Heterogeneous Oxidation Catalysis in the Liquid Phase

A08: Probing the Dynamics of Thermal Catalysis by Vibrational Modulation Excitation Spectroscopy

Prof. Dr. Martin Muhler • Dr. Sharif Najafishirtari

The characterization of catalysts and their dynamics under operando conditions is of great interest. However, this is quite challenging especially when the reaction medium involves complex reactants and products which can have different interactions with the catalyst surface. The complexity increases even further when solvent molecules are added to the system, i.e., by changing from gas-phase to liquid-phase catalysis, which can compete for adsorption and further blur the spectroscopic information about the catalyst surface under reaction conditions.

In view of this, we aim to apply a sophisticated experimental and mathematical approach, known as modulation excitation spectroscopy with phase-sensitive detection (MES-PSD), which can provide an unprecedented insight into the processes on the surface and in the bulk which are dynamically responding to the changes in the reaction atmosphere and thus establishing reliable structure-performance correlations. To this aim, the catalysts from the C area will be systematically studied in continuous-flow mode reactors by operando diffusive reflectance infrared Fourier transform (DRIFT) and Raman spectroscopy while the feed is modulated between the reaction mixture and an inert/solvent medium. DRIFTS will be limited to gas-phase reactions, but the effects of solvents and their interactions will be studied by co-feeding them at different concentrations along with the reactants using specially designed dosing units. On the other hand, Raman will be used both in gas and liquid media. The results will be interpreted in conjunction with several standard characterization methods as well as theoretical calculations available in the A and B areas. Additionally, other mathematical titration tools, such as multivariate curve resolution alternating least squares (MCR-ALS), will be also applied on the transient time-resolved operando spectroscopic data to extract kinetic information about the pure species/states present/evolving within the catalysts and the reaction medium along with their concentration profiles.

(Figure: Schematic of the microreactor to be used for operando liquid phase MES experiments).