Controlling
the selectivity of products among CO, methane, and
methanol is a challenge in CO2 hydrogenation. Catalysts
with oxygen vacancies are helpful for CO2 activation, but
they exhibit poor CO selectivity as intermediates stabilized over
oxygen vacancies undergo deep hydrogenation to methanol and methane.
Here, we report the synthesis of a catalyst with isolated Co atoms
in ZrO2 that exhibits oxygen vacant sites near Co atoms
owing to charge imbalance between cations. The resulting catalytic
site effectively adsorbs CO2 and also achieves more than
95% CO selectivity during hydrogenation. The CO selectivity was independent
of other reaction parameters such as reaction pressure, space velocity,
and H2/CO2 ratio. Operando DRIFTS analysis showed
that CO2 was first hydrogenated to formate, which preferentially
decomposed to CO under the reaction condition instead of forming methanol.
Furthermore, the adsorption of CO on active sites was less favorable
than the adsorption of CO2, limiting its further hydrogenation
to methane. The synergy between Co and Zr was crucial for the generation
of oxygen vacancy and stabilization of formate species as an intermediate
for CO formation. This study shows the importance of strategic design
of atomic interface to control the selectivity of a specific product
from CO2 hydrogenation.
Synthesis of methanol with high selectivity and productivity through hydrogenation of CO2 is highly attractive. This work uses Rh doped In2O3 catalyst to achieve high methanol productivity of 1.0 gMeOH...
Partial
oxidation of methane (POM) is a potential technology to
increase the efficiency of synthesizing a mixture of CO and H2 called syngas, in comparison to steam reforming processes.
Recently, supported metals modified with Re have emerged as active
catalysts for POM. However, the role of Re in this reaction has been
unclear. Here, we demonstrate that the addition of Re to a Ru/Al2O3 catalyst changes the reaction mechanism. The
bimetallic catalyst oxidizes CH4 to mainly CO via formate.
After all of the O2 is used, steam reforming and reverse
water-gas shift take place to increase the yield of CO and H2. This is in contrast to Ru/Al2O3, which catalyzes
POM mostly by complete oxidation of CH4 to CO2 and H2O and subsequent reforming reactions. In the bimetallic
catalyst, the main role of Ru is to reduce Re species, and the reduced
Re species produces formate from CH4 and also accelerates
the steam reforming reaction. The dual roles of Re increase the total
catalytic performance. These results show that Re is a main player
rather than a simple promoter in the catalytic reaction.
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