Complexity of a Co3O4 System under Ambient-Pressure CO2 Methanation: Influence of Bulk and Surface Properties on the Catalytic Performance

Anastasiia Efremova,Imre Szenti,Ákos Kukovecz,András Sápi,Gyula Halasi,Gábor Varga,Juan Gómez-Pérez,Zoltán Kónya,T Rajkumar,Ákos Szamosvölgyi,János Kiss,Kornélia Baán

doi:10.1021/acs.jpcc.0c09717

Anastasiia Efremova, Imre Szenti + Show 10 more

Open Access

https://doi.org/10.1021/acs.jpcc.0c09717

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Abstract

Although using supported noble-metal catalysts for CO2 hydrogenation is an effective solution due to their excellent catalytic properties, metal oxide supports themselves can exhibit good activity being more economically feasible. This work focuses on investigating the complexity of the Co3O4 system during the CO2 methanation reaction, which is usually accompanied by the formation of unstable dispersions of cobalt oxide and metallic Co. Herein, we have tested different types of Co3O4: synthetically prepared mesoporous m-Co3O4 (BET surface area, 95 m2/g) and commercial c-Co3O4 (BET surface area, 15 m2/g; purchased from Merck) in the CO2 methanation reaction under different reduction temperatures (273–673 K). The reduction temperature was adjusted to 573 K for both the catalysts to reach the optimal Co/cobalt oxide ratio and consequently the best catalytic performance. m-Co3O4 is more active (CO2 conversion 95%) and stable at higher temperatures compared to c-Co3O4 (CO2 conversion 63%) due to its morphology-induced ∼66 times higher surface basicity. DRIFTS results showed differences in the detected surface species: formate was observed on m-Co3O4 and was proven to contribute to the total methane formation. It was revealed that in CO2 methanation reaction, both bulk and surface properties such as morphology, cobalt oxidation states, acid–base properties, and presence of defect sites directly affect the catalytic performance and reaction mechanism. Furthermore, 1% 5 nm Pt nanoparticles were loaded onto the Co3O4s to check the competitiveness of the catalysts. This study evidences on a cheap noble-metal-free catalyst for CO2 methanation consisting of m-Co3O4 with competitive activity and ∼100% CH4 selectivity.

Highlights

One of the currently most important ecological concerns is associated with the growing concentration of CO2 in the atmosphere, which occurs due to the intense utilization of carbon-rich fossil fuels such as coal, oil, and natural gas
The morphology of Co3O4 samples was studied by transmission electron microscopy (TEM)
Even though metallic Co is commonly acknowledged to serve as the active site in CO2 methanation reaction for Co-based catalysts,[10,11,16,66] the results reported in this work support that for CO2 methanation, both cobalt oxide phase and metallic phase are important

Summary

Introduction

One of the currently most important ecological concerns is associated with the growing concentration of CO2 in the atmosphere, which occurs due to the intense utilization of carbon-rich fossil fuels such as coal, oil, and natural gas. The increase of atmospheric CO2 contributes to a series of environmental problems such as global warming and ocean acidification.[1,2] Catalytic hydrogenation of CO2 using a sustainable H2 source reduces CO2 emissions and produces valuable fuels and chemicals.[3] CO2 is a stable molecule that requires an energy-demanding catalyst for its activation.[4]. Noble-metal−metal-oxide catalysts have received much attention methanation.[5−7] owing to their extensive applications in CO2 In these systems, metal oxides aid for the dispersion of noble metals and affect catalytic activities due to the presence of strong metal−support interaction.[8,9].

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