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Calendar: ALS Calendar
Title: ALS Seminar: John Evans
When: 10/ 5/2012 1:00 PM - 2:00 PM
Description: ALS Special Seminar

“In situ structural characterization of metal catalysts and materials using XAFS spectroscopy in combination with complementary techniques”

Presented by: John Evans
Chemistry, University of Southampton; Diamond Light Source; Research Complex at Harwell, UK

Friday October 5 2012
1:00pm 15-253 Conference Room

The availability the Third Generation light sources has greatly enhanced the opportunities for investigating chemical change in real time.
This presentation describes studies carried out at the ESRF and Diamond Light Source investigating chemical processes in the solid state and in solution.

- Oxide-based functional materials have been investigated as arrays of differing composition by multi-edge XAFS, powder diffraction and Raman spectroscopy. Examples will include BiMoVOx pigments and LaxBi1-xFeO3 ferroelectrics.

- Supported rhodium catalysts for CO oxidation and NO removal have been investigated by combining mass spectrometry with XAFS, often in conjunction with diffuse reflectance IR spectroscopy. More recent experiments will be described which probe the effect of reducible oxide co-promoters (Ce and Zr) and the performance and structure of the catalysts.

- The nature of catalysts for the selective tri- and tetramerisation of ethene to linear α-alkenes which are generated by treatment of Cr(III) complexes incorporating bi- and tri-dentate soft-donor ligands with aluminium alkyl reagents has been investigated by XAFS spectroscopy. The acquisition time required by conventional scanning mode methods was longer than normal reaction times. Hence a sampling technique combining stopped-flow with freeze-quench techniques has been developed to probe these catalysts..

- A demonstration experiment using a germanium microstrip detector has shown that energy dispersive EXAFS can be employed to investigate the nature of photoexcited states.7 Plans to establish these techniques at the Diamond Light Source will be outlined.
Location: 15-253-CR(80)
Author: jetempler@lbl.gov