(491b) Development of Highly Active Nanoscale Catalysts for Production of CΟ Free Hydrogen by Dehydrogenation of Methane

Hydrocarbon decomposition is an alternate route for producing CO free hydrogen in order to satisfy the requirement of polymer electrolyte membrane (PEM) fuel cells. In previous work, Fe-M (M=Pd, Mo, Ni) bimetallic catalysts on γ-Al₂O₃ support prepared by traditional methods, such as impregnation and incipient wetness, were developed by our research group for methane catalytic dehydrogenation. The catalysts lowered the decomposition temperatures of methane by 400-500 ºC and achieved ~70-90% conversion of undiluted methane into pure hydrogen and multi-walled carbon nanotubes at 650-800 ºC with a space velocity of 600 mlhr^-1g^-1. However, the metal particle size of the catalysts could not be well controlled and it was difficult to clean the potentially valuable carbon nanotube (CNT) product because of the difficulty of dissolving the alumina support. Here, we have employed a new method developed by Hyeon et al (J. Park, K. An, Y. Hwang, J-E. Park, H-J. Noh, J-Y. Kim, J-H. Park, N-M. Hwang and T. Hyeon, Nature Materials, 3 (2004) 891-895) to prepare mono-sized Fe and Fe-Ni nanoparticles, which we dispersed over a Mg(Al)O support for use in methane decomposition at temperatures below 700 ºC. The monodisperse nanoparticles were prepared by thermal decomposition of a metal-organic complex in an organic-phase solution and the Mg(Al)O support was prepared by co-precipitation in aqueous solution. This new catalyst has several advantages: (1) it has high activity and long life times; (2) the carbon nanotubes (CNT) are produced in the form of multi-walled nanotubes (MWNT) with uniform diameter and are be easily purified by dissolving the Mg(Al)O support using dilute HNO3 solution. These novel catalysts were characterized by high resolution TEM (HRTEM), scanning transmission electron microscopy (STEM), X-ray powder diffraction (XRD), Mössbauer spectroscopy, and X-ray absorption fine structure (XAFS) spectroscopy.