Prof. Dr. Martin Muhler

 Prof. Dr. Martin Muhler

NBCF 04/691     0234 32 28754

SFB 558    CES    IFCS    SurMat    Solvation   OCMOL   CeNIDE   vfch

Heterogeneous catalysts are essential for the majority of all chemical processes in industry. In addition, they find numerous applications in refineries and in energy conversion, and they help to protect the environment. Nevertheless, their discovery and their optimization has often been based on trial and error, and there are only a few cases, in which a complete understanding on the atomic level was achieved.

The Laboratory of Industrial Chemistry performs fundamental research in the area of heterogeneous catalysis and aims to develop catalysts based on mechanistic insight. The scientific challenge is the elucidation of the reactions on the atomic level and their interplay with the complex surface chemistry of heterogeneous catalysts, which usually consist of many phases and components, often present as nanoparticles or as X-ray amorphous layers.

The examined reactions belong to industrial redox chemistry.  Reduction catalysis comprises methanol synthesis, Fischer-Tropsch synthesis, or the synthesis of higher alcohols. Oxidation catalysis focuses on the selective oxidation of propene and methanol, the oxidative dehydrogenation of hydrocarbons, or the selective oxidation of alcohols in the gas phase and in the liquid phase. Recently, we entered the fields of electrocatalysis and heterogeneous photocatalysis. Liquid-phase oxidation and electrocatalysis require a deeper understanding of solvation-related phenomena.

For the synthesis of catalysts  a large repertoire of methods is available including chemical vapor deposition, spray drying and precipitation performed in a cascade of micromixers. In recent years the catalytic growth and surface modification of multiwalled carbon nanotubes (CNTs) has become a major topic due to the numerous applications of CNTs in electrocatalysis.  All the necessary routine techniques for catalyst characterization are available with a strong focus on sorption techniques.

For improving the catalysts we first of all study steady-state kinetics. Numerous continuously operated flow set-ups with online analytics are available, which allow to screen the parameter space efficiently under full computer control using LabVIEW. The role of the various elementary steps is investigated by applying transient kinetic methods such as temperature-programmed reactor operation, dosing pulses and concentration steps, and using isotopes including SSITKA. For these methods we strongly rely on fast online mass spectrometry. In addition, we try to gain as much spectroscopic information as possible using mainly FTIR and photoelectron spectroscopy. Recently, static and dynamic microcalorimetry have been developed into versatile tools to probe the surface properties quantitatively. 

Our research contributes to the Collaborative Research Center SFB 558 "Metal-substrate interactions in heterogeneous catalysis", the Research Departments Interfacial Systems Chemistry (IFSC), Materials Research, and Plasma, the Center for Electrochemical Sciences (CES), all at the Ruhr-University Bochum, and to the Center for Nanointegration Duisburg-Essen (CeNIDE).

Selected publications
  1. Stearate-based Cu colloids in methanol synthesis: structrual changes driven by strong metal-support interactions, S. Schimpf, A. Rittermeier, X. Zhang, Z. Li, M. Spasova, M. van den Berg, M. Farle, Y. Wang, R. Fischer, M. Muhler, ChemCatChem, 2010, 2, 214-222

  2. Electrocatalytic activity and stability of nitrogen-containing carbon nanotubes in the oxygen reduction reaction, S. Kundu, T. C. Nagaiah, W. Xia, Y. Wang, S. van Dommele, J. H. Bitter, M. Santa, G. Grundmeier, M. Bron, W. Schuhmann, M. Muhler, J. Phys. Chem. C, 2009, 113, 14302-14310

  3. A highly efficient gas-phase route for the oxygen-functionalization of carbon nanotubes based on nitric acid vapor, W. Xia, C. Jin, S. Kundu, M. Muhler, Carbon, 2009, 47, 919-922

  4. High surface area ZnO nanoparticles via a novel continuous precipitation route, S. Kaluza, M. K. Schröter, R. Naumann d'Alnoncourt, T. Reinecke, M. Muhler, Adv. Funct. Mater., 2008, 18, 3670-3677

  5. Consistent approach to adsorption thermodynamics on heterogeneous surfaces using different empirical energy distribution models, X. Xia, S. Litvinov, M. Muhler, Langmuir, 2006, 22, 8063-8070

  6. The influence of strongly reducing conditions on strong metal-support interactions in Cu/ZnO catalysts used for methanol synthesis, R. Naumann d' Alnoncourt, X. Xia, J. Strunk, E. Löffler, O. Hinrichsen, M. Muhler, Phys. Chem. Chem. Phys., 2006, 8, 1556-1565

  7. On the mechanism of the oxidative amination of benzene with ammonia to aniline over NiO/ZrO2 as cataloreactant, N. Hoffmann, M. Muhler, Catal. Lett., 2005, 155-159

  8. The two-step chemical vapor deposition of Pd(allyl)Cp as an atom-efficient route to synthesize highly dispersed palladium nanoparticles on carbon nanofibers, C. Liang, W. Xia, H. Soltani-Ahmadi, O. F.-K. Schlüter, R. A. Fischer, M. Muhler, Chem. Commun, 2005, 282-284

  9. On the nature of the active state of supported ruthenium catalysts used for the oxidation of carbon monoxide: Steady-state and transient kinetics combined with in situ Infrared Spectroscopy, J. Aßmann, V. Narkhede, L. Khodeir, E. Löffler, O. Hinrichsen, A. Birkner, H. Over, M. Muhler, J. Phys. Chem. B, 108, 2004, 14634-14642

  10. Mechanistic studies on the oxidative dehydrogenation of methanol over polycrystalline silver using the temporal-analysis-of-products approach, A. C. van Veen, O. Hinrichsen, M. Muhler, J. Catal., 2002, 209, 501-514

  11. The ammonia synthesis catalyst of the next generation: barium-promoted ruthenium, H. Bielawa, O. Hinrichsen, A. Birkner, M. Muhler, Angew. Chemie Int. Ed., 2001, 40, 1061-1063

  12. On the role of monomeric vanadyl species in toluene adsorption and oxidation on V2O5/TiO2 catalysts: a Raman and in situ DRIFTS study, S. Besselmann, E. Löffler, M. Muhler, J. Mol. Catal. A: Chem. 2000, 162 , 393-403