Mixtures
of molten iron–sodium-potassium chloride salts
are found to be catalytic for methane pyrolysis. In a differential
bubble column reactor, the apparent activation energy of the molten
salt decreases from 301 kJ/mol for the eutectic NaCl-KCl to 171 kJ/mol
for 3 wt % of iron-added as FeCl3. The solid carbon produced
in the iron-containing salt mixture has a graphitic structure which
is distinct from the more disordered carbon produced in the iron-free
eutectic, suggesting a different solid carbon formation pathway. Results
from H–D exchange investigations are consistent with a different
reaction pathway for methane pyrolysis in the iron-containing NaCl-KCl
melt than in the melt without Fe. The activity of the salt mixture
was stable for over 50 h, producing molecular hydrogen and separable
solid carbon. It is likely that the activity is due to the presence
of Fe in molecular ions stabilized in the NaCl-KCl melt that facilitate
the C–H bond activation in methane.
A molten salt mixture containing
45 mol % KCl and 55 mol % CuCl2 was investigated as a catalyst
for the reaction of HCl with
O2 to produce Cl2. The HCl conversion for an
HCl:O2 molar feed ratio of 1:2 at 450 °C and a total
pressure of 1 atm was 80% at a residence time of less than 1 s in
a lab scale bubble column reactor. The equilibrium conversion at this
temperature and pressure is 84%. The catalyst system was found to
remain stable throughout a continuous 24-h experiment. The use of
a mixed transition metal/alkali metal molten salt catalyst for HCl
oxidation reduces the volatility of supported chlorides and may avoid
the mechanical stability limitations of solid catalysts caused by
volume changes between the halide and the oxide.
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