Pore structure analysis of PFSA/SiO2 composite catalysts from nitrogen adsorption isotherms

Abstract

The perfluorosulfonic acid (PFSA)/SiO2 composite catalysts were prepared by sol-gel method. Differences concerning pore structure analysis of PFSA/SiO2 catalysts were discussed on the basis of nitrogen adsorption. Their surface area and pore size distributions were evaluated by Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods, respectively. The nitrogen adsorption-desorption isotherms associated with adsorption hysteresis of PFSA/SiO2 catalysts were analyzed in detail. The adsorption isotherms of PFSA/SiO2 catalysts belonged to Type IV isotherms accompanied by hysteresis loops of Type H1 for PFSA/SiO2 catalysts with content of 5%, 13% and 20% PFSA (PFSA-5, PFSA-13 and PFSA-20), and the hysteresis loop of Type H2 for PFSA/SiO2 catalyst with 40% PFSA content (PFSA-40). It indicated that PFSA-5, PFSA-13 and PFSA-20 catalysts had narrow pore size distributions and the well-defined cylindrical pores, while PFSA-40 catalyst had wide pore size distribution and inkbottle-like pores. The pore structure of PFSA-40 catalyst from the analysis of the hysteresis loop was not in agreement with that from BJH method. As an emendation for evaluation of pore size distributions of PFSA/SiO2 catalysts, the comparison plots method was introduced, which was helpful to evaluate the pore structure of PFSA/SiO2 catalysts more factually.