Monolithic Al₂O₃ Xerogels with Hierarchical Meso‐/Macropore System as Catalyst Supports for Methanation of CO₂

Abstract

Cylindrical, cm-sized monolithic Al 2 O 3 xerogels with hierarchical meso-/macropore system were prepared by sol-gel synthesis. The influence of both solvent exchange and drying on monolith stability and the resulting pore system was studied following mass and volume of the monolith as well as by porosimetry and electron microscopy. Crack-free drying of the monoliths requires a proper management of drying stress. This is achieved by adjusting the drying rate and solvent exchange procedure applied to the intermediate lyogels. Moreover, mainly through differences in capillary pressure, changing the pore fluid allows an adjustment of the mesopore width from 7.6 nm to 10.5 nm. Neither solvent exchange nor drying affect the macropores, the width of which stays at 1.5 μm. Finally, CO 2 methanation over Ni-impregnated Al 2 O 3 monoliths reveals CO 2 conversion and CH 4 selectivity comparable to an industrial Ni/Al 2 O 3 benchmark catalyst.