CAS-Climate: Spectromicroscopy of Elementary Steps in Catalytic Reactions

With support from the Chemical Measurement and Imaging (CMI) Program in the Division of Chemistry, a research team led by Professors Wilson Ho and Ruqian Wu from the Departments of Chemistry and Physics and Astronomy, respectively, at the University of California-Irvine is developing a sophisticated measurement approach for studying the catalytic chemistry of carbon dioxide, an important greenhouse gas. This research has the potential to provide fundamental understanding that is needed to help develop the chemistry of carbon sequestration a very important environmental/climate science goal.

An important objective is the application of sophisticated measurement tools to probe the mechanism for conversion of carbon dioxide to higher-value hydrocarbons using single-atom catalysts. Catalysis by single metal atoms deposited on a substrate enables conservation of valuable metals. This project will examine how metal atoms bind reactants and serve as catalytic centers for directed chemical reactions that are stimulated by electrons and light, rather than by heat.

The team is working to combine chemical measurement and imaging at the atomic scale with theoretical calculations in order to characterize and visualize intermediate species that remain challenging to identify but whose observation would facilitate mechanistic understanding and thereby enable the development of catalysts for targeted reaction courses. This project seeks to provide missing knowledge that is crucial for controlling the chemistry of carbon dioxide while also advancing the state-of-the-art in precision measurement and theoretical methodology for studying the chemistry of single-atom catalysts.

In addition to addressing one of the most consequential challenges in chemistry and the global implications for moderating climate change, the broader impacts of the work are enhanced by the emphasis on basic principles of chemical reactions that are transferrable to the classroom. Broader impacts of the project will include demonstrations involving liquid nitrogen and vacuum for middle school students from nearby underserved communities.

The educational impact of the project will be enhanced through education and outreach activities in collaboration with the University of California-Irvine Eddleman Quantum Institute and the NSF Materials Research Science and Engineering Center, including opportunities to connect with high school students and undergraduate and graduate students from surrounding universities.

The nature of complex interactions between atoms, molecules, and substrates has for many years confounded insights into catalytic reactions. The design of effective catalysts is among the most urgent fundamental and technological challenges for energy harvesting and environmental protection. Chemical reactions occur rapidly and often indiscriminately in complex environment and at elevated temperature, and details of the reactions are difficult to obtain by density functional theory calculations and large ensemble statistical experiments.

It is desirable to be able to measure and control chemical reactions step-by-step and associated intermediate species. This research explores with the scanning tunneling microscope (STM) the smallest catalytic centers in chemistry: a single active atom on an inert two-dimensional van der Waals monolayer or ultrathin insulating film. The reactions under study will proceed by inducing with different stimuli: mechanical motion of the tip, tunneling electrons, and light illumination.

Furthermore, the spectro-microscopy capability is expected to provide direct real-space visualization of individual chemical bonds and skeletal structure of the chemical species. A deeper understanding of the local chemistry and reaction kinetics will rely on first-principles calculations to explain the data and make predictions to guide the experimental effort.

This project will focus on the reduction of carbon dioxide to value-added hydrocarbons as fuels and will examine intermediate species with different electronic, vibrational, spin, structural, and energetic properties. The combined experiment-theory effort is designed to identify and identify these species and provide molecular-level information about their properties.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.