Heterogeneous Oxidation Catalysis in the Liquid Phase

A07: Oxidation Catalysis on Solvated Transition Metal Oxide Surfaces: From Well-Defined Models to Powder Beds

Prof. Dr. Malte Behrens • Prof. Dr. Swetlana Schauermann

Heterogeneously catalyzed oxidation of alcohols and olefins will be addressed in this project with a focus on the role of solvent molecules. Solvated surfaces and their reactivity will be studied with a unique combination of methods ranging from investigations at the atomistic-level on model catalytic surfaces using a surface science approach to the investigations of their powder counterparts under technologically relevant conditions using kinetic steady state information, which will be obtained both by co-dosing of the solvent and by true liquid phase catalysis. The project thus will bridge the materials and pressure gaps for specific research questions related to catalytic turnover at solvated (mixed) metal oxide surfaces, which are motivated by the results of the CRC’s Comparative Study of the first funding period.

The aim is to elaborate fundamental insight into the effect of solvent molecules on the reaction mechanism of alcohol and olefin oxidation to link this atomistic knowledge with the performance under technically relevant conditions studied simultaneously on powder catalysts. The materials under study will be (modified) cobalt oxide surfaces and the project’s starting point is the aerobic oxidation of 2-propanol in the presence of water addressing the specific beneficial role of water molecules beyond mere competitive adsorption established in the first funding period by the observation of a lower activation energy in wet feeds. The work will be extended to other reaction systems of relevance to the CRC, especially to the usage of acetonitrile as solvent for hydrophobic substates.

In the surface science part, the reaction mechanism and kinetics will be addressed by a combination of in operando IRAS, multi-molecular beam techniques and STM applied on well-defined models surfaces that allow for unravelling the underlying surface processes and the structure/reactivity relationships. Complementary, the catalytic activity and selectivity will be addressed in the applied catalysis part by a detailed analysis of the steady state kinetics in two types of flow-through reactors in the presence of first gaseous and finally liquid solvents on the real powder catalysts. In both parts of the project, identical oxidation reactions will be explored, comprising alcohols (isopropanol and benzylalcohol) and olefins (cyclohexene) in presence of aqueous or non-aqueous (acetonitrile) solvents. In addition to Co3O4, also doped variants with iron, vanadium and manganese as well as mixed oxide with lanthanum (perovskites) will be investigated as catalysts, which will be prepared as well-defined ultrathin films and obtained as powders from Research Area C.

The outcome of the proposed research will be fully integrated into the progress on identification of reaction mechanisms and active sites obtained in the CRC, and holds a great potential for developing new concepts towards rational-based design of surfaces with tailor-made catalytic properties in oxidation catalysis in the third funding period.

(Figure: Schematic representation of the research rationale, and the interplay and complementarity of the Behrens and Schauermann parts of A07).