(575al) Adsorption and Reaction of Methanol on Ceria and Au-Ceria: Influence of Ceria Structure

Clean and efficient hydrogen production is of interest because of hydrogen's potential to be the energy carrier of the future. Methanol has been identified as a good source of hydrogen, because of its high hydrogen/carbon ratio, safe handling and easy synthesis from renewable and fossil fuels. Methanol steam reforming can be used as an on-site source of H₂ for fuel cells. The catalytic decomposition of methanol and the water-gas shift reactions comprise the steam reforming reaction for some catalyst systems. A fundamental understanding of the interaction of methanol with the metal and support surfaces is important in the development of active and stable methanol steam reforming catalysts. Temperature programmed decomposition of methanol is a good way to probe this interaction, and is the subject of this investigation.

We have recently identified a strong shape/crystal plane effect of ceria on the activity of 1%Au-CeO₂ catalysts for the water-gas shift reaction ^[1]. We have now extended this investigation to the methanol decomposition and steam reforming reactions. From the literature, it is well known that methanol decomposition on ceria is structure sensitive ^[2,3]. These studies were conducted in vacuum over single crystals of ceria. Here, we have worked at regular pressures, by preparing specific shapes and crystal planes of ceria at the nanoscale. Gold or another metal is then added on the specific crystal facets and the reaction dependence on structure can be easily evaluated.

Ceria nanorods, nanocubes and nanopolyhedra were synthesized by the hydrothermal method, and the corresponding gold doped ceria samples were prepared by the deposition/precipitation method ^[1]. CH₃OH-TPD was used to determine reaction onset, interaction with surface hydroxyls and H₂ selectivity. In the case of pre-reduced ceria, methanol interacts more strongly with the ceria nanorods (110) surfaces, followed by nanopolyhedra (111) surfaces and nanocubes (100) surfaces. Gold facilitates the formation of hydrogen at lower temperatures and greatly inhibits the formation of CO. TEM, XPS and H₂-TPR analyses were also used to investigate the interaction between gold and different planes of ceria.

References:

1. R. Si, M. Flytzani-Stephanopoulos, Angew. Chem. Int. Ed., 47 (2008) 2884.

2. R. M. Ferrizz, G. S. Wong, T. Egami, J. M. Vohs, Langmuir, 17 (2001) 2464.

3. D. R. Mullins, M. D. Robbins, J. Zhou, Surf. Sci., 600 (2006) 1547.