EFCA - Programme Franco-Allemand : Catalyse Homogène et Hétérogène pour le Développement Durable (Environmentally Friendly homogeneous and heterogeneous Catalysis - EFC)

Activation of CO2 on ZnO surfaces and subsequent reactions with nucleophilic coadsorbates – ACTCO2

Activation of CO2 on ZnO surfaces and subsequent reactions with nucleophilic coadsorbates

Transforming carbon dioxide, a pollutant molecule but a valuable feedstock.

Interaction between CO2, zinc oxide (ZnO) and Cu/ZnO or Au/ZnO materials.

CO2 is a greenhouse gas responsible for global climate warming. It may be possible to limit its emission, to store it but also to use it to obtain high added value products. This last goal implies its activation to increase its reactivity towards other molecules and the use of heterogeneous catalysts that are solid materials able to increase the rate of a given chemical reaction. Different reactions can be considered as CO2 addition on organic molecules (alcohols, amines, epoxydes) or the reduction by dihydrogen to produce methanol. The system chosen for this study was zinc oxide (ZnO) based materials on which metals as copper or gold could be deposited, that were identified to be good candidates at least for methanol synthesis from CO/CO2/H2 gaseous mixtures. The main goal of the project was to study the adsorption of CO2 on these surfaces and to look for correlations between this behaviour and the catalytic performances. Another challenge was to prepare Cu/ZnO et Au/ZnO catalysts with very small copper or gold particles to optimize the adsorption and the catalytic processes.

The scientific approach included mainly three aspects:
• The study of the materials preparation.
Cu/ZnO and Au/ZnO (1 % wt% of metal) must be obtained with very small particle size. The synthesis routes tested were deposition-precipitation with urea and incipient wetness impregnation. In the case of copper a reduction step is necessary and the operating conditions have been carefully studied.
• The study of CO2 interaction with ZnO support and with Cu/ZnO et Au/ZnO.
First of all, the adsorption of CO2 on ZnO has been studied with techniques usually used in Surface Chemistry field such as Ultra High Vacuum Infra-Red spectroscopy and the results were correlated with the data obtained from ambient pressure Infra-Red Spectroscopy and CO2 chemisorption that are more familiar in heterogeneous catalysis studies. Then some results concerning the influence of the metallic deposition on the ZnO surface have been obtained.
• Catalytic properties evaluation. This last step of the project is still under consideration.

By nature, this bilateral project between two german teams and a French one has initiated an international partnership that will be maintained in the future.
The main results obtained are scientific and are given below:
- Preparation of very small Cu (4 nm) and Au (2 nm) particles on ZnO support
- Revealing the formation of an alloy, Cu3Zn, in the Cu/ZnO system and investigation of its formation conditions.
- Infra-Red spectroscopy identification of the carbonates species formed on ZnO surface and insight on their stability.
- Highlighting the influence of the oxidative nature of the pretreatment gas, used to activate the materials, on their CO2 adsorption capacity.

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Five scientific articles were written during this project.
- Study of Cu/ZnO synthesis. Following the formation of Cu3Zn alloy
S. Derrouiche, H. Lauron-Pernot, C. Louis, Chem. Mater, 24 (2012) 2282
- Identification by infrared spectroscopy of carbonate species formed upon CO2 adsorption on ZnO in ultra high vacuum conditions.
H. Noei, C. Wöll, M. Muhler, Y. Wang, J. Phys. Chem. C, 115 (2011) 908
- Study of the co-interaction of CO and CO2 with ZnO surface by infrared spectroscopy in ultra high vacuum conditions.
H. Noei, C. Wöll, M. Muhler, Y. Wang, Applied catalysis A: General, 391 (2011) 31
- Study of the interaction of H2 with ZnO surface by infrared spectroscopy in ultra high vacuum conditions
H. Noei, H. Qiu, Y. Wang, M. Muhler, C. Wöll, Chem. Phys. Chem. 11 (2010) 3604
- Review on the mechanisms proposed for the reaction of CO2 on epoxydes, which is one of the CO2 valorization route among the most studied.
G. Laugel, C. Carvalho Rocha, P. Massiani, T. Onfroy, F. Launay accepté dans Advanced Chemistry Letters.

The activation of CO2 to produce high-value products is one of the most important topics in catalysis. In heterogeneous catalysis all the already known industrial processes of CO2 activation need high temperatures and/or pressures, effective heterogeneous catalysts to achieve the activation of CO2 are hardly available. In this species present on the single crystal and on the oxide particle surfaces. With regard to an industrial application the corresponding CO2 activation reactions will be studied and their fabrication as well as their loading with metals will be optimized using industrialstyle fixed-bed reactors.

Project coordinator

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

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Beginning and duration of the scientific project: - 0 Months

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