Thermo-catalytic decomposition (TCD) decarbonizes methane, producing solid carbon and “blue” hydrogen. Since active sites are linked to nanostructure, connections between kinetic rates, active sites and nanostructure comprise the objectives of this study. As hypothesis, autocatalytic nanostructure can be formed and perpetuated under TCD conditions, thereby renewing active sites and maintaining catalytic activity. In support, a few recent studies have using C2 or C3 hydrocarbons have demonstrated steady TCD rates suggesting rate control via reaction conditions and/or catalyst selection. Yet the deposited carbon was not characterized for nanostructure or active sites. Moreover, despite observed deactivation of nearly all carbon catalysts tested in TCD of CH4, connection between active sites and activity has not been made. In the present study TCD deposition rates are measured using a microreactor equipped with GC, along with methane conversion, reaction selectivity, activation energy and active sites. A CVD reactor is used for gravimetric carbon yield and complementary active site measurement. Nanostructure is characterized by custom image analysis algorithms applied to HRTEM data while active sites are quantified by combination of oxygen chemisorption-TPD and separately, XPS, the latter resolving chemisorbed oxygen groups. Crystallite structure is measured by XRD, Reactive gases include natural gas components, mixtures representing natural gas (containing C2 and C3 components), and natural gas mixtures doped with acetylene or an aromatic such as toluene to gauge effects of preceding gas-phase pyrolysis. Hydrogen is included as an additive to the natural gas components and their mixture. Autocatalytic activity is gauged against model catalysts. With rates as a function of active sites, with active sites in turn correlated with nanostructure, relationships will be developed between nanostructure and TCD rate. Ultimately simplified global and detailed kinetic models will be developed using experimental input.

Thermo-catalytic decomposition of methane: Connecting active sites, nanostructure and rates

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