Probing the Nature of the Single-Atom Sites in Single-Site Alloy (SAA) Catalysts

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Solid catalysts - used to speed up chemical reactions - are very common in industry and used in approximately 80% of all chemical processes. Solid catalysts are applied to increasingly complex reaction systems. The main challenge of catalyst selection and use is the need to better control which product or products are formed (selectivity). In this project, Professor Francisco Zaera of the University of California, Riverside is exploring the use of single-atom alloy (SAA) catalysts as a way to improve reaction selectivity. This new class of catalysts is a new and promising approach towards both high selectivity and high activity in important classes of industrially reactions. The ability to promote the selective hydrogenation of chemical compounds promises to impact processes in the food, cosmetics, pharmaceuticals, and fine chemicals industries. In general, more selective catalytic processes lead to important benefits such as lower raw material consumption, increased efficiency, and waste minimization - all requirements for more environmentally-friendly processes. The knowledge derived from Zaera's research is used to illustrate basic principles in kinetics, catalysis, and materials synthesis in undergraduate and graduate classes. Professor Zaera is collaborating extensively with Latin American research groups. He encourages student participation from groups underrepresented in research. With funding from the Chemical Catalysis Program of the Division of Chemistry, Professor Francisco Zaera of the University of California, Riverside is developing a fundamental understanding of how single-atom alloy (SAA) catalysts function, with special focus on the use of CuPt bimetallics to promote the selective hydrogenation of unsaturated hydrocarbons. His main hypothesis is that, rather than acting as isolated single atoms as the present state-of-the-art research suggests, the single atoms of the minority component (Pt) may alter the electronic properties of the surface atoms. The Zaera group is probing this idea by following two parallel experimental approaches. His group studies model systems using high-flux molecular beams to emulate the atmospheric pressure conditions needed for catalysis. The team is employing a so-called "high-pressure cell" to carry out in-situ reflection-absorption infrared spectroscopy (IR) experiments during catalysis. Professor Zaera also studies realistic supported catalysts under catalytic conditions, performing in situ IR titrations to identify and quantify the Pt atoms that may segregate to the surface. In-situ X-ray absorption (XAS) spectroscopy is used to evaluate any possible changes in the coordination sphere around the Pt atoms as well as the nature (oxidation state) of the Cu atoms. Professor Zaera emphasizes the recruitment of women and minorities including visiting international students and scholars from Latin America in STEM professions.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.