Heterogeneous catalysts - operando experiments
Most chemical products on the market see a catalyst at some point during their production, in order to achieve high turnover with high selectivity and at comparably low temperatures. In general, heterogeneous catalysts are solid materials with high surface area that are capable to break bonds of adsorbed reactants. The reactions of gaseous or liquid reactants take place at the interface – at so called ‘active sites’. The structure of these active sites is often unknown, although the structural details and their long-term stability are of utmost importance for high-performance industrial catalysts.
Frequently, nanoparticles of metals and metal oxides like nickel and iron oxides act as catalytic species supported on porous solids like aluminium or titanium oxides, as well as graphitic supports.
High-energy X-rays are ideally suited to penetrate model reactors and we can watch the structural changes of the heterogeneous catalyst as the catalysis takes place. We employ powder X-ray diffraction (PXRD) coupled with pair distribution function (PDF) analysis as non-invasive probes in order to follow phase transformations, particle growth, catalyst deactivation, the occurrence of internal strain or the breathing of particles upon gas adsorption at gas-solid interfaces. Time resolutions of sub-seconds can be achieved.
Further, the nanoparticles, respectively active sites interact with the support materials as well as the reaction media. By careful difference-PDF analysis, i.e. subtraction of the support from the catalyst PDF data, we are able to shed insight into both restructuring of the catalytic support materials as well as the evolution of the catalyst species itself.
The structural insight with X-rays is combined with various analytical techniques for further characterization, such as thermogravimetric analysis (TGA), elemental analysis (ICP-OES, CHN), pore volumes (BET) or TEM, several of these carried out in collaboration with other work groups.
Our projects to this topic:
| Structure-activity correlation of methanation catalysts |
| Catalysts in the Fuel Science Center |
Please get in contact with us to join our team performing research via
- Catalyst characterization (TGA, XRD, PDF, etc.) in our laboratories
- Taking part in beamtimes on operando catalysis, or
- Data analysis of X-ray diffraction and pair distribution function data (commercial software with graphical user interface, Origin Pro, or python).
Publications:
Schönauer, Timon; Thomä, Sabrina L. J.; Kaiser, Leah; Zobel, Mirijam; Kempe, Rhett*: General synthesis of secondary alkyl amines via reductive alkylation of nitriles by aldehydes and ketones. Chem. Eur. J. (2020), 26. https://doi.org/10.1002/chem.202004755
Elfinger, Matthias; Schönauer, Timon; Thomä, Sabrina L. J.; Stäglich, Robert; Zobel, Mirijam; Senker, Jürgen; Drechsler, Markus; Kempe, Rhett*: Co Catalyzed Synthesis of Primary Amines via Reductive Amination employing Hydrogen under very mild Conditions. ChemSusChem (2021). https://doi.org/10.1002/cssc.202100553