Global CO2 emissions from energy consumption are steadily increasing every year, and the demand for green alternatives to fossil fuel feedstocks is high. Fortunately, the focus on sustainable energy development strategies has never been greater. In the chemical industry, heterogeneous catalysts are used to increase the rate of chemical reactions. Using a catalyst often makes a chemical process more environmentally friendly as the required temperatures and pressures are less severe. However, the catalysts often suffer from deactivation due to the often detrimental reaction conditions.
The aim of this dissertation is to develop novel heterogeneous catalysts with high stability in chemical reactions at elevated temperatures or at deactivating reaction conditions. Here, heterogeneous catalysts were prepared by encapsulating active metals in engineered nanoporous structures. Deactivation of catalysts may be caused by sintering of the active metals at high temperatures, which means that the active metals agglomerate together, leaving less active surface area available for catalysis. In addition, deactivation may be caused by leaching of the active metals from the catalysts, which means that parts of the active metals are lost. Encapsulation of catalysts in various modified nanostructures was performed in order to investigate the resulting stability in chemical reactions. Here, the porosity of the nanostructured materials was modified to obtain different average pore sizes. The average pore sizes were designed to confine the active metals and therefore prevent them from sintering or leaching. Thermally stable heterogeneous catalysts were prepared from metal-organic frameworks used as sacrificial metal precursors. Additionally, non-leaching heterogeneous catalysts were prepared by metal impregnation of nano-engineered porous materials. The use of metal-organic frameworks as sacrificial metal precursors was found to hold great potential in the design of thermally stable catalysts with controlled properties. Moreover, the use of encapsulated active metals in nanostructures prepared by impregnation revealed promising results that can be used to design future non-leaching heterogeneous catalysts.
In summary, this dissertation describes the advantages and disadvantages of encapsulating active metals in nanostructured materials for the design of stable heterogeneous catalysts. This dissertation offers promising tools to increase the stability of future novel heterogeneous catalysts.