Silica monoliths featuring either mesopores or flow-through macropores and mesopores in their skeleton are prepared by combining spinodal phase separation and sol-gel condensation. The macroporous network is first generated by phase separation in acidic medium in the presence of polyethyleneoxides while mesoporosity is engineered in a second step in alkaline medium, possibly in the presence of alkylammonium cations as surfactants. The mesoporous monoliths, also referred as aerogels, are obtained in the presence of alkylpolyethylene oxides in acidic medium without the use of supercritical drying. The impact of the experimental conditions on pore architecture of the monoliths regarding the shape, the ordering, the size and the connectivity of the mesopores is comprehensively discussed based on a critical appraisal of the different models used for textural analysis.

Self-standing binderless FAU-X monoliths with hierarchical trimodal porosity have been synthesized for the first time by a double pseudomorphic transformation. Parent silica monoliths obtained by the combination of spinodal decomposition and sol-gel process have first been synthesized. The silica monoliths have been then transformed into silicaalumina monoliths (0.25 < Al/Si < 0.40) in low NaOH concentration ([NaOH] = 0.24 mol/L) at 40 °C for 24 h. Silica-alumina monoliths have been then transformed into FAU-X monoliths featuring nanocrystals in the struts at high NaOH concentration ([NaOH] = 2.2 mol/L) with an aging step at 40 °C for 4 days and a crystallization step at 100 °C for 24 h. The FAU-X monoliths feature macropores with diameters adjustable from 3 to 20 µm (similar to the parent silica monolith). The skeleton of the FAU-X monoliths is formed by an aggregation of two populations of FAU-X nanocrystals (100-200 nm / 400-500 nm) generating a secondary porosity between the nanocrystals of 30 to 1000 nm in diameter, centered at 300 nm. The FAU-X monoliths present three levels of porosity with a macropore volume of ca. 1.0 mL/g, a secondary pore volume of ca. 0.40 mL/g and a micropore volume of 0.30 mL/g. These new FAU-X monoliths with hierarchical porous structure fulfill the requirements of high performance adsorbents for continuous flow process intensification.