Sorption of Benzene on AlPO₄-5 Containing Various Heteroatoms and Analytical Description of the System

Abstract

Sorption of benzene on nonsubstituted AlPO4-5 occurs on adsorption centers originating from surface heterogeneity and created by structure defects. The metallic heteroatoms present in the framework of substituted AFI-type materials form additional centers able to bind the benzene molecules. This is equal to an increase of heterogeneity in comparison to nonsubstituted AlPO4-5. Sorption capacity of the MeAPO-5 materials depends on both the content of metal and its distribution throughout the crystals. The distribution parameter plays an important role and may even dominate the effect of the number of metallic heterocenters. Some of the equations based on the Polanyi−Dubinin potential theory can be accepted as suitable for characterizing the distribution of the adsorption potential and adsorption energy of the AFI-type molecular sieves. The dependence between the adsorption potential and the metal content may likely be disturbed by inhomogeneous distribution of the heteroatom centers.

Expressiveness of Adsorption Measurements for Characterization of Zeolitic Materials—A Review

“…This holds for all the isotherm equations applied and for two different adsorbates, benzene and water. Similar tendency has also been found for water adsorption on zeolite Y (Rozwadowski et al, 1993c), for benzene adsorption on aluminophosphates of AFI type (Kornatowski et al, 1999b,c;Rozwadowski et al, 1999) and ATO type , and for mesoporous MCM-41 (Rozwadowski et al, 2001). This broad spectrum of materials, exhibiting similar relations, suggests that this is a rule and implies that an analytical description of the isotherms should comprise only the pores actually involved in the process of adsorption since the measured adsorption does not depend on the total pore volume existing in the adsorbent.…”

“…At higher metal contents, adsorption potentials exceed the value of AlPO 4 -5 ( Fig. 15; Rozwadowski et al, 1999;Kornatowski et al, 1999b). The decrease in the adsorption potential value at low substitution levels may reflect strongly localized adsorption on single isolated metal centres.…”

“…tween various metal derivatives ( Fig. 7; Kornatowski et al, 1994aKornatowski et al, , 1999aKornatowski et al, ,b,c, 2001aKornatowski et al, ,b, 2003aKornatowski et al, ,b, 2004Rozwadowski et al, 1999). The isotherms show almost no increase over p/ p s ≈ 0.15 and are parallel to each other, independently of the kind of metal, its amount, etc.…”

“…Non-substituted AlPO 4 -5 reveals numerous structure defects that hinder diffusion/adsorption (Lehmann et al, 2002(Lehmann et al, , 2003aMüller et al, 1999Müller et al, , 2004Bódis et al, 2001Bódis et al, , 2002Kornatowski et al, , 1999bKornatowski et al, ,c, 2001aKornatowski et al, ,b, 2003aKornatowski et al, ,b, 2004Rozwadowski et al, 1999). Substitution of metals usually results in a more perfect structure (Kornatowski et al, 2001a(Kornatowski et al, ,b, 2003a(Kornatowski et al, ,b, 2004) and a higher sorption capacity.…”

“…8; Kornatowski et al, 2003a;Rozwadowski et al, 1999). Grinding large crystals should increase adsorption if it is limited by structure hindrances, e.g., interfaces between overgrown, inaccessible crystal regions.…”