Active Nb2O5-supported nickel and nickel-copper catalysts for methane decomposition to hydrogen and filamentous carbon

Production of CO-free hydrogen and filamentous carbon via methane decomposition were carried out over Nb2O5-supported nickel and nickel-copper catalysts in a fixed-bed-reactor at atmospheric pressure. The results indicate that Nb2O5 is an effective support for Ni catalysts for methane decomposition to hydrogen. The addition of Nb2O5 increases the yield of hydrogen and carbon capacity of high loading bimetallic Ni-Cu catalysts, and prolongs the lifetime of these catalysts in methane decomposition at high temperature. The maximal yield of hydrogen is 7274 mol H-2/mol Ni for 65Ni-25Cu-5Nb(2)O(5) catalyst at 600degreesC, which is one of the highest values of the catalysts for methane decomposition reported so far. TPR results show that the reduction temperature of Ni-Cu alloy is lower than that of single Ni- or Cu-supported samples and the well-crystallized Ni-Cu species is formed in bimetallic catalysts. Powder XRD results indicate that the addition of Nb2O5 changes the morphology in oxidized state and increases the relative intensity of Ni(1 1 1) planes in reduced state for Ni-Cu bimetallic catalysts. SEM and TEM images of used catalysts show that the surfaces of the fresh catalyst are completely covered with catalytic filamentous carbon (CFC). The "octopus" carbon and fish-bone-like filaments are formed in the induction period in methane decomposition. The filaments formed in the steady state and in the deactivation stage are very fragile to be crushed into filaments in very small sizes in length. (C) 2004 Elsevier B.V. All rights reserved.