The catalytic decomposition of methane offers an interesting route to obtain a stream of pure COx-free hydrogen and carbon materials in the solid phase with potential applications to improve the viability of the process. In this work, we have studied the kinetics of this process using a silica-supported nickel catalyst in a packed bed reactor. In order to ensure the intrinsic kinetic regime, the effects of external and mass transfer on the overall kinetics were examined at relevant reaction conditions. The external mass transfer was found to affect the kinetics at 500 ⁰C and a space velocity of 80 h–1. The internal mass transfer was found to not limit the kinetics when a catalyst particle size in the range of 1000-2000 µm was used. Within the intrinsic kinetic regime, we found that the reaction order with respect to methane is in the range of 0.77-0.94, the activation energy is 110 kJ mol–1 and the rate determining step is the dissociation of the first C-H bond. In addition, the kinetics of the catalyst deactivation follows a first-order behavior with respect to the activity of the catalyst, with an activation energy of 125 kJ mol–1. At the end of the study, a mathematical model for the best-fit model was found using MATLAB. With the whole set of data, the best fit is obtained with a Langmuir-Hinshelwood type rate law.

Non-oxidative dehydrogenation of hydrocarbons is an attractive alternative route for the production of CO- and CO2-free hydrogen. It will satisfy a major requirement for successful utilization of polymer electrolyte membrane (PEM) fuel cells (< 10 ppm CO) and sequestering carbon as a potentially valuable by-product, carbon nanotubes (CNTs). Due to the deposition of carbon on the surface of catalyst particles during the reaction, catalyst performance, life-time, and purification of the generated carbon product, are significant issues to solve in order to make the process practically feasible. The scope of this thesis includes: the development of novel Fe, Ni, and Fe-Ni catalysts supported on a Mg(Al)O support to achieve improved catalytic performance with easily-purified CNTs; evaluation of catalysts for ethane/methane dehydrogenation at moderate reaction temperatures; and study of activation and deactivation mechanisms by a variety of characterization techniques including TEM, HRTEM, XRD, Mössbauer spectroscopy, and x-ray absorption fine structure (XAFS) spectroscopy. The Mg(Al)O support was prepared by calcination of synthetic MgAl-hydrotalcite with a Mg to Al ratio of 5. The catalysts were prepared either by conventional incipient wetness method or by a novel nanoparticle impregnation method, where the monodisperse catalyst nanoparticles were prepared in advance by thermal decomposition of a metal-organic complex in an organic-phase solution and then dispersed onto the Mg(Al)O support. Dehydrogenation of undiluted methane was conducted in a fix-bed plug-flow reactor. Before reaction, the catalysts were activated by reduction in hydrogen. Fe-based catalysts exhibit a higher hydrogen yield at temperature above 600ºC compared with monometallic Ni catalyst. FeNi-9 nm/Mg(Al)O, Fe-10 nm/Mg(Al)O and Fe-5 nm/ Mg(Al)O nanoparticle catalysts show much improved performance and longer life-times compared with the corresponding FeNi IW/Mg(Al)O and Fe IW/Mg(Al)O catalysts prepared by incipient wetness. 10 nm is the optimum particle size for methane dehydrogenation. Addition of Ni to Fe forming a bimetallic FeNi alloy catalyst enhances the catalytic performance at the temperatures below 650ºC. Metallic Fe, Ni, FeNi alloy and Fe-Ni-C alloy, unstable iron carbide are all catalytically active components. Catalysts deactivation is due to the carbon encapsulation. The carbon products are in the form of stack-cone CNTs (SCNTs) and multi-walled CNTs (MWNTs), depending on the reaction temperature and catalyst composition. The growth of CNTs follows a tip growth mechanism and the purity of cleaned CNTs is more than 99.5%.