Surface area per volumetric loading and its practical significance

Abstract

The surface area of porous materials is a widely-used parameter in catalysis and adsorption. The most-commonly applied model, Brunauer–Emmett–Teller (BET), bases the parameter to the mass of material. Though the model does have its limitations, comparisons among materials are widely done to rank them from low to high surface areas, and to make correlations with other properties. However, in practical terms volume is often more appropriate since the design of reactors and adsorption columns aims at minimizing their volume. Thus, in such cases the surface areas can be better expressed per material bed volume using the bulk density. In this communication, we discuss the concept of volumetric surface area as m2/cm3MatBed, showing remarkable new insights. We applied this concept to two mesoporous silica-based materials with comparable pore size and C values. A material which was far superior in terms of conventional surface area (561 versus 227 m2/gMat), they both became comparable in terms of m2/cm3MatBed (ca. 110 both) due to the much lower density of the former material. In other words, being superior in gravimetric terms does not guarantee to be volumetrically superior. The results highlight the importance of considering the material bulk density when comparing surface areas of porous materials for applications where volume is critical.