(668h) Kinetics of Catalytic Methane Pyrolysis for CO2-Free Hydrogen Production and Carbon Nanotube Synthesis over Co/Mo-MgO

Industrial methods of hydrogen production, which include steam methane reforming, water gas shift, and coal gasification, produce hydrogen for approximately $5 per kilogram. The U.S. DOE aims to reduce the cost of clean hydrogen production to just $1 per kilogram within the next decade. Catalytic methane pyrolysis in a fluidized bed is our proposed method of working towards this goal, as it avoids the costs associated with CO₂ capture and storage while producing carbon nanotubes, which may be sold to offset the cost of the clean hydrogen. Here we report the kinetics and mechanism responsible for methane conversion over a highly effective and reusable catalyst of cobalt, molybdenum, and magnesium oxide. This catalyst was designed to specifically foster carbon nanotube growth by a base-growth mechanism, which ensures metal particles are not incorporated inside the nanotube during growth. This facilitates potential intermittent removal of the nanotubes from the catalyst for industrial practicality.

In this presentation we present current findings on our Co/Mo-MgO catalyst which has achieved hydrogen production as fast as 0.9 mol H₂ g_cat^-1 hr^-1. This corresponds to a nanotube yield of 17 g_CNT/g_cat during a scalable three-hour reaction when operated at atmospheric pressure of methane. The catalyst is compared to Fe/Mo-MgO and Ni/Mo-MgO to show that cobalt achieves superior rates and deactivates more slowly than alternative metals. The role of catalyst deactivation via particle encapsulation is contrasted with relative sintering rates of metal particles within a carbide matrix to explain the variations in performance vs. time on stream between these catalysts. Then, deeper kinetic analysis will be shared in which the partial pressure of methane and hydrogen is varied during nanotube synthesis to decouple the kinetic relevance of methane activation vs. surface flux during both the initial carbon nucleation and steady state nanotube production.