Area C: Analysis, Theory and Simulation

The static and dynamic electronic and geometric structure of multiprobe organometallic complexes in porous polymers

The aim is to investigate the influence of a mesoporous environment on catalyst properties aiming for rational development of improved molecular heterogeneous catalysts. These properties include the electronic structure and the mobility of the catalyst inside the pore. To this end we have selected a model complex equipped with a number of orthogonal spectroscopic handles. We will immobilize this probe molecule into porous polymer films with precisely known anchoring points as well as into structurally well-defined covalent organic frameworks. We will develop novel spectroscopic tools to determine the dynamic and static behavior of the probe molecule.

High resolution tomography of mesoscopic pore structures

The project aims at the high resolution analytical microscopy of mesoporous matrices as well as of the linkage and position of the active catalysts. To this end, correlative microcopy is suggested that combines the methods of electron microscopy with the single-atom analysis of atom probe tomography. Major methodical developments are required for the atom probe tomography. Filling of the pores with contrasting liquids, a subsequent cryo-preparation, cutting to nanometric needles by focused ion beams and the direct transfer of these samples between the dual beam microscope and the atom probe are the essential steps of the planned innovation.

Simulation of chemical reactivities 

The catalytic reactions investigated in the B-area will be studied. Rate constants of their chemical steps will be calculated using quantum chemical methods. The influence of the pore will be modeled by a QM/MM approach. This will also clarify possible geometric arrangements of the catalytic complex, reactants, products, linkers, and the solvent in the pore. Additionally, field desorption and fragmentation of molecules will be simulated to facilitate the interpretation of atom probe tomography measurements in C3. C4 will model the smallest length scale in this CRC and complement the other theory projects.

Atomistic and fluid-theoretical predictions of static and dynamic fluid properties in functionalized silica mesopores

Classical force field all-atom molecular simulations are applied to determine the multicomponent phase behavior and transport properties in mesoporous confined geometries. Special attention will be given to silica materials. Once established the pore models allow for a systematic investigation of the effect of pore size, shape, polarity of functional groups, type of solvent, temperature and pressure on the environment around catalytically active sites. From the simulations scale-bridging properties are extracted that are used to parametrize classical (molecular) density functional theory approaches and coarse-graining models.

A multi-scale simulation approach for optimizing molecular heterogeneous catalysis in confined geometries

We will investigate the role of structural, conformational details, as well as the dynamics and transport properties of the starting material (reactants) and products with immobilized catalysts within confined nanometer-sized geometries. From bottom-up we will study intermolecular interactions within the density-functional-theory approach. At larger scales we will quantify the transport of reactants and products in and out of confined spaces during the catalysis with a reactive or hybrid particle/lattice Boltzmann algorithm.

Using Immobilized Ru Hydride Complexes to Understand the Interaction of Molecular Heterogeneous Catalysts with the Pore Walls under Catalytic Conditions

Interaction of immobilized catalysts with pore walls, known as surface collapse (SC), causes loss of catalytic efficiency. The goal of this project is to measure the extent to which immobilized species interact with the pore walls under catalytically relevant conditions. We do this by immobilizing Ru hydrides in porous supports and examining their activity and selectivity during CO2 hydrogenation. SC results in a change in activity and selectivity, enabling the measurement of the amount of SC in various solvents and temperatures. These results will be important to prevent deactivation via surface collapse in all catalytic projects within the CRC.

X-ray absorption spectroscopy of molecular heterogeneous catalysts in mesoporous materials

X-ray analysis in project S1 will comprise of XANES, EXAFS, HERFD-XANES, vtc-XES, and ctc-XES measurements. These methods provide information about the oxidation state (XANES), local structural parameters around an X-ray absorbing metal center (EXAFS), the LUMO (HERFD-XANES) and HOMO (vtc-XES) states of the complexes under investigation and their spin state (ctc-XES) without the need for any translational symmetry. Using this hard X-ray bunch of methods in combination with theoretical calculations (project C4), all relevant information to understand the structure and working principle of molecular heterogeneous catalysts in projects B1-B3 in situ as well as in operando can be obtained.