Milada Teubnerová

• Metal-organic frameworks (MOFs) have gained increasing attention in the last four decades due to their versatility and unique properties. They are often used as catalysts because they combine advantageous properties of both heterogeneous and homogeneous catalysts. Noble metals are very active in catalysis, but they are expensive, sometimes toxic to the environment and very rare. Therefore, the demand for the substitution of noble metals by commonly available metals such as iron or cobalt is of interest. The complexity and versatility of MOF materials is further enhanced by the use of mixed-linker and mixed-metal approaches or post-synthetic modification reactions. The aim of this PhD project was to synthesize and characterize MOF-based catalysts which contain Co and Fe and to test the resulting materials in the liquid phase oxidation reaction of alcohols. In the first part of this work, mixed-metal CPO-27(Co,Fe) with three different metal ratios and two different spatial distributions were prepared. The spatial distributions of the metals were either statistically distributed or a core-shell orientation. The resulting catalysts were characterized by powder X-ray diffraction, thermogravimetric analysis and ICP-OES analysis. The results confirmed that the catalysts were highly porous, corresponded to the CPO 27 structure and that the amounts of metals were close to the desired ratios. The materials were then tested in oxidation reactions of benzyl alcohol and 1-phenylethanol. For the parameter optimization, the highly active monometallic CPO-27(Co) catalyst was used and parameters such as temperature and the amount of catalyst, substrate or oxidant (air) were investigated. Bimetallic CPO-27(Co,Fe) catalysts were then tested with the optimized parameters and both conversion and selectivity were compared to the monometallic CPO 27(Co) reference. In general, the rare and expensive cobalt can be partially replaced by cheap but inactive iron without affecting the catalytic activity and in some cases, the distribution of the metals in the MOF lattice have an effect on the catalytic performance. In the second part of this work, the previously synthesized CPO-27(Co,Fe) catalysts were thermally decomposed in an inert atmosphere to obtain metal species which are encapsulated in a porous carbonaceous matrix via the so called MOF-mediated synthesis. The decomposition was expected to result in unique materials that could not be synthesized by any other route. The resulting materials were characterized by powder X-ray diffraction, N2 physisorption and ICP-OES analysis. The characterization revealed differences between materials prepared from statistically distributed and core-shell-structured CPO-27(Co,Fe). These catalysts were also tested in the oxidation of benzyl alcohol and compared not only within this series but also with the CPO-27 precursors, showing that in some cases the thermally decomposed materials were even more catalytically active than their MOF precursors. In the last part of this thesis, Co,Fe DUT-5-based catalysts with core-shell structure and statistical distribution, respectively, were synthesized. The first step was to prepare a DUT-5-based framework. For the statistically distributed material, 4,4'-biphenyldicarboxylate, 2,2' bipyridine-5,5'-dicarboxylate and 2-amino-4,4'-biphenyldicarboxylate linkers were mixed with an aluminum salt precursor. The 2,2'-bipyridine-5,5'-dicarboxylate linkers were then used to directly immobilize cobalt ions. The amine-functionalized linkers were post-synthetically modified with salicylaldehyde and the resulting chelating groups were finally used for the immobilization of iron ions. The core-shell backbone consisted of 4,4'-biphenyldicarboxylate and 2,2'-bipyridine-5,5'-dicarboxylate in the core. The first shell contained only unfunctionalized 4,4' biphenyldicarboxylate and the outer shell consisted of a mixture of 2 amino-4,4'-biphenyldicarboxylate and 4,4'-biphenyldicarboxylate linkers. The post-synthetic reactions were then performed analogously to the statistically distributed materials: (1) cobalt immobilization at the bipyridine linkers, (2) insertion of chelating groups at the amine linkers and (3) iron immobilization. All materials were thoroughly characterized after each synthesis step using powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, N2 physisorption and ICP-OES analysis. The linker ratios were calculated by 1H NMR of diluted samples. The results confirmed the formation of a porous material with a DUT-5 structure, but the spatial distribution could not be confirmed unambiguously by the methods used. Both materials were tested, together with a monometallic DUT-5 BPyDC(Co) reference, in oxidation reactions cinnamyl alcohol. The results showed significant differences between the statistically distributed and core-shell catalysts, providing evidence for the difference in spatial orientations and the symergistic effects of the two metals. In summary, novel MOF materials containing Co and Fe were synthesized, characterized and tested in oxidation reactions of primary and secondary alcohols under aerobic conditions. The results confirmed that in some cases a part of rare cobalt could be replaced by cheap and widely available iron without decreasing the catalytic activity and selectivity. In addition, the spatial distribution of the metals can have a direct and massive influence on the catalytic properties and therefore, a thorough characterization is a very important part of the synthesis process.