The_Catalyst_Review_December_2023 - 18

These workers began by varying
several reaction parameters,
including temperature, pressure,
reaction time, and catalyst loading,
to identify conditions favorable
for the hydrogenation of K2
to methane over the 5%Ru/Al2
CO3
O3
catalyst in an aqueous solution
followed by optimization of the
system in terms of methane
productivity (Figure 1 a and b). An
X-ray diffraction (XRD) spectrum of
the catalyst shows that the Ru/Al2
Figure 1. Optimization of methane productivity with the 5%Ru/Al2
10 mL H2O, [a] X hours, 300 mg 5%Ru/Al2
bar H2
O3, 225°C, 50 bar H2, [b] X mg 5%Ru/Al2
, 6 hours. Yields calculated by gas chromatography are within ±5%.
O3. Conditions: 10 mmol K2
O3
CO3
, 225°C, 50
,
O3
is likely deactivated throughout the
reaction through the formation of
RuO2
, limiting the amount of active
metal, ruthenium, in the system
(2a). Scanning electron microscope
(SEM) images of the 5% Ru/Al2
O3
catalyst before and after the reaction
suggest a morphology change
within the catalyst throughout the
reaction. Three catalyst loadings were
then evaluated to further improve
the methane productivity of the
system, with the highest productivity
obtained with 50 mg catalyst, an
amount then chosen for further study.
Variations of the reaction conditions
using 50 mg of 5%Ru/Al2
O3
catalyst
were then studied (Figure 2). For
comparison, the first bar (a) displays
the results with some favorable
conditions determined above, i.e., 60
bar H2
Al2
H2
O3, 10 mmol K2
, 6 hours, 250°C, 50 mg 5%Ru/
, and 10 mL
CO3
O. Keeping the same conditions
but lengthening the reaction time
from 6 to 24 h, the methane yield
increased significantly to 100%,
resulting in a quantitative conversion
of the 10 mmol K2
CO3 present in the
reaction mixture.
Natural sources of CO2
were also
investigated for the conversion
to methane. Both seashells and
eggshells were converted to methane
in moderate yields, with seashells
converting to methane in similar
yields to pure calcium carbonate,
36.3% vs 44%, respectively. Direct
air capture of CO2
with KOH and
conversion of the obtained K2
CH4
CO3
to
in quantitative yields was also
demonstrated. In this case, however,
the catalyst's activity towards
carbonate hydrogenation decreased
severely over several capture/
hydrogenation cycles. Koch CJ,
Suhail Z, Goeppert A, et al. (2023)
ChemCatChem doi.org/10.1002/
cctc.202300877
18
The Catalyst Review
December 2023
Figure 2. Variations on the reaction conditions for methane productivity. Conditions: [a] 60 bar
H2
O3, 10 mmol K2
O.
CO3
, 10 mL H2
O3, 10 mmol K2
CO3, 10 mL H2O, [c] 60 bar H2
O, [b] 60 bar H2, 250°C, 24
, 250°C, 6 hours, 50 mg
O3, 10 mmol CO2, 10 mL H2
, 250°C, 6 hours, 50 mg 5%Ru/Al2
hours, 50 mg 5%Ru/Al2
5%Ru/Al2
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