Collaborative Research: Seeing Adsorbates on Nanoparticles: A Correlated Atomic Resolution Imaging and Spectroscopy Investigation of Supported Metal Catalysts

Arizona State University, Scottsdale AZ

Investigators

Abstract

Catalysis plays a central role in mitigating emissions associated with chemicals, fuels, and materials manufacturing by facilitating chemical transformations with minimal required energy inputs and high selectivity. Many of the most promising energy conversion and storage options associated with renewable and sustainable energy rely on catalysis. To develop cost-effective, environmentally benign chemical conversion technologies, it is necessary to continue to deepen our understanding of the fundamental steps in catalytic processes. Many technologically relevant catalytic processes take place on the surfaces of small particles, so-called nanoparticles. Incoming reactant molecules interact with these surfaces and are transformed into new product molecules. Many of the details of how the particle surface facilitates those transformations are still not well understood. Direct observation of molecule-surface interactions will aid the design of more durable and effective catalysts. As a first step towards realizing this goal, it is necessary to directly see reactant molecular layers on nanoparticle surfaces. The goal of the project is to discover how to make such observations of individual molecules on nanoparticle surfaces, and correlate the observations with spatially averaged information obtained by Fourier Transform Infrared Spectroscopy (FTIR). To visualize molecules on nanoparticle surfaces, the project will correlate signals from in situ atomic resolution transmission electron microscopy with in situ FTIR spectroscopy recorded from catalysts with well-defined nanostructures (matching exposure conditions in the respective environmental chambers). The recent availability of newly developed, high sensitivity electron detectors now makes it feasible to sense adsorbate layers on surfaces using electron microscopy, but it is not clear how to optimize the experimental conditions to make such observations a reality. Infrared spectroscopy will provide spatially averaged information on the characteristics of the surface sites where adsorbate binding is most likely to occur. This spectroscopy will direct the electron microscopy to surface regions where the concentration of molecules is high, so that optimum conditions for molecular imaging can be discovered. The investigation will focus on CO oxidation and NO reduction with CO over supported metal catalysts - two reactions of fundamental interest with broad impact on energy and environmental technologies. Specifically, this research will provide information on the heterogeneity of the adsorbate layer structure and dynamics at terrace, edge, facet, and defect sites on nanoparticle surfaces during catalysis. Spatially resolved characterization of real adlayer structures will provide fundamental new insights on the nature of nanoparticle surfaces giving more accurate foundational information for developing structure-reactivity relations. The research will enhance fundamental knowledge of adsorbate structure and dynamics leading to new approaches to catalyst design. The project will provide education and outreach activities to students and the public in the fields of catalysis, nanoparticles, atomic resolution electron microscopy and infrared spectroscopy. 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.