MATERIALS SCIENCE AND ENGINEERING

SEMINAR

MSE PhD Final Examination

Atomic level study of water-gas shift catalysts

via transmission electron microscopy and X-ray spectroscopy

By:

M. Cem Akatay

Co-Advisors:

Prof. E. Kvam, Dr. E. A. Stach, and Prof. F. H. Ribeiro

ABSTRACT

Water-gas shift (WGS), CO + H₂O → CO₂ + H₂ (ΔH° = -41 kJ mol^-1), is an industrially important reaction for the production of high purity hydrogen. Commercial Cu/ZnO/Al₂O₃ catalysts are employed to accelerate this reaction, yet these catalysts suffer from certain drawbacks like costly regeneration processes and sulfur poisoning. Extensive research is focused on developing new catalysts to replace the current technology. Supported noble metals stand out as promising candidates yet comprise intricate nanostructures complicating the understanding of their working mechanism.

In this study, the structure of the supported Pt catalysts is explored by transmission electron microscopy and X-ray spectroscopy. The effect of the supporting phase and the use of secondary metals on the reaction kinetics are investigated. Structural heterogeneities are quantified and correlated with the kinetic descriptors of the catalysts to develop a fundamental understanding of the catalytic mechanism. The effect of the reaction environment on catalyst structure is examined by in-situ techniques. This study benefitted greatly from the use of model catalysts that provide a convenient medium for the atomic level characterization of nanostructures.

Based on these studies, Pt supported on iron oxide nano islands deposited on inert spherical alumina exhibited 48 times higher WGS turnover rate (normalized by the total Pt surface area) than Pt supported on bulk iron oxide. The rate of aqueous phase glycerol reforming reaction of Pt supported on multiwall carbon nanotubes (MWCNT) is promoted by co-impregnating with cobalt. The synthesis resulted in a variety of nanostructures among which Pt-Co bimetallic nanoparticles are found to be responsible for the observed promotion.  The unprecedented WGS rate of Pt supported on Mo₂C is explored by forming Mo₂C patches on top of MWCNTs and the rate promotion is found to be caused by the Pt-Mo bimetallic entities.

Date:      Monday, November 18, 2013

Time:      8:30 A.M.

Place:     ARMS 1103

Lisa Stacey

Secretary/Development Assistant

Purdue University

School of Materials Engineering

765/494-4100