Over the last decades, synthesis of ordered mesoporous materials has been widely studied because of their unique textural properties. In heterogeneous catalysis, their atypical pore networks (2D to 3D long range ordered mesopore networks) provide easy mass transfer of reactants and products to active sites. However, for some specific industrial catalytic processes, internal diffusion limitations always occur, especially for reactions involving large biopolymers and/or triglycerides. The stabilisation of a multiscale porosity in the material can allow the elimination of such constraints during reaction and can have a positive impact on the catalyst activity.
In this study, hierarchical monoliths with multiscale porosity (micro/meso/macro) have been produced from a mesoporous silica powder (SBA-15, 750-800 m²/g) by using a « ceramic » approach. Strategy of preparation involves the replication of sacrificial polymer beads dispersed in an optimised slurry of mesoporous silica. After thermal treatment, the results indicate that monolithic meso-/macroporous materials showing an interesting mechanical stability can be prepared (compressive strength up to 86 kPa for 276 m²/g of specific surface area). This approach is also interesting since it allows the easy incorporation of binders such as bentonite or glass frits. In particular, adding 2 wt.% of bentonite to SBA-15 slurries greatly improves the mechanical stability of the final objects, after heat treatment at 900°C, while retaining similar specific surface area (up to 343 kPa for 305 m²/g).
Obtained monoliths have a multiscale porosity: a secondary micro- and a main mesoporosity from the amorphous SBA-15; a micrometer-sized interparticular “small” macroporosity between the silica grains in the walls of the monoliths; and a “large” macroporosity produced by the replication of the polymer beads.