Electron microscopy characterisation of size-selected Pd clusters and industrial Pd catalysts

Pearmain, David (2011). Electron microscopy characterisation of size-selected Pd clusters and industrial Pd catalysts. University of Birmingham. Ph.D.

Preview

Pearmain11PhD_r.pdf
PDF
Download (13MB)

Abstract

This thesis presents an investigation into the morphology of palladium (Pd) size selected clusters and industrial Pd catalysts using high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) technique. The driving force of this work is to establish reliable and efficient methods for the structural characterisation of nanostructures. The characterisation of nanostructures is essential to our fundamental understanding of cluster use within applications, such as catalysis. The complexity of the morphology of industrial catalysts presents a significant challenge to rapid screening techniques. This thesis presents an efficient method which uses size selected clusters as mass standards in STEM based mass spectrometry. Size selected clusters were created using a radio frequency magnetron sputtering cluster beam source in conjunction with a lateral time of ight mass selector, Pd clusters were soft-landed onto amorphous carbon grids between the size range of N = 454 to 10,000 (\(\pm\)4%), with a deposition energy of 500 eV. The quantitative image analysis allows one to gain insight into each catalytic Pd particle and, in combination with two-dimensional diameter measurements, evaluate the three dimensional morphology of the particles. The use of the cluster source has also allowed investigation into the formation mechanisms of nanostructures, finding specific size-dependant morphological features for Pd clusters. Elongation of Pd clusters has been observed for cluster sizes of \(\geq\) 2000 atoms, as well as the onset of voids within the cluster structure for sizes \(\geq\) 2622. HAADF-STEM analysis has proved to be an invaluable tool in the determination of cluster size, independent of morphology, as well as enabling specific structural features within clusters to be revealed. An investigation into the atomic structure of supported Pd\(_{887}\) clusters is also presented. Specific structural motifs are identified using aberration corrected STEM within the sample range via direct comparison with simulated HAADF-STEM images of structures simulated using global minimum techniques.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):