The working state of nanoparticle (NP) catalysts might not be the state in which the catalysts were prepared, but a structural and/or chemical isomer that adapted to the particular reaction conditions. This project investigates the dynamic nature of metal NP catalysts and their response to their environment. The intellectual merits are: (1) the development of improved synthetic methods leading to unique NP structures that can be used to achieve a better understanding of structure-reactivity relationships; (2) the advancement of in-situ and ex-situ atomic-level characterization methods suitable for the study of nm-sized particles with variable geometries. Micelle encapsulation methods will be used to produce highly uniform Au and Pt NPs supported on TiO2(110) and gamma-Al2O3. The oxidation of 2-propanol will be used as model reaction. In-situ and ex-situ X-ray absorption spectroscopy (XAS), atomically resolved scanning and environmental transmission electron microscopy (STEM, E-TEM), X-ray photoelectron spectroscopy, scanning tunneling microscopy, and atomic force microscopy will be synergistically combined to characterize the model nanocatalysts.
NON-TECHNICAL SUMMARY:
It is now common knowledge that metal nanoparticles (NPs) possess unique properties as compared to their bulk counterparts, including enhanced chemical reactivities. Despite the enormous industrial and environmental relevance of chemical processes catalyzed by NPs, the origin of the improved catalytic performance is still not well understood. The objective of this research proposal is to improve the understanding of the changes that NPs undergo under industrial reaction conditions, as well as the effect of particle geometry and structure, in particular, shape, on catalytic reactivity. The broader impacts of this study relate to the optimization of existing catalysts and rational design of the future ones by gaining insight into the correlations between the shape and the reactivity of supported metal nanocatalysts. Further, the model reaction selected has broad applications in the fields of energy generation (alcohol fuel cells) and environmental remediation (removal of volatile organic compounds). In addition, this project will support the research efforts of one PhD, three undergraduates (one of them from Stern College for Women at Yeshiva Univ.), and a female K-12 student. The students involved in this project will have access to user facilities available at Brookhaven Nat. Lab. for in-situ catalysis research. Furthermore, the PI and co-PI will include basic concepts related to the present research and online training modules on a bilingual (English-Spanish) outreach website directed to middle-school and K-12 students.
This research is supported by the Solid State and Materials Chemistry program in the Division of Materials Research.
Heterogeneous catalysis is a vitally important technology for industrialized societies, since it is videly used in the manufacturing of chemicals and also in the remediation of environmental pollutants such as automobile exhaust. Due to their prevalent use in catalysis, understanding the fundamental physical and chemical processes that occur on the surface of supported metal nanoparticles (NPs) is critical for designing new, highly efficient and selective catalysts. To this end, the influence of the nanoparticle size, shape, support and oxidation state on reactivity must be well understood. However, it should also be considered that nanoparticles might undergo striking chemical and structural changes during the course of a reaction. To study this highly dynamic and complex properties, well-defined size- and shape-selected metal nanoparticles have been synthesized using reverse micelle encapsulation and characterized using a combination of microscopy and spectroscopy techniques under realistic reaction conditions. By choosing these types of in situ techniques we have worked towards trying to close the gap between laboratory experiments and real world conditions while studying nanoparticle catalysts at work. Grazing-incidence small angle scattering and X-ray absorption fine-structure spectroscopy measurements were used to gain insight into the shape of nanoparticles and its evolution under different thermal treatments and gaseous environments, including reducing and oxidizing conditions commonly employed in catalytic industrial settings. For example, a clear shape transformation from 2D to 3D-like particles was observed with increasing hydrogen pressure. Our work also allowed us to gain knowledge into the correlation between the structure (size and shape), environment (adsorbate and support) and the electronic properties of metal (Au, Pt, Pd, Cu) nanoparticle catalysts.
