Highly concentrated hydrogen and carbon nanofibers were produced through methane decomposition in a temperature range of 973-1123 K. Pd-based alloys containing Ni, Co, Rh, or Fe showed high catalytic activity and tong life for methane decomposition at 973 K. In particular, Pd-Co/Al2O3 and Pd-Ni/Al2O3 showed the highest hydrogen yield at reaction temperatures above 973 K among all the catalysts tested. Highly concentrated hydrogen (> 94 vol%) was formed by methane decomposition over Pd-Co/Al2O3 at 1123 K. SEM images of catalysts [M/Al2O3 (M = Fe, Co, Ni, and Pd) and Pd-M/Al2O3 (M = Fe, Co, Ni, Cu, Ag, and Rh)] after methane decomposition showed the formation of carbons with fibrous structure. In addition, TEM images of Pd-Co/Al2O3 at the initial stage of reaction showed that Pd-Co alloy particles formed carbons from several facets, whereas Co or Pd metal particles formed carbon nanofibers from one facet. This would be one reason why Pd-Co alloy catalysts showed high activity and long life for methane decomposition at high temperatures. (c) 2006 Elsevier Inc. All rights reserved.