Robert Gleissner

Doctoral project

Operando investigation of Cu/ZnO model catalysts for methanol synthesis and CO2 activation

The synthesis of methanol is an important process for future strategies in developing a sustainable carbon cycle on our planet, including solar hydrogen storage in liquid hydrogen carriers. During methanol synthesis CO or CO2 is reacting with H2 to methanol (CH3OH) in the presence of an Al2O3 supported Cu / ZnO nanoparticle catalyst at temperatures between 200°C and 300°C and pressures in the 50-100 bar regime. The role of ZnO for the activity and selectivity of this catalyst for methanol synthesis was debated in the past and only recently it was proposed, that Zn atoms decorate specific defects on the surface of the Cu nanoparticles, thereby lifting kinetic barriers for fast CO2 hydrogenation [1,2,3]. Under varying water vapor and hydrogen gas compositions Cu nanoparticle shape changes were observed by ambient pressure transmission electron microscopy [4]. However, there is a lack of atomistic experimental insight into the structure of the Cu / ZnO nanoparticles under operando methanol synthesis conditions, which is related on the one hand to the structural complexity of a real powder catalyst by the size and shape distribution of the metal nanoparticles. On the other hand it is connected to the harsh high pressure / elevated temperature conditions, which excludes many experimental techniques. Open questions concern the nanoscale behavior of the Cu – Zn – ZnO system under methanol synthesis conditions, especially the role of Zn dissolution in Cu nanoparticles and surface segregation phenomena, as well as segregation and adsorption induced Cu nanoparticle shape changes. The goal of the project is to investigate Cu / ZnO model catalysts under conditions relevant for methanol synthesis by a combination of operando x-ray diffraction, imaging and spectroscopy of the reaction intermediates [5,6,7].

Model catalysts will be prepared by Cu nanoparticle deposition via thermal evaporation on ZnO single crystal surfaces and membranes. In this way model catalysts can be prepared, which consist of epitaxial Cu nanoparticles with defined orientation and controlled shape, as well as tailored defect structure. As the group at DESY demonstrated, synchrotron radiation based x-ray diffraction is a very powerful tool to characterize the size, shape and atomic structure as well as defects of such model catalysts under gas exposure and reaction conditions [8,9]. Surface sensitive x-ray diffraction methods are especially suited to address the surface structure of nanoparticles in the size regime of 10 nm and to correlate structural information with model catalyst performance. 

 

[1] M. Behrens, F. Studt, I. Kasatkin, S. Kühl, M. Hävecker, F. Abild-Pedersen, S. Zander, F. Girgsdies, P. Kurr, B.-L. Kniep, M. Tovar, R. W. Fischer, J. K. Nørskov, R. Schlögl, Science 336 18 893 (2012).

[2] S. Kattel et al., Science 355, 1296–1299 (2017)

[3] S. Kuld, et al., Science 20 MAY 2016 • VOL 352 ISSUE 6288 969

[4] Poul L. Hansen et al., Science 295, 2053 (2002);

[5] A. Stierle, J. Gustafson, E. Lundgren in "Operando Research in Heterogeneous Catalysis" Springer Series in Chemical Physics, Vol. 114 (2017)

[6] Franklin (Feng) Tao*,†,‡ and Peter A. Crozier*, Chem. Rev. 2016, 116, 3487−3539

[7] P. Amann, A. Nielsson, Rev. Sci. Inst. 90 (10), 103102, 2019

[8] P. Nolte, A. Stierle, et al., Science 321, 1654-1658 (2008).

[9] U. Hejral, A. Stierle, et al., Nature Communications 7, 10964 (2016)

 

Publications

Operando reaction cell for high energy surface sensitive x-ray diffraction and reflectometry, 2022, (https://doi.org/10.1063/5.0098893)

Copper Nanoparticles with High Index Facets on Basal and Vicinal ZnO Surfaces, 2021, (https://pubs.acs.org/doi/full/10.1021/acs.jpcc.1c08008)

Interaction of Water with Graphene/Ir(111) Studied by Vibrational Spectroscopy, 2019, (DOI: 10.1021/acs.langmuir.9b01205)

Monitoring the Interaction of CO with Graphene Supported Ir Clusters by Vibrational Spectroscopy and Density Functional Theory Calculations, 2018, (DOI: 10.1021/acs.jpcc.7b10845)