Methane activation and selective hydrogenation on sub-nanometer-sized clusters

• Applicants: Privatdozent Dr. Friedrich Esch; Professor Dr. Ulrich Heiz
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: since 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 288470007

This renewal proposal focuses on the activation of small organic molecules by metal and metal oxide cluster catalysts, supported on oxides of different acidity and reducibility. The overarching aim is a fundamental understanding of how to steer activity and selectivity by tuning intrinsic properties of the cluster-assembled material: charge density at the active site, steric constraints and reactant coverage at reduced dimensions. We tackle two prominent and catalytically relevant examples where we aim at manipulating this particular chemistry at the active site of the cluster in a precise way: 1) selective hydrogenation of unsaturated aldehydes, i.e. controlling the chemoselectivity between two functional groups (C=C and C=O); 2) methane activation for the synthesis of higher hydrocarbons, i.e. chemoselectivity towards C-C coupling versus decomposition. The formulation of overarching concepts beyond single case studies requires atomically precise cluster samples and a complete set of complementary experimental approaches to obtain information on reactivity, stability and dynamics, adsorption geometry and morphology, oxidation state and local work function, to mention the most important ones. To this purpose, we extend our experimental portfolio of integral reactivity techniques (thermal desorption and reaction; pulsed molecular beam reactive scattering) and spectroscopies (XPS, UPS, MIES, AES, FTIR) by local scanning probe methods. In particular, we apply Scanning Tunneling Microscopy (STM) for characterization of morphology, dispersion and electronic structure of the supported clusters, FastSTM with up to video frequency time resolution for studying their in-situ dynamics, and Kelvin Probe Force Microscopy (KPFM) to compare the local work function on single clusters. The novelty of this project lies in the comprehensive understanding of the influence of intrinsic cluster-assembled material-properties on the selectivity in two reactions central for contemporary catalysis. This approach becomes possible through the complementary expertise and instrumentation of the two project partners, linking local and integral techniques at perfection. In addition, the potential of knowledge transfer of gas phase reactivity screening to supported cluster catalysis is evaluated, with implications in rational catalyst development.

• DFG Programme: Research Grants