Use of hydrogen as a localized energy source for fuel cell powered vehicles or electronic devices is a promising way to extend range and reduce pollution. Several problems associated with onboard storage of molecular hydrogen can be eliminated by on-board catalytic production of hydrogen from a high-energy liquid fuel such as methanol. Both Pd-Zn and Cu/ZnO based catalysts are well known as active and selective catalysts for oxidative methanol reforming reactions1,2. Our group has previously identified a combination of both copper and palladium active species and promoters enhanced catalytic activity greater than either active species alone3. This work identifies the structure, oxidation and alloy state of palladium and copper in the catalysts both in-situ and reaction conditions using a variety of characterization techniques.

Catalysts containing combinations of copper, zinc, zirconium, and palladium oxides were prepared via co-precipitation or impregnation techniques. Starting with a simple copper and zinc oxide catalyst; activity, structural characteristics, and oxidation states under reaction conditions are examined upon incorporation of ZrO2 and palladium into the catalyst. Catalyst powders were analyzed via elemental analysis, x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), x-ray absorption spectroscopy (XAS) at both Cu and Pd k edges, N2O decomposition, and BET surface area measurement. Catalyst stability and the nature of the deactivated catalyst was measured by running the catalyst for 100 hours then characterization by XRD, and Pd and Cu XAS.

Addition of ZrO2 yielded significant structural enhancements, such as copper surface area and smaller crystallite size, with little impact on catalytic activity. On the other hand, addition of palladium had almost no effect on structural characteristics, but a significant difference in catalytic activity was observed. XAS shows that the oxidation state of copper under reaction conditions is modified by the presence of palladium, and that palladium forms unstable alloys on reduction in hydrogen at moderate temperatures. The deactivated catalyst showed formation of new crystalline oxide phases and growth of copper and palladium alloy particles. The effects of the alloy formation and catalyst structure on catalytic activity are also discussed.

1. Cubeiro, M.L. and Fierro, J.L.G. Jor. of Catal. 179, 150-162 (1998).

2. Cheng, W.H. Appl. Catal A: General 130, 13-30 (1995).

3. Schuyten, S.J. and Wolf, E.E. Catal. Lett. 106, 7-14 (2006).