Relating extrusion as a method of bifunctional catalysts synthesis and their catalytic performance

Although catalyst shaping by extrusion has been industrially applied for decades to suppress the pressure drop, much less emphasis was put on fundamental understanding of extrusion for catalytic pastes and its effect on the properties of the final catalyst bodies. During recent years intensive research efforts have been put on synthesis of extrudates by systematically varying different synthesis parameters, methods of metal modifications, different types of binders and correlating extrudate properties with their performance in several catalytic reactions. The synthesis method of extrudates can have a large impact on properties, relevant for catalysis, including acidity/basicity, the metal location and the particle size as well as textural properties, which can differ from the properties of the corresponding powder catalysts. Furthermore, a binder can interact with the support changing physico-chemical and catalytic properties. The current review summarizes recent developments related to shaping of catalysts by extrusion addressing also such advanced methods to investigate diffusion of liquid reactants inside the extrudates and interconnectivity of pores, as pulse gradient field NMR spectroscopy and fluorescent probe analysis respectively.