are carried out up to atmospheric pressure, although in some cases when CO 2 is used,
it is necessary to reach higher pressures.
In this chapter, we introduced an overview of the textural analysis by
physisorption applied to zeolites, including a few suggestions to obtain in-depth
and reliable information about the studied samples.
The previous knowledge about the material to be studied is crucial to select the
most suitable experimental conditions, such as sample pretreatment, adsorptive,
pressure range, and analysis temperature to obtain the adsorption isotherm. It is
worth to emphasize that a complete and reliable isotherm must be measured since
from it; all the textural properties will be obtained.
The adsorptive selection is related to both the characteristics of the zeolite and the
required information. Nitrogen at 77 K is the most used adsorptive to obtain the
specific surface area and to evaluate the mesoporosity. In the presence of functional
surface groups, Ar at 87 K is the suggested adsorptive due to the lack of quadrupole
moment. However, Ar at 77 K can also be used only to obtain information about the
micropore region. For samples with narrow micropores, CO 2 at 273 K is the
alternative adsorptive due to its mobility to access in these pores.
The BET method is still widely used for determining the specific surface area of
micro–mesoporous materials. However, it should be clearly stated that, in the
presence of micropores, as in zeolites, the application of this method only leads to
an apparent surface area (i.e., S BET ), which serves as a useful “fingerprint” of the
adsorbent.
To analyze the micropore volume is advisable to use the plots methods; in
particular, α S -plot is the most reliable method (if we have the corresponding standard
isotherms). Furthermore, additional information such as external surfaces (S ext ) of
the samples can be obtained, from which the contribution of the micropores to S BET
can be calculated.
To obtain the PSD of zeolites is advisable to evaluate the microporous and
mesoporous region separately, considering that there is not a unique and suitable
method that allows assessing the complete range of pores. To obtain a micropore size
distribution, the HK methods and its modifications as SF and CY, work well, and
their results agree with theoretical value for the zeolite structure. Regarding the
mesoporous region, VBS and DFT methods give the best information.
In summary, it is recommended to carry out good experiments, based on the
previous knowledge of the samples, and take into account the adequate models or
methods, to analyze the different textural properties of zeolites.
References
1. Moshoeshoe M, Nadiye-Tabbiruka MS, Obuseng V (2017) A review of the chemistry, structure, properties and applications of zeolites. Am J Mat Sci 7(5):196–221
2. Baerlocher C, McCusker LB, Olson DH (2007) Atlas of zeolite framework types, 6th edn.
Elsevier, Amsterdam
52
J. Villarroel-Rocha et al.
it is necessary to reach higher pressures.
In this chapter, we introduced an overview of the textural analysis by
physisorption applied to zeolites, including a few suggestions to obtain in-depth
and reliable information about the studied samples.
The previous knowledge about the material to be studied is crucial to select the
most suitable experimental conditions, such as sample pretreatment, adsorptive,
pressure range, and analysis temperature to obtain the adsorption isotherm. It is
worth to emphasize that a complete and reliable isotherm must be measured since
from it; all the textural properties will be obtained.
The adsorptive selection is related to both the characteristics of the zeolite and the
required information. Nitrogen at 77 K is the most used adsorptive to obtain the
specific surface area and to evaluate the mesoporosity. In the presence of functional
surface groups, Ar at 87 K is the suggested adsorptive due to the lack of quadrupole
moment. However, Ar at 77 K can also be used only to obtain information about the
micropore region. For samples with narrow micropores, CO 2 at 273 K is the
alternative adsorptive due to its mobility to access in these pores.
The BET method is still widely used for determining the specific surface area of
micro–mesoporous materials. However, it should be clearly stated that, in the
presence of micropores, as in zeolites, the application of this method only leads to
an apparent surface area (i.e., S BET ), which serves as a useful “fingerprint” of the
adsorbent.
To analyze the micropore volume is advisable to use the plots methods; in
particular, α S -plot is the most reliable method (if we have the corresponding standard
isotherms). Furthermore, additional information such as external surfaces (S ext ) of
the samples can be obtained, from which the contribution of the micropores to S BET
can be calculated.
To obtain the PSD of zeolites is advisable to evaluate the microporous and
mesoporous region separately, considering that there is not a unique and suitable
method that allows assessing the complete range of pores. To obtain a micropore size
distribution, the HK methods and its modifications as SF and CY, work well, and
their results agree with theoretical value for the zeolite structure. Regarding the
mesoporous region, VBS and DFT methods give the best information.
In summary, it is recommended to carry out good experiments, based on the
previous knowledge of the samples, and take into account the adequate models or
methods, to analyze the different textural properties of zeolites.
References
1. Moshoeshoe M, Nadiye-Tabbiruka MS, Obuseng V (2017) A review of the chemistry, structure, properties and applications of zeolites. Am J Mat Sci 7(5):196–221
2. Baerlocher C, McCusker LB, Olson DH (2007) Atlas of zeolite framework types, 6th edn.
Elsevier, Amsterdam
52
J. Villarroel-Rocha et al.