| Supported precious metal heterogeneous catalysts serve an important role in both environmental emission control and emerging energy technologies such as fuel cells. Structural and chemical characterization of these materials is needed in order to develop catalysts with improved activity, selectivity, and stability. In this work, the structure and morphology of nanostructured heterogeneous catalysts were investigated using a variety of materials characterization techniques, including x-ray diffractometry, high resolution transmission electron microscopy, aberration corrected electron microscopy, and z-contrast scanning transmission electron microscopy. The objective of this study is to investigate how catalyst stability and performance are affected by morphology and composition.;Three catalyst systems are presented in this work. The first is Pt-alloy catalysts for proton-exchange membrane fuel cells. Although initially larger than pure Pt catalyst particles, PtCo alloy catalyst particles coarsen at a lower rate during electrochemical testing. Moreover, the lognormal shape of the resultant particle size distribution yields some indication of the mechanisms of catalyst deactivation.;The second catalyst system presented in this thesis is characterization of nanoscale alumina supported Pt/Pd bimetallic alloy catalysts for NO oxidation. In the Pt-Pd bimetallic catalysts study, we investigated both the effect of alloying and the effect of precursor materials on morphology, stability, and performance. HRTEM revealed that, for materials fabricated from both nitrate and acetylacetonate precursors, alloying Pt with Pd resulted in an improvement in thermal stability, while catalytic testing indicates that alloying has little effect on NO conversion.;The third topic in this thesis involves investigating the fundamental interactions of Pd and Rh on ceria (CeO2) and ceria-based supports. This study combines cross sectional HRTEM with theoretical calculations and simulations to determine the fundamental interactions between precious metals and the support surface.;All of these projects are part of larger collaborative efforts to relate catalyst morphology to cost, performance, and reliability. To make progress toward this goal, data from structural characterization of catalyst materials are combined with chemical and electrochemical measurements of these materials to provide direction for research and manufacturing. |
