination environment on ceria-alumina supports.
Using high-angle annular dark-field scanning transmission electron microscopy, one of the key coauthors, Yue Lu from Beijing University of Technology, directly observed that the platinum atomic single-layer and platinum single-atom structures showing 100% metal exposure were embedded into ceria lattice or adsorbed on ceria surface.
The embedded platinum atomic single-layer site showed the highest efficiency in carbon monoxide purification, which was 3.5 times of that on the adsorbed platinum atomic single-layer and 10 to 70 times of that on platinum single-atom sites.
In collaboration with Hongliang Xin’s research group at Virginia Tech, from both experimental and theoretical aspects, the team concluded that the unique embedded platinum atomic single-layer structure could promote the activation of interfacial oxygen species and thus benefit the carbon monoxide oxidation at low temperatures.
The work is highly important because it will help the environmental catalysis community better design more active metal catalysts with 100% metal utilization efficiency for targeted environmental applications, Liu says.
“We showed how to control and utilize the structures of metal single-atom, atomic single-layer and cluster sites in emission control related reactions, and how to understand their structure-performance relationship using both experimental and theoretical simulation approaches,” Liu says. “This will pave the way for future environmental catalyst design at the atomic level and achieve high efficiency in practical applications.”
Authors and Acknowledgements for the Nature Communications Study
Study co-authors were Wei Tan, Shaohua Xie, Duy Le and Dave Austin from UCF; Weijian Diao from Villanova University; Meiyu Wang, Fei Gao and Lin Dong from Nanjing University; Ke-Bin Low from BASF Corporation; Sampyo Hong from Brewton-Parker College; and Lu Ma and Steven Ehrlich from the National Synchrotron Light Source II (NSLS-II), Brookhaven National Laboratory.
The study was supported with funding from the U.S. National Science Foundation grant and Startup Fund (Liu) from UCF. Xie was partially supported by UCF’s Preeminent Postdoctoral program.
Authors and Acknowledgements for the Journal of the American Chemical Society Study
Study co-authors were Shaohua Xie and Kailong Ye from UCF; Liping Liu from Virginia Tech; Chunying Wang, Yaobin Li and Yan Zhang from the Chinese Academy of Sciences; Sufeng Cao and Maria Flytzani-Stephanopoulos from Tufts University; Weijian Diao from Villanova University; Jiguang Deng from Beijing University of Technology; Wei Tan, a visiting doctoral student at UCF from Nanjing University; and Lu Ma and Steven Ehrlich from the National Synchrotron Light Source II (NSLS-II), Brookhaven National Laboratory.
The work was supported by the Startup Fund (Liu) from UCF and UCF’s Preeminent Postdoctoral program (Xie).
Liu is an assistant professor in the Department of Civil, Environmental, and Construction Engineering, part of UCF’s College of Engineering and Computer Science, and a core faculty in the Catalysis Cluster for Renewable Energy and Chemical Transformations (REACT) at UCF. Prior to his appointment at UCF, he worked at BASF Corporation as a senior chemist developing new concepts and catalyst technologies for vehicle emission control. Now, his research interests are mainly focused on heterogeneous catalysis for pollution control, greenhouse gas reduction/ultilization and clean energy source conversion. These topics include single atom catalysis, nanomaterial synthesis and catalysis, automotive emission control, CO2 and CH4 utilization, H2 production, etc. Liu has published 121 peer reviewed papers with more than 9,200 citations and H-index of 48 (Google Scholar), four book chapters and applied 41 patents in environmental catalysis field.
Rahman is a trustee chair professor and Pegasus Professor in the Department of Physics, part of UCF’s College of Sciences, and leads the faculty cluster in Renewable Energy and Chemical Transformations (REACT) at UCF. She joined UCF as chair of physics in 2006, prior to which she was a university distinguished professor at Kansas State University. Her research interests are in computational design of functional nanomaterials through microscopic understanding of their physical and chemical properties. At UCF, she has led the effort to transform undergraduate instructions by infusing active learning environments. She is a fellow of the American Association for the Advancement of Science; the American Physical Society; AVS: Science and Technology of Materials, Interfaces and Processing; and Royal Society of Chemistry (UK). She is also the recipient of several professional awards including the Research Incentive and Excellence awards from UCF, Visiting Miller Professorship from University of California-Berkeley, Alexander von Humboldt Research Prize, Higuchi Research award from the University of Kansas, and the Distinguished Graduate Faculty award, Kansas State University. She has published more than 320 refereed papers, mentored over three dozen doctoral students, and engaged in promoting scientific collaborations in developing countries. Her work has been cited over 10,700 times. She has also been involved in efforts to promote the participation of women and minorities, particularly through the Bridge program of American Physical Society.