Advanced Oxide Catalysts for Selective Hydrogenation Reactions
Final Report Abstract
Inspired by work published in literature, we designed and carried out experiments and theoretical investigations to better understand the role of ceria as a heterogeneous catalyst for the hydrogenation of alkenes and alkynes to alkanes and alkenes. In order to get closer to a fundamental understanding we combined surface science studies on single crystalline samples with those on powder samples (Chinese Partner Group). The former allowed us, by combining a number of different experimental techniques, to prove the strong influence of oxygen vacancies on the interaction of hydrogen from the gasphase with the solid surface, by comparing stoichiometric and reduced, non-stoichiometric CeO2(111) surfaces. It has been demonstrated, that non-stoichiometric ceria interacts with hydrogen by forming hydroxyl species at the surface, and by getting oxidized (Ce3+ - Ce4+) via the formation of hydride species underneath the surface. It was possible through theoretical calculations to demonstrate, that, indeed, the energetics favor such a reaction route. Based on those findings work on powder samples were started in the partner group and it was jointly demonstrated that the same phenomena also apply to those samples. It became clear, that, although, the surface hydride formation is the kinetically favorable process at relatively low temperatures, the resulting surface hydride may diffuse into the bulk region and be stabilized therein. At higher temperatures, surface hydroxyls can react to produce water and create additional oxygen vacancies, increasing its concentration, which then controls the H2/CeO2 interaction. The results demonstrate a large diversity of reaction pathways, which have to be taken into account for a better understanding of the reactivity of ceria-based catalysts in a hydrogen-rich atmosphere. In addition to the interaction of hydrogen with ceria we also studied water adsorption and the interaction with hydrocarbons with single crystalline stoichiometric and non-stoichiometric samples. Extensive studies on reactivity have been carried out on powder samples by the partner group, and the obtained results with the model systems turned out to allow for a mechanistic understanding of the observed reactions.
Publications
- Toward an Understanding of Selective Alkyne Hydrogenation on Ceria: On the Impact of O Vacancies on H2 Interaction with CeO2(111). J. Am. Chem. Soc., 139, 17608-17616, 2017
K. Werner, X. Weng, F. Calaza, M. Sterrer, Th. Kropp, J. Paier, J. Sauer, M. Wilde, K. Fukutani, S. Shaikhutdinov, H.-J. Freund
(See online at https://doi.org/10.1021/jacs.7b10021) - An in situ DRIFTS mechanistic study of CeO2-catalyzed acetylene semihydrogenation reaction. PhysChemChemPhys, 20, 9659-9670, 2018
Tian Cao, Rui You, Xuanyu Zhang, Shilong Chen, Dan Li, Zhenhua Zhang and Weixin Huang
(See online at https://doi.org/10.1039/C8CP00668G) - Synthesis in a glovebox: Utilizing surface oxygen vacancies to enhance the atomic dispersion of palladium on ceria for carbon monoxide oxidation and propane combustion. ACS Applied Nano Materials, 1, 4988-4997, 2018
Rui You, Zhaorui Li, Tian Cao, Bing Nan, Rui Si, and Weixin Huang
(See online at https://doi.org/10.1021/acsanm.8b01116) - Molecular beam/infrared reflection- absorption spectroscopy apparatus for probing hetero-geneously catalyzed reactions on functionalized and nanostructured model surfaces. Rev. Sc. Instrum., 90, 053903, 2019
S. Attia, E.J. Spadafora, J. Hartmann, H.-J. Freund, S. Schauermann
(See online at https://doi.org/10.1063/1.5093487) - Oxidation of Reduced Ceria by Incorporation of Hydrogen. Angew. Chem. Int. Ed., 58, 14686-14693, 2019
Z. Li, K. Werner, K. Qian, R. You, A. Plucienik, A. Jia, L. Wu, L. Zhang, H. Pan, H. Kuhlenbeck, S. Shaikhutdinov, W. Huang, H.-J. Freund
(See online at https://doi.org/10.1002/anie.201907117) - Spectroscopic study of microstructure-reducibility relation of CexZr1-xO2 solid solutions. Appl. Surf. Sci. 467-468, 361-369, 2019
Huizhi Bao, Kun Qian, Xiaoqi Chen, Jun Fang, Weixin Huang
(See online at https://doi.org/10.1016/j.apsusc.2018.10.168) - Morphology-dependent CeO2 catalysis in acetylene semihydrogenation reaction. Appl. Sur. Sci., 501, 144120, 2020
Tian Cao, Rui You, Zhaorui Li, Xuanyu Zhang, Dan Li, Shilong Chen, Zhenhua Zhang, Weixin Huang
(See online at https://doi.org/10.1016/j.apsusc.2019.144120) - Water-Assisted Homolytic Dissociation of Propyne on Reduced Ceria Surface. Angew. Chem. Int. Ed., 59, 6150-6154, 2020
J.-Q. Zhong, Z.-K. Han, K. Werner, X.-Y. Li, Y. Gao, S. Shaikhutdinov, H.-J. Freund
(See online at https://doi.org/10.1002/anie.201914271) - Electronic Structure of Reduced CeO2(111) surfaces interacting with Hydrogen as Revealed through Electron Energy Loss Spectroscopy in Comparison with Theoretical Investigations. J. Electron. Spectrosc. Related Phenom., 2021
J. Paier, C. J. Nelin, P. Bagus, A. Plucienik, H. Kuhlenbeck, H.-J. Freund
(See online at https://doi.org/10.1016/j.elspec.2021.147088) - Interaction of Hydrogen with Ceria: Hydroxylation, Reduction, and Hydride Formation on the Surface and in the Bulk. Chem. Eur. J., 27, 5268, 2021
Z. Li, K. Werner, L. Chen, A. Jia, K. Qian, J.-Q. Zhong, R. You, L. Wu, L. Zhang, H. Pan, X.-P. Wu, X.-Q. Gong, S. Shaikhutdinov, W. Huang, H.-J. Freund
(See online at https://doi.org/10.1002/chem.202005374)
