EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Technologies for exhaust gas treatment in combustion processes are diverse. A major focus in the development of novel catalysts lies on cost reduction by lowering the precious metal content while maintaining the catalytic activity, e.g. by using transition metal oxides. Such porous materials with integrated catalytically active compounds for heterogeneous catalysis play a crucial role in current research. The costly and energy-consuming step of applying an active component to the support material can be circumvented by co-precipitation of active component and support material in a one-step synthesis. For this purpose, Prussian blue (PB) was co-precipitated next to its analogues (PBA) and subsequently calcined in this work. The main advantages are the highest possible homogeneity of transition metal and iron species due to the co-existence of both species on a molecular level, and the simultaneous formation of a hierarchical pore system.

Synthesis of Prussian blue analogues and subsequent calcination

By precipitating PBA next to a stoichiometrically defined amount of PB and subsequently calcination, a phase-pure spinel is obtained. Spinels are temperature-stable catalysts and supports in one material and are therefore particularly suitable for exhaust gas treatment. The aim of this study is to generate and maintain a hierarchical pore system during the synthesis and subsequent calcination to increase the catalytic activity in CO-oxidation experiments. This is achieved by using organic solvents during precipitation, and by protecting the pore systems with temperature-stable, water-soluble salts that can be leached out after calcination. First studies using DMF as capping agent and saturated K$_2$SO$_4$-solution as protecting reagent decreased the T90 temperature by 150 °C (from 378 °C to 223 °C). The phase composition, crystallinity, porosity, and stability of the obtained materials are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen sorption and mercury intrusion.