Determination of the cause of mercury entrapment during porosimetry experiments on sol-gel silica catalyst supports

In previous work, a modeling methodol. was developed to det. statistical information, similar to that which can be obtained from 1H MRI, on the spatial distribution of different pore sizes within porous media using mercury porosimetry. The new methodol. has the advantage over MRI that it is suitable for application to chem. heterogeneous materials of interest in catalysis, such as coked catalysts and supported metals, that are not amenable to quant. studies using conventional 1H MRI. However, the new methodol. relied upon the theory that the entrapment of mercury within many porous solids, such as sol-gel silicas, occurs because the spatial distribution of pore sizes within the material is not random, but is, in fact, highly correlated. Mercury entrapment is thought to occur in isolated, macroscopic (>10 micro m in size) domains, contg. similarly sized larger pores, that are completely surrounded by continuous networks of smaller pores. In this work mercury porosimetry expts. on silicas, consisting of a primary intrusion and retraction cycle, followed by re-injection of mercury and secondary retraction, have shown that the entrapment of mercury does not arise due to the alternative possibility of irreversible pore structural collapse. Light microscopy studies of transparent samples following mercury porosimetry expts. have confirmed that the spatial distribution of entrapped mercury is highly heterogeneous and occurs in particular macroscopic regions within the sample. These findings support the underlying theory of mercury entrapment used in previous simulations of the mercury porosimetry expt. [on SciFinder (R)]