Methane was decomposed to hydrogen and carbon nanotubes (CNTs)
by microwave plasma, using Fe/Si catalyst activated by biased (—150
V) hydrogen plasma for various treatment times. Upon exposure to biased
hydrogen plasma, the catalyst surface becomes lumpy within 1 min, coheres
between 5 and 10 min and forms particles after 20 min. The methane conversion
increased up to 93% over the treatment time of 5 min. The hydrogen yield showed
as similar tendency as the methane conversion and kept 83% at treatment time of 5
min. The treatment time up to 1 min increased the amount of deposited carbon,
and after treatment time of 5 min it dropped; then again after treatment time
of 20 min, it increased to reach a maximum value of 22 gc/gcat.
Deposited carbon was found to be consisted of carbon nanotubes. It grew
vertically on the catalyst surface and reached a maximum length of 30.7 nm
after treatment time of 10 min. Multiple types of CNTs were present, and the CNT
diameters decreased with increasing plasma treatment time.
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