Metal–organic frameworks (MOFs) are ordered arrays of polytopic organic ligands, commonly called linkers, which interconnect metal-based inorganic building units via coordination bonds. The highly precise assembly of well defined building blocks into extended 3-D networks, known as reticular chemistry, has allowed researchers in this field to produce tens of thousands of different frameworks. As an obvious consequence of their unprecedented porosity and tunability, these versatile materials are continuously studied with various potential applications in mind. An important portion of MOF research has been invested in the interaction between molecules and the framework, aiming for applications such as gas storage and separation, as well as catalysis, drug delivery, heat exchange, and water harvesting.

MOFs are considered soft or flexible materials, a characteristic that includes structural dynamics or large amplitude deformations. This flexibility can usually be attributed to the framework’s topology and the degrees of freedom of some of its bonds. However, the linkers themselves may also have degrees of freedom allowing independent molecular dynamics, in particular in the form of rotation. This type of dynamics is particularly common in MOFs because their porous architectures often provide enough space for the rotation of a molecular fragment to occur. It is this type of dynamics that this thesis is centered on, starting from the fact that, although it is an intriguing phenomenon that occurs in MOFs, it has remained relatively unexplored.

Nevertheless, the past four years have seen an increase in researchers’ interest in rotational dynamics in MOFs. This may be due to two main reasons: First, linker rotation influences MOF properties, not only when guest molecule interactions are involved, but also in optical and mechanical properties. Development of our knowledge on linker rotation is therefore essential for a more complete understanding of these materials’ properties and how they may be modified to enhance a specific trait. Second, the exploitation of linkers’ rotational freedom could potentially lead to important technological advances. The latter category includes various innovative ideas, such as the design of ferroelectric MOFs by means of controllable dipolar rotors, or the realization of crystalline molecular machines able to produce useful work.

This dissertation is devoted to the attractive and rapidly developing field of
heterogeneous catalysts with isolated metal sites. The following research
questions served as the source of inspiration for it: • How to design a catalyst with isolated metal sites? • How to synthesize and develop a catalyst with isolated metal sites? • How to characterize a catalyst with isolated metal sites?
In the first part of this dissertation (Chapters 2-3) the route for design,
synthesis, characterization and further modification of heterogeneous
catalysts with isolated sites is described, using the development of a
catalyst for direct conversion of methane to methanol as an example. The
second part (Chapters 4-5) investigates the applicability of X-ray based
analysis techniques (primarily X-ray photoelectron spectroscopy (XPS) and
X-ray absorption spectroscopy (XAS)) for the characterization of such
catalysts

Membrane separation is an energy efficient technology with a small physical footprint in which the membrane is the core of process. Membranes need to be further developed to be specifically applied in the field of gas separation. The most challenging target in designing membranes is to improve the permeation and selectivity, simultaneously. This goal cannot be achieved without acquiring the knowledge of material science to tune the membrane material properties. This PhD thesis focusses on designing mixed matrix membranes (MMMs) by using a new class of crystalline materials known as metal organic frameworks (MOFs) as filler. In combination with polymers as continuous phase it was expected to improve both the processability and separation performance of this composite material in comparison with the polymer only. This work has been performed in the framework of the FP7-EU project M4CO2 ('MOF-based Mixed Matrix Membranes for energy efficient CO2 capture', grant agreement n° 608490). Therefore the focus in this thesis was on, but not limited to, membranes for the separation of CO2 from N2, as a model for stack gases in coal combustion ('post-combustion separation'). To this aim, the overall concept of this thesis is divided into three parts in which the most relevant aspects of design in mixed matrix membranes are carefully studied. Part I (Chapter 2) elucidated the influence of MOF pore structure and topology on the MMMs separation performance. In part II (Chapter 3 and 4) the effect of MOF morphology and polymer free volume is studied. Finally, part III (Chapter 5) reports a study on free-standing and thin supported MOF nanosheet based membranes by using industrially viable methods. The summary of each Chapter in this thesis is presented as follows...

Bottom-up approaches for the synthesis of nanostructured heterogeneous (electro-) catalysts, via the colloidal deposition route combined with nanostructured catalyst supports, have been investigated in this thesis. Colloidal gold nanoparticles have been selected as a case study in view of their promising catalytic properties for oxidation reactions, as well as their ability to convert carbon dioxide to carbon monoxide under electrocatalytic conditions. Benzyl alcohol aerobic oxidation was selected as a test reaction of choice to characterize the catalytic properties of the colloidal gold nanoparticles under investigation, in view of the extensive literature available on this topic. Furthermore, practical experience with this reaction and colloidal gold nanoparticles had already been gained in the Catalysis Engineering group, reflected by a previous publication involving dodecylamine-capped gold nanoparticles...

This thesis, Gas Adsorptive Separation through Microporous Materials, presents the research done on gas separation processes in the Catalysis Engineering team. This thesis intends to collect the knowledge and results of five years’ experimental research dealing with gas mixtures and microporous materials, but also with tubing, and setup maintenance and designing. This thesis contains a first introduction chapter, four research chapters (based on journal publications) and this last summarizing chapter with an outlook about the field of adsorption regarding the thesis' results.

Formed from an organic linker and a metal salt cluster, Metal Organic Frameworks (MOFs) are highly crystalline materials with a large surface area, pore size and pore volume. Some of these MOFs show a step-wise water adsorption behaviour. This would make them suitable for seasonal thermal heat storage through water adsorption, due to their high stability in a moist air environment and a relatively large adsorption capacity. This thesis is dedicated to modelling MIL-101(Cr), MIL-100(Fe), Aluminium fumarate, MOF-841(Zr), CAU-10(Al)-H, MIL-125(Ti)-NH2, MIL-160(Al) and CPO-27(Ni). The adsorption capacity was tested using two situations with a different set of temperatures. From these MOFs, three of the better performing MOFs were eventually tested, to measure the water adsorption energy density. With this data, the expected needed storage volume of the MOF was estimated, where the best MOF was chosen.

Electrocatalytic reduction of CO2 is one possibility to solve the electrical energy storage problem and decrease the amount of CO2. Copper is the only metal that has been reported to produce hydrocarbons in the electrochemical CO2 reduction at ambient pressure and temperature. External parameters (potential, temperature and electrolyte), copper catalyst morphology and purity and newly designed carbon-based electrodes were investigated. The highest Faraday efficiency towards hydrocarbons at 22°C was obtained at a fixed potential of -2.50 V vs. Ag/AgCl reference electrode. The best electrolyte solution is 0.1 M KHCO3. Methane is the dominant product. FE towards ethylene maximizes at -2.25 V. Up to 40°C, the total Faraday efficiency towards hydrocarbons is not influenced by temperature, but ethylene amount increases with increasing temperature. Above 40°C hardly any hydrocarbons are formed. Altering the surface structure of the copper catalyst by electrodeposition give different results for the electrocatalytic CO2 reduction. The rougher the surface, the less methane and the more ethylene was formed. The macroscopic smooth surfaces are related to the (001) orientation and a rough macroscopic surface is related to the (111) orientation. To increase the surface area, carbon-based catalyst supports (graphite plates, carbon nanofibers and carbon xerogels) were tested. They show promising results.