Improved kernel of nitrogen isotherms for γ-alumina characterization

Abstract

We present a new kernel of N2 isotherms in γ-alumina, the metastable phase of α-alumina, most used in industrial applications. The dedicated kernel proposal, existing in the literature, uses cylindrical pores, as well as approximate kernels of commercial adsorption characterization equipment. TEM morphology studies of γ-alumina have shown that the material has slit-like pores rather than cylindrical pores. Thus, our kernel is based on a slit pore collection of N2 isotherms at 77 K with 10 different pores sizes, dedicated to the characterization of the micropore range. The isotherms were calculated by applying the Monte Carlo method in the grand canonical ensemble. The solid–fluid interaction parameters were validated in an α-alumina surface. The agreement between experimental and simulated isotherms, using our kernel, is superior to that obtained with cylindrical pores, confirming the experimental evidence on the nature of γ-alumina morphology. Two γ-alumina samples are investigated and we observe that 12 to 22% of the total volume consists of micropores that are not adequately characterized with approximate cylindrical kernels. We also propose an alternative approach to match the different PSDs obtained, based on hybrid kernels methodology of hierarchical adsorbents materials characterization.