Assembly of a hierarchical zeolite-silica composite by spray drying

We report a one-step spray drying synthesis of a multimodal composite based on a polymer-templated silica matrix enclosing a mesoporous ZSM-5 zeolite. The first level of porosity, comprising the silica matrix with 13-25 nm mesopores, is generated by evaporation-induced assembly of the silica nanoparticles together with the non-ionic surfactant using spray drying. The mesoporous zeolite contributes with micropores (0.56 mm) and intracrystalline mesopores (similar to 7 nm) introduced by controlled alkaline leaching. The nanostructured composite, featuring agglomerated zeolite microgranules uniformly covered by the silica, displayed tuneable properties of the matrix mesoporosity and particle size by changing both the silica source and the spray drying conditions. The structural and acidic properties of the zeolite phase were not altered by the assembly method. The technique was successfully applied to other zeolite structures (USY, mordenite and ferrierite) with no impact in the characteristics of the matrix. This fast, versatile, reproducible, economical and scalable technique represents a powerful strategy for creating hierarchically structured materials with adjustable micro-, meso- and macroporous properties and enhanced agglomeration.