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Heterogeneous catalytic pyrolysis of hydrocarbons to produce CO2-free hydrogen and high-quality solid carbon have historically been stymied by issues related to catalyst deactivation by carbon formed during pyrolysis on the catalyst surface. In addition, a system that demonstrates sustained performance in terms of high conversion, high H2 yield, and high quality of produced carbon has remained elusive. Here, we propose and demonstrate a semi-continuous methane pyrolysis process to H2 and carbon nanotubes (CNTs) consisting of repeated pyrolysis and in situ (i.e., within the reactor) CNT dislodging by vigorous steam/argon fluidization. With this process, we demonstrate 10 process cycles with high H2 yield from CH4 and CNT dislodging in a fluidized-bed reactor with an Fe/θ-Al2O3 catalyst synthesized by an easily scalable incipient wetness impregnation process. We also identify and present opportunities for future catalyst and process development.
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•Proposition and demonstration of a semi-continuous pyrolysis process•Production of CO2-free H2 and carbon nanotubes from CH4 on a supported catalyst•Demonstration of in situ CNT dislodging for repeated catalyst use
Sun, Zhai, and Kim et al. present a methane pyrolysis catalyst to produce carbon nanotubes (CNTs) and propose and demonstrate a semi-continuous process that features in situ CNT dislodging so that the catalyst can be continuously cycled. The produced CNTs could offset the cost of H2 production in a commercialized process.