Dr. Kevin Kähler - Catalytic Technology

Dr. Kevin Kähler
Leiter der Gruppe Catalytic Technology
Abteilung Heterogene Reaktionen

Vita

Chemie Studium
Ruhr Universität Bochum (2001-2006)
PhD / PostdocRuhr Universität Bochum (Laboratory of Industrial chemistry, Prof. M. Muhler) (2006-2013)
PostdocMPI CEC (Heterogeneous Reactions, Prof. R. Schlögl) (2014)
GruppenleiterMPI CEC 'Catalytic Technology' (seit 2015)

Publikationen

Ausgewählte Publikationen

  • M. Bukhtiyarova, T. Lunkenbein, K. Kähler, R. Schlögl, „Methanol Synthesis from Industrial CO2 Sources: a Contribution to Chemical Energy Conversion”, Catal. Lett. 147 (2017) 416-427.
  • K.F. Ortega, D. Rein, C. Lüttmann, J. Heese, F. Özcan, M. Heidelmann, J. Folke, K. Kähler, R. Schlögl, M. Behrens, „Ammonia Decomposition and Synthesis over Multinary Magnesio-ferrites: Promotional Effect of Ga on Fe Catalysts for the Decomposition Reaction”, ChemCatChem 9 (2017) 659-671.
  • K. Mette, S. Kühl, A. Tarasov, M.G. Willinger, J. Kröhnert, S. Wrabetz, A. Trunschke, M. Scherzer, F. Girgsdies, H. Düdder, K. Kähler, K. Friedel Ortega, M. Muhler, R. Schlögl, M. Behrens, T. Lunkenbein, „High-Temperature Stable Ni Nanoparticles for the Dry Reforming of Methane“, ACS Catal. 6 (2016) 7238-7248.
  • K. Mette, S. Kühl, A. Tarasov, H. Düdder, K. Kähler, M. Muhler, R. Schlögl, M. Behrens, „Redox dynamics of Ni catalysts in CO2 reforming of methane”, Catal. Today 242 (2015) 101-110.
  • H. Düdder, K. Kähler, B. Krause, K. Mette, S. Kühl, M. Behrens, V. Scherer, M. Muhler, „The role of  carbonaceous deposits in the activity and stability of Ni-based catalysts applied in the dry reforming of methane“, Catal. Sci. Technol. 4 (2014) 3317-3328.
  • K. Mette, S. Kühl, H. Düdder, K. Kähler, A. Tarasov, M. Muhler, M. Behrens, „Stable Performance of Ni Catalysts in Dry Reforming of Methane at High Temperatures for the Efficient Conversion of CO2 into Syngas“, ChemCatChem 6 (2014) 100-104.
  • M.C. Holz, K. Kähler, K. Tölle, A.C. Van Veen, M. Muhler, „Gas phase oxidation of 2-propanol over Au/TiO2catalysts to probe metal-support interactions“, Phys. Status Solidi B 250 (2013) 1094-1106.
  • K. Kähler, M.C. Holz, M. Rohe, A.C. Van Veen, M. Muhler, „Methanol oxidation as probe reaction for active sites in Au/ZnO and Au/TiO2 catalysts“, J. Catal. 299 (2013) 162-170.
  • K. Kähler, T. Franzke, M. Muhler, „Thermochemical CO2 Activation“, in: Chemical Energy Storage, hg. von R. Schlögl, De Gruyter, Berlin/Boston, 2013.
  • K. Kähler, M.C. Holz, M. Rohe, J. Strunk, M. Muhler, „Probing the Reactivity of ZnO and Au/ZnO Nanoparticles by Methanol Adsorption: A TPD and DRIFTS Study“, ChemPhysChem 11 (2010) 2521-2529.
  • J. Strunk, K. Kähler, X. Xia, M. Comotti, F. Schüth, T. Reinecke, M. Muhler, „Au/ZnO as catalyst for methanol synthesis: The role of oxygen vacancies“, Appl. Catal. A 359 (2009) 121–128.
  • J. Strunk, K. Kähler, X. Xia, M. Muhler, „The surface chemistry of ZnO nanoparticles applied as heterogeneous catalysts in methanol synthesis“, Surf. Sci. 603 (2009) 1776–1783.

Vollständige Publikationsliste

Gruppenmitglieder

Wissenschaftliche Mitarbeiter

  • Dr. Holger Ruland
  • Dr. Elham Safaei Takhtehfouladi
  • Dr. Jorge Iván Salazar Gómez

Postdocs

  • Dr. Hua Fan
  • Dr. David Klein

PhD Studenten

  • Jan Markus Folke
  • Omar Alberto Mayorga Vielma
  • Denise Rein

Labor

  • Christian Klucken
  • Agnes Stoer
  • Johanna Taing
  • Christian Weimann

Catalytic technology group

In the catalytic technology group heterogeneously catalyzed reactions are investigated. Catalysis is of major importance for an energy-effective and sustainable conversion of reactants as it lowers the activation barrier of a chemical reaction by changing its reaction mechanism. In heterogeneous catalysis, usually, the catalyst is a solid, whereas the reactants exist in the surrounding fluid phase.  Deeper understanding of catalytic processes can help to improve the efficiency of reactions and, therefore, help to save resources and lower the overall energy demand.

In the catalytic technology group reactions are focused, which are of interest in the scope of energy conversion and storage. Nowadays, solar, wind, and hydro energy are often regarded as sustainable energy sources and can help to solve the shortage of hydro carbon-based energy sources in an environmentally friendly way. Electro-catalytic hydrogen production is investigated in the institute and is often discussed as key technology to store the fluctuatingly appearing renewable energies. Numerous techniques to store the hydrogen have been suggested including the generation of ammonia and methanol, which are investigated in the catalytic technology group. Both substances offer the advantage of high hydrogen contents and are easy to store as they are condensable [1].

Analysis of exhaust gases of steel mill plants

Besides the electro-catalytic generated hydrogen different other chemical source materials can play an important role in chemical industry for the future. In the catalytic technology group the capability of the usage of industrial exhaust gases as potential hydrogen, carbon and/or nitrogen sources for methanol and ammonia synthesis is investigated. An extensive analysis of real exhaust gases from steel mill plants is performed for all kind of trace components including metals, sulfur-, nitrogen-, and chlorine-containing compounds, polycyclic aromatic hydrocarbons, as well as benzene, toluene, ethylbenzene, and xylene (BTEX-aromatics), and for many other gaseous components. Off-line exhaust gas analysis from blast furnace gas, coke oven gas, and converter gas were already performed. As the complex composition of the exhaust gases depends on the production conditions as well as the raw materials and is, therefore, time dependent, a detailed continuous analysis over longer time periods is mandatory. That is why in the catalytic technology group two mobile containers (a Lab-container and a Supply-container) were designed and constructed within the Project HügaProp (German: Hüttengasproperties), which was funded by the Federal Ministry of Education and Research (German: Bundesministerium für Bildung und Forschung BMBF, Förderkennzeichen 03EK3546). The Lab-container is a mobile high-end gas analysis laboratory housed in a container to analyze the steel mill gases directly on-site. It is equipped with a new generation PTR-SRI-QiTOF-MS for high performance analysis and reactor set-ups for catalytic testing in methanol. The exhaust gas analysis of the steel mill plants will be performed within the project Carbon2Chem in the subproject L0, which is also funded by the Federal Ministry of Education and Research (German: Bundesministerium für Bildung und Forschung BMBF, Förderkennzeichen 03EK3038C).

Methanol synthesis

Nowadays methanol is produced from feed gas mixtures containing CO, CO2, and H2 in a conventional, continuously performed process using a Cu/ZnO/Al2O3 catalyst. As the Cu/ZnO/Al2O3 system is also active in the hydrogenation of pure CO2 without CO in the feed gas, the methanol synthesis starting from CO2/H2 mixtures is a promising candidate to help to stabilize the CO2 level of the atmosphere. Simultaneously, a re-incorporation of the green-house gas CO2 into the value added chain of the industrial chemistry can be achieved as methanol is the most important alcohol with respect to its production volume and numerous applications. A future sustainable and environmental friendly production route from exhaust gases renders a deeper understanding of the CO2 hydrogenation and an expansion of the known parameter space of a Cu-based catalyst important. The usage of CO2-rich feed gases, possibly without any CO at all, and dynamic operation conditions pose typical challenges for such a process and are investigated in the catalytic technology group. The influence of parameters such as pressure, temperature and space velocity is investigated with respect to the reaction performance to help to establish a fundament for the usage of exhaust gases of e.g. steel mill plants [2].

In the catalytic technology group reactivity studies of the CO2 hydrogenation are performed within the project Carbon2Chem in the subproject L2 (ProMeOH - Methanolsynthese aus Hüttengasen), which is funded by the Federal Ministry of Education and Research (BMBF, Förderkennzeichen 03EK3039D). The reactor applied houses sufficient catalyst to determine the productivity by volumetric analysis of condensate and high-precision GC-MS product analysis. Furthermore, the influence of impurities of the exhaust gases on the catalyst activity and stability is investigated. To find out to which extent gas purification is necessary, systematic reactivity and stability studies in methanol synthesis have been started. Feed gases consist of COx, hydrogen, and additionally trace components, which are usually found in the exhaust gases, like benzene as a representative of BTEX-aromatics.

Ammonia synthesis

Ammonia synthesis represents an additional way to store hydrogen produced with renewable energy sources. It is well known that ammonia synthesis is a structure sensitive reaction [3]. Nevertheless, there is still a large pressure and material gap between activity data at industrial relevant conditions and surface science approaches. That is why it was planned to investigate a systematic series of catalysts with different surface structures and to correlate their activity to their structure. For this purpose the catalytic technology group investigates the activity and stability of alternative Fe-based catalyst systems in a kinetic flow set-up [4]. Another key point in the alternative catalyst preparation routes is the circumvention of the high-temperature melting process of the iron oxide precursor. Such a “green” synthesis allows studying the interplay of morphology and promoter chemistry in the formation of the active iron species.

A special reactor was constructed allowing the disassembly of the catalyst inside a glove box without contact to the ambient for ex-situ characterization methods. This may help to elucidate whether surface, subsurface, or bulk nitride species are generated during the reaction, as the active phase of the Fe-based catalyst under industrially used conditions is still unclear [5]. The very low conversion in ammonia synthesis at mbar pressure precludes direct in-situ analysis and the extreme air-sensitivity of the activated catalysts represents a major hurdle in getting insight into the chemistry of the active form of ammonia iron.

Oxidative dehydrogenation of ethyl benzene

For the investigations of the oxidative dehydrogenation (ODH) of ethylbenzene forming styrene, a kinetic flow set-up was constructed in the catalytic technology group. ODH is an energy saving candidate for the synthesis of styrene. Additionally, ODH can also be employed for the characterization of carbon materials, which are produced in the “carbon synthesis and application” group in the institute. Carbon materials are active in the ODH reaction and are, therefore, interesting and cost-effective materials [6]. (Di)carbonyl surface functional groups that can be modified by additional dopants such as nitrogen are assigned to be the active sites [7]. An extensive characterization and correlation to activity data can shed light into this assignment. If the structure-activity relation is identified, the ODH of ethyl benzene can outstandingly supplement the existing characterization methods and can be incorporated perfectly in the master plan of the institute.

References

[1] Jensen, J. O.; Vestbø, A. P.; Li, Q.; Bjerrum, N. J., J. Alloys Compd. (2007) 446-447, 723.

[2] Bukhtiyarova, M., Lunkenbein, T., Kähler, K., Schlögl, R., Catal. Lett. (2017) DOI: 10.1007/s10562-016-1960-x.

[3] Schlögl, R., Ammonia Synthesis. In Handbook of Heterogeneous Catalysis, 2 ed.; Ertl, G.; Knözinger, H.; Schüth, F.; Weitkamp, J., Eds. Weinheim (2008).

[4] Ortega, K.F., Rein, D., Lüttmann,, C., Heese, J., Özcan, F., Heidelmann, M., Folke, J., Kähler, K.,  Schlögl, R., Behrens, M., ChemCatChem, DOI: 10.1002/cctc.201601355.

[5] Kandemir, T., Schuster, M.E.,  Senyshyn, A., Behrens, M., Schlögl, R., Angew. Chem. Int. Ed. (2013) 52, 12723.

[6] Delgado, J., Chen, X., Frank, B., Su, D.S. , Schlögl, R., Catal. Today (2012) 186, 93.

[7] Rinaldi, A., Zhang, J., Frank, B., Su, D.S., Hamid, S.B.A., Schlögl, R. ChemSusChem (2010) 3, 254.

Projects