CO2 hydrogenation
to methanol can play an important
role in meeting the sustainability goals of the chemical industry.
In this study, we investigated in detail the role of the Cu–CeO2 interactions for methanol synthesis, emphasizing the role
of the copper surface and interface sites between copper and ceria
for the hydrogenation of CO2 and CO. A combined CO2–N2O titration approach was developed to
quantify the exposed metallic copper sites and ceria oxygen vacancies
in reduced Cu/CeO2 catalysts. Extensive characterization
shows that copper dispersion is strongly enhanced by strong Cu–CeO2 interactions in comparison to Cu/SiO2. CO2 hydrogenation activity data show that the Cu/CeO2 catalysts displayed higher methanol selectivity compared to a reference
Cu/SiO2 catalyst. The improved methanol selectivity stems
from inhibition of the reverse water-gas-shift activity. The role
of CO in CO2-to-methanol conversion was studied by steady-state
and transient cofeeding activity measurements together with (quasi)
in situ characterization (TPH, XPS, SSITKA, and IR spectroscopy).
The Cu–CeO2 interface provides active sites for
the direct hydrogenation of CO to methanol via a formyl intermediate.
Cofeeding of small amounts of CO2 to a CO/H2 mixture poisons these interfacial sites due to the formation of
carbonate-like species. Methanol synthesis proceeds mainly via CO2 hydrogenation in which the metallic Cu surface provides the
active sites.
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