Oxidation State Drives CO2 Hydrogenation Over Co3O4 Catalyst: Molecular Level Understanding
Anastasiia Efremova, András Sápi, Imre Szenti, Ákos Kukovecz, Zoltán Kónya
Department of Applied and Environmental Chemistry, University of Szeged, H-6720, Hungary
Abstract: Noble metals especially in nanoscale have proved to show excellent catalytic properties in many important processes . However, they are expensive materials which amount is limited, hence, search for new solutions is of great interest nowadays. While using supported noble metals catalysts is a promising approach, metal oxide supports themselves can exhibit good activity, remaining more economically feasible.
In this work we have tested different types of Co3O4: synthetically prepared mesoporous m-Co3O4 (BET surface area 95 m2/g) and commercially purchased from Merck c-Co3O4 (BET surface area 15 m2/g) in CO2 hydrogenation reaction applying different reduction temperatures (273-673K), followed by applying HR-TEM, XRD, XPS, GC and DRIFTS techniques for characterization and catalytic activity tests measurements. M-Co3O4 is generally more active compared to c-Co3O4. After pre-treatment different distribution of cobalt species registered by XPS were similar, however, after CO2 hydrogenation reaction the surface of m-Co3O4 is mostly in oxidized form and that of c-Co3O4 is totally reduced. This implies that reaction follows different pathways over the same type catalyst. This was further supported by DRIFTS results.
1% 5 nm Pt nanoparticles were loaded onto the Co3O4 in order to check competitiveness of the catalysts. Pt nanoparticles increased the CO2 consumption rate of c-Co3O4 by 1.8 times and that of m-Co3O4 by 1.26 times. However, Pt nanoparticles did not change the reaction route and the IR features developed during reaction remained the same as for free standing supports.
Results obtained in this work emphasize the importance of metal oxide states in the given catalytic process. Investigating behaviour of these species enables the design of new catalytic systems, reducing the trial-and-error nature of these experiments.
 Thenner, S. R.; Anderson, G. M.; Pedro, H. C. J. Mater. Chem. A. 2019, 11, 5857–5874.