Today’s workhorses in industrial catalysis are zeolites: crystalline, inorganic porous frameworks with tetrahedral connectivity. The big success of zeolites is their robustness, well defined pore distribution and dimensions and the option to vary their chemical composition. Traditionally, zeolites are porous (alumino)silicates, but they can also contain hetero-elements in the framework.

Herein, we will focus on the introduction of germanium (Ge) or aluminum (Al) as hetero-element into zeolites. Recently, the introduction of Ge led to the discovery of zeolites with pores larger than the 12-ring pores. These zeolites are particularly interesting as catalyst materials or for separation involving large feedstock molecules. The increased flexibility of O-Ge-O angles and bond-lengths allows larger ring sizes and also stabilises small cage structures like double four- or three-rings (D4R and D3R), which are often part of the large pores encountered in the large pore zeolites. Although the importance of the introduction of the hetero atoms is clear, their precise distribution is the zeolite framework remains very uncertain. In Figure (a) an example of a Ge-containing zeolite is depicted: the red spheres refer to oxygen, the blue to silicon and the purple ones to germanium; investigating the position of the latter forms the topic of this master thesis.

This distribution will be investigated using nuclear magnetic resonance (NMR) spectroscopy. With NMR the magnetic properties of atomic nuclei can be investigated. A magnetic field is used to split the energy levels of the nuclear spin levels (see Figure (b)). Electromagnetic energy can be absorbed and re-emitted at certain resonance frequencies. The best known application of this technique is Magnetic Resonance Imaging (MRI) for medical applications. Since the development of magic angle spinning for solid-state NMR, this technique has played an important role in zeolite characterisation, but it has only recently reached the required high resolution for structure determination. The focus of this master thesis is the computation of NMR properties using ab initio electronic structure methods.

The calculation of solid-state NMR properties is still challenging, since a plane wave-pseudo-potential implementation of Density Functional Theory (DFT) is required. Recent theoretical developments and implementations in solid-state codes (such as VASP) provide a great opportunity to advance in ab initio modeling of solid-state NMR. The obtained results can then be combined with experimental data to reveal detailed structural information on the investigated systems.

Goal The goal of this thesis is to compute NMR properties of metal-exchanged zeolites using plane wave-based electronic structure methods. After a literature survey, the student will get familiar with performing ab initio simulations on nanoporous zeolite materials using a plane wave-based code. The first step will be the optimization of the geometrical structure. In a next step, hetero atoms will be introduced in the framework and various properties, both energetic and NMR based, will be computed.

This topic focusses on the simulation of NMR based spectroscopic properties of zeolitic materials which are used in petrochemical processes. The interested student will learn a lot about the possibilities of molecular modeling and NMR spectroscopy. Moreover, this insight will be applied on an interesting class of materials. This master thesis hence combines a more theoretical/fundamental study and insight with practical simulations on realistic systems. The needed software is available, and the interested student will need to get familiar with it. However, no programming is required. This topic contributes to current research activities at the Center for Molecular Modeling and intensive coaching will be provided. Depending on the main interest of the student, the focus can lie on the theoretical part – i.e. performing ab initio simulations and computing NMR based properties - or on the application part – i.e. elucidating the possibilities of NMR spectroscopy for structure characterization of new classes of catalyst materials.