The role of PdZn alloy formation and particle size on the selectivity for steam reforming of methanol

FUEL 92

Ayman Karim, akarim@unm.edu1, Travis Conant1, and Abhaya, K. Datye, datye@unm.edu2. (1) Chemical Engineering Department, University of New Mexico, Center for Microengineered Materials, Farris Engineering Center room 203, 1 University of New Mexico, MSC01 1120, Albuquerque, NM 87131, (2) Department of Chemical and Nuclear Engineering, University of New Mexico, Farris Engineering Center, Room 203, Albuquerque, NM 87131
Pd/ZnO has been shown in recent years to possess high selectivity towards CO2 during methanol steam reforming. It is commonly assumed that PdZn alloy formation is essential to achieve high selectivity towards CO2. The simplest method to form a PdZn alloy is to treat a Pd/ZnO catalyst at elevated temperatures in H2, generally > 350◦C. The high temperature treatment, while transforming Pd to PdZn, also leads to particle growth. This makes it difficult to assess independently the role of particle size and composition. In this work, we have used alternative activation treatments in order to vary independently the particle size and extent of alloy formation. We used XRD and TEM to obtain estimates of average crystallite size and composition. The results show that the size of the PdZn alloy particles plays a major role in determining selectivity towards CO2. PdZn alloy particles smaller than 2nm exhibit lower selectivity. We also find that the presence of pure Pd on ZnO is not necessarily detrimental to achieving high selectivity towards CO2.
 

Advances in Hydrogen Production
1:30 PM-5:05 PM, Monday, 11 September 2006 Palace -- Marina Room, Oral

Division of Fuel Chemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006