Comparison of Nitrogen Adsorption and Mercury Penetration Results. Pore Size Distributions for a Series of Mo-A1 2 O 3 Catalysis with Increasing MoO 3 Content

Scanning electron microscopic data, X-ray diffraction patterns and porosity measurements are consistent with a structure for an Mo-A1₂O₃ catalyst series containing a single surface layer of Mo up to the point where the Mo loadings exceed the amount required for a monolayer. For greater Mo loadings than required for a monolayer, three dimensional orthorhombic MoO₃ is also present. The cumulative pore volume, on an alumina basis, does not appear to be significantly altered by MoO₃ loadings up to about 15 wt.%. The BET surface area, on an alumina basis, remains constant with Mo loading. However, the apparent surface area calculated from mercury penetration data decreases with Mo loading. For these materials with cylindrical pores, the Broekhoff-deBoer model for the calculation of pore size distributions produced closer agreement to the mercury penetration pore size distribution. This is in contrast to materials composed of nonporous spheres where the Broekhoff-deBoer model provided poorer agreement to mercury penetration results than either the Cohan or a packed sphere model. The results show that, within a factor of two the pore size distributions calculated from nitrogen adsorption and mercury penetration data are comparable.