Ethylene Glycol Adsorption and Decomposition over CeO2 (111) Surfaces

CHEN, TSUNG-LIANG; CALAZA, FLORENCIA C.; OVERBURY, STEVEN H.; MULLINS, DAVID R.

Albuquerque, NM

Simposio; AVS 57th International Symposium and Exhibition; 2010

American Vacuum Society

11:00am SS-ThM10 (Oral - Co-author) SS-ThM10 (Oral - Co-author) Hydrogen production from the reforming of oxygenated hydrocarbons is highly dependent on the heterogeneous reactions provided by its catalysts. Cerium oxide supported metal catalysts can offer a means of reducing precious metal loading and achieving higher selectivity. Thus studying the direct contribution from the metal oxide surface to the decomposition of the molecules can give insight into the catalytic reforming process. In light of our previous characterization on C1-C3 oxygenate reactions on well-defined cerium oxide thin films, we further examine ethylene glycol as a model system for bio-mass derived hydrocarbons. As the simplest diol, ethylene glycol has two symmetric hydroxyl groups which are available to interact with the surface. The absorbates can bond to the surface through either one or both of these oxygens, which may lead to a different decomposition pathways. On the surface of the fully oxidized ceria ethylene glycol appears to initially bond to the surface through only one of the C-O groups. As the temperature is increased both ends interact with the surface and one C-O group is converted into a carboxylate group (COO). The primary reaction products are acetaldehyde, ethylene, acetylene, water and H2. CO desorption was also observed indicating some of the oxygenates experienced C-C bond breaking. On a reduced surface one end of the molecules undergoes C-O cleavage resulting in a C-Ce bond rather than an additional C-O bond. The surface intermediate is a carbanion, similar to what was observed for acetaldehyde. More acetylene is observed from a reduced surface. The dependence of the reaction pathways on the coverage of ethylene glycol was also examined on the oxidized and reduced surfaces. At larger coverage, the formation of carboxylates or carbanions is hindered which sggests that the formation of these species may be sterically limited.