To develop low-$$\hbox {CO}_2$$
CO
2
emission ferrous metallurgical process, $$\hbox {H}_2$$
H
2
-based ironmaking processes are being actively developed. Several technologies are being developed to provide a sufficient mass of $$\hbox {H}_2$$
H
2
in an environmentally friendly manner. One of such processes is “turquoise” $$\hbox {H}_2$$
H
2
, based on a natural gas pyrolysis such as $$\hbox {CH}_4$$
CH
4
(g) $$\rightarrow $$
→
2$$\hbox {H}_2$$
H
2
(g) + C(s), thereby minimizing $$\hbox {CO}_2$$
CO
2
emission. The reaction could be catalyzed using molten metals in a bubble column reactor. Therefore, the selection of the molten metal catalyst is important for enhancing the reaction efficiency and for minimizing the production cost. In the previous research of the present authors, a new methodology for the pyrolysis rate measurement was introduced by employing an electromagnetic levitation heating of catalytic molten metals followed by quadrupole mass spectrometer (QMS) analysis to assist in the selection of the catalyst metal. However, a potential source of error in this technique was identified. Therefore, two modifications of the methodology are reported in the present study: (1) changing the heating and feed gas supply patterns and (2) gas analysis technique from QMS to Gas Chromatography (GC). Accordingly, the reported pyrolysis rate of pure In, Ga, Bi, Sn, and Cu of the previous study was revised in the present study. It was revealed that Ga and In emitted non-negligible amounts of $$\hbox {H}_2$$
H
2
upon heating, even without the fuel gas ($$\hbox {CH}_4$$
CH
4
). This was regarded as a noise in the $$\hbox {H}_2$$
H
2
signal measured by GC. On the other hand, Cu, Sn, and Bi did not show the noticeable $$\hbox {H}_2$$
H
2
(noise). The modified method provides $$\hbox {H}_2$$
H
2
production rate by the pyrolysis, by separating the noise in the regime of the chemical reaction control at the surface of the molten metals. $$1^\text {st}$$
1
st
-order reaction was confirmed.
Graphical Abstract
