In the case of the Fe HT samples the measured pore diameters are 6.6 and 8.3 nm respectively for the two aging temperatures, Table . Following the same argument as for the case of the HT sample, this implies that the rate of the agglomerated particle growth is faster in the case of the Fe HT sample, than that for the HT sample: the crystallite sizes, based on PXRD data, do not vary significantly between the HT samples as a function of composition. Therefore, the large variation in the pore sizes could only be attributed to the differences in the sizes of the agglomerates of the crystallites.