Novel Fe–Ni nanoparticle catalyst for the production of CO- and CO2-free H2 and carbon nanotubes by dehydrogenation of methane

A novel nanoparticle impregnation method was used to prepare an Fe–Ni nanoparticle (np) catalyst supported on Mg(Al)O for the production of CO- and CO2-free H2 and carbon nanotubes (CNT) by non-oxidative dehydrogenation of methane. This novel catalyst and a catalyst of similar composition prepared by incipient wetness (IW) were evaluated for their catalytic performance and their structures were determined by several microscopic and spectroscopic techniques. Monosized Fe0.65–Ni0.35 oxide nanoparticles with an average particle size of 9 nm were prepared by thermal decomposition of an Fe–Ni oleate–surfactant complex in octadecene under reflux; these nanoparticles were dispersed onto a Mg(Al)O support to form a supported Fe–Ni np/Mg(Al)O catalyst. Compared with the Fe–Ni IW/Mg(Al)O catalyst, the nanoparticle catalyst was more easily reduced at a lower temperature (600 °C in H2) and exhibited enhanced methane dehydrogenation and longer life-times at both 600 and 650 °C. Each reduced Fe–Ni nanoparticle functioned as an active site for the growth of CNT. The CNT were in the form of multi-walled nanotubes (MWNT) of relatively uniform diameter. An invar-like Fe–Ni–C alloy phase is believed to be the active phase for methane dehydrogenation. The deactivation of the nanoparticle catalyst is principally due to encapsulation of catalyst particles by the CNT.

The properties of a monosized Fe0.65–Ni0.35 nanoparticle catalyst for dehydrogenation of methane to hydrogen and carbon nanotubes are demonstrated to be superior to those of a similar catalyst prepared by incipient wetness. Electron microscopic and Mössbauer and XAFS spectroscopic characterization indicate that the active catalytic phase is an invar-like Fe–Ni–C phase and that deactivation occurs principally because of encapsulation of the catalyst within the nanotubes. Figure optionsDownload as PowerPoint slide