Professor Bruce E. Koel of Lehigh University is supported by the Chemical Catalysis Program in the Division of Chemistry to prepare bimetallic germanium and tin alloys on platinum surfaces, such as Sn/Pt(111) and Ge/Pt(111), and to form oxide films on these alloys. A sophisticated suite of surface analytical spectroscopy and microscopy techniques will be employed to characterize the alloys with atomic scale resolution and provide information on their structure, composition, and catalytic properties. Structure-property relationships of these systems, required for their development as new catalytic materials, will be established.
The majority of metal-based heterogeneous catalysts are bimetallic or multimetallic systems. The proposed research will lead to a better understanding of how the structure and composition of bimetallic Pt alloy surfaces, and oxide-alloy interfaces affect the chemistry and catalysis of these materials. The results will inform the development of new catalysts with higher selectivity and the rational design of nanoscale materials with improved functionality. Graduate and undergraduate students and postdoctoral associates involved in this research will receive excellent training in chemical catalysis and surface chemistry.
The use of alloys is ubiquitous in technologies ranging from gas sensors to turbine blades, and nearly all metal-based heterogeneous catalysts used for chemical synthesis and conversion are bimetallic or multimetallic systems. Advances in predicting the properties and tailoring the structures of bimetallic interfaces are needed in order to speed progress in developing new catalysts with higher selectivity and designing nanoscale materials with improved functionality. NSF funds were used to improve our understanding of how the structure and composition of platinum alloy surfaces control the chemistry and catalytic reactions that occur at these surfaces. Our goal was to establish detailed structure-property relationships by direct experimental determinations of the structure and measurements of the chemistry of well-defined bimetallic surfaces and reactive sites. Our approach was to specifically prepare surfaces of ordered alloys (i.e., intermetallic compounds) of platinum and another metal that expose only particular alloy sites. This simplifies understanding of the chemistry of more complicated, "real-world" surfaces and enables probing site-directed chemistry – the reactivity of sites with a particular composition and structure. Our studies utilized a multitechnique, surface science approach combining scanning tunneling microscopy to image the surface and high-resolution core-level spectroscopy to provide chemical state information. X-ray photoelectron diffraction and alkali ion scattering spectroscopy was used to determine the atomic structure of the surface layers. Chemistry at these surfaces was probed by temperature programmed desorption and infrared reflection-absorption spectroscopy. Specifically, key results were obtained in the following areas: (i) nature of platinum bimetallic alloys, where. we characterized the surface structure of alloys formed by deposition of copper and zinc on platinum single-crystal substrates, and found large differences in the behavior of germanium deposited on the (111) and (100) crystal faces; (ii) chemisorption and reactions on platinum-tin alloys, where we obtained new insight into adsorption and reaction of acetylene on platinum and two ordered platinum-tin surface alloys, and (iii) surface chemistry and processes at bimetallic electrocatalysts and nanoparticles, where we investigated multimetallic systems and alloys for reducing the amount of platinum needed for electrocatalysts and chemical mechanisms involved in the environmental remediation of heavy metals with iron nanomaterials. This research increased fundamental understanding of catalysis and materials science with potentially important benefits to society via new materials and enhanced catalytic performance. Human resource development included work on this project by graduate students, postdoctoral associates, and undergraduates. This project integrated experimental research with education in the fundamentals of surface science, preparing students well for careers in high-tech and emerging industries, national labs, or academic institutions that utilize state-of-the-art analytical measurements and sophisticated instrumentation and that value the ability to solve complex problems. Results from this research was utilized in courses taught by the principle investigator in "Catalytic Chemistry" and "Surface Science: Processes and Probes".