Permeability of silica monoliths containing micro- and nano-pores

Abstract

For applications as catalyst supports in flow reactors, porous silica monoliths require a combination of connected pores of micron-scale to enable fluid flow plus nm-scale pores to enable high catalyst area and activity. We have synthesised a range porous silica monoliths, characterised their micron and nm-scale pores and measured their permeability coefficients K. K can be controlled over the range 10−10–10−14 m2, primarily by adjustment of the polymer/silane concentration ratio, whilst maintaining the specific surface area and nm-scale porosity approximately constant. For the majority of the silica monolith samples, the measured permeability coefficient K is 2–5 times smaller than K for a hypothetical reference system consisting of a monolith with uniform cylindrical pores aligned in the flow direction and with the same average pore diameter and volume fraction.