Promoting effects of doping ZnO into coprecipitated Ni-Al2O3 catalyst on methane decomposition to hydrogen and carbon nanofibers

ZnO was doped into coprecipitated Ni-Al2O3 catalyst to promote the activity and the stability in methane decomposition to hydrogen and carbon nanofibers. The promoting effects were examined with XRD, TPR, XPS and TEM, using an in situ thermal balance reactor and a tubular fixed-bed reactor. The results showed that there was a strong interaction between Ni-Al2O3 and the doped ZnO, which may result in the formation of ZnAl2O4 spinel-like structure. The doping of ZnO could improve both the activity and the stability of nickel particles in methane decomposition. Such promotion effects became more pronounced with the increase of ZnO content. The evolution of the morphologies of the carbon produced and of the catalyst particles with the reaction temperature suggested that the doping of ZnO may delay the appearance of the quasi-liquid state of the catalyst particles to the range of higher temperatures and may weaken the interfacial wetting effect between catalyst particles and the growing carbon layers to delay the encapsulation process of the catalyst particles. (c) 2007 Elsevier B.V. All rights reserved.