A New Method to Obtain the Pore Size Distribution for Ordered Mesoporous Materials with Cylindrical and Spherical Pores

JHONNY VILLARROEL-ROCHA; DEICY BARRERA; KARIM SAPAG

Miami (Florida)

Workshop; 6th International Workshop-Characterization of Porous Materials (CPM-6); 2012

Quantachrome Instrument - Rutgers University

Ordered mesoporous materials such as MCM-41, SBA-15 and SE3030 which exhibit cylindrical pores and, SBA-16 and KLE with spherical pores, show a strong influence on adsorption and catalytic processes due to their defined pore sizes. Textural characteristics of these materials are obtained by N2 adsorption–desorption isotherms at 77 K where the Kelvin equation is used for the calculus of the mesopores size. The Kelvin equation is considered valid for the capillary condensation theory and it is used for the evaluation of the PSD in various methods such as Barrett, Joyner and Halenda (BJH) (macroscopic method). However, it has been found that the classic methods for the PSD analysis, underestimate the average pore sizes for materials smaller than 10 nm. In this work, the PSD was evaluated from the N2 adsorption–desorption isotherms at 77 K for the different mesoporous materials previously mentioned. An improved method (VBS method) based on the BJH algorithm is proposed to be used for cylindrical as well as spherical pore geometries, by means of a modification in the Kelvin equation with the addition of a correction term (fc) and assuming appropriate mechanisms of capillary condensation and capillary evaporation. This term was obtained adjusting simulated isotherms with different values of fc to the experimental isotherm. The results were compared to those obtained by the Non-Local Density Functional Theory (NLDFT) model.