pore structure, composition, and type of extraframework cations influence the
maximum uptake and adsorption kinetics of the target adsorbate. A careful analysis
of knowledge accumulated in this field thus far allows us to conclude that small-pore
zeolites will likely be further employed in the adsorption/separation of economically
useful or noxious small gas molecules. Therefore, there is still a strong need for the
synthesis of zeolites with new pore structures and/or compositions, which will in
turn lead to improved adsorbents for selective small gas capture.
Keywords Adsorption/separation · Chemical composition · Pore topology · Small
gases · Small-pore zeolites
1 Introduction
The name zeolite was first coined in 1756 when Axel F. Cronstedt, the Swedish
mineralogist, discovered that a mineral, likely stilbite (framework type STI),
desorbed water when heated [1]. Therefore, it is not surprising that zeolites and
related microporous materials are widely used in the current gas adsorption and
separation processes. However, the chemical industry still employs, for example,
energy-intensive distillation processes as a major hydrocarbon separation technology. This has considered the adsorptive separation using porous materials as an
alternative technology, due to the high energy efficiency and low material cost.
Consequently, a multitude of such solids, i.e., zeolites, metal organic frameworks
(MOFs), activated carbons (ACs), etc., have been explored as adsorbents for various
separations [2–4]. Among the solid adsorbents known to date, zeolites have a clearcut advantage over other porous materials for industrial applications, especially in
terms of physicochemical stability.
In general, zeolitic materials are hydrothermally synthesized under autogenous
pressure at 373–473 K, using synthesis mixtures containing inorganic (alkali and/or
alkaline earth cations, hydroxide or fluoride anions, and heteroatoms other than Si)
and/or organic (amines or alkylammonium ions) structure-directing agents (SDAs)
[5]. Thus, when the zeolite synthesis conditions are appropriately controlled by
varying the crystallization temperature and time; type of heteroatoms; synthesis
mixture composition; charge, shape, and size of the organic SDA; type of mineralizing agent; etc., it is possible to synthesize novel structures or compositions. The
resulting zeolites may then be applied as adsorbents for a target molecule if they
meet specific criteria like pore size and polarity, which are determined by the desired
target molecule (adsorbate).
Zeolites possess a three-dimensional (3D), four-connected framework structure
consisting of corner-sharing TO 4 tetrahedra, where T is Si or Al. While the wellknown physicochemical stability of this important class of microporous solids can be
rationalized by considering their structural and compositional features, an almost
2
K. C. Kemp et al.
maximum uptake and adsorption kinetics of the target adsorbate. A careful analysis
of knowledge accumulated in this field thus far allows us to conclude that small-pore
zeolites will likely be further employed in the adsorption/separation of economically
useful or noxious small gas molecules. Therefore, there is still a strong need for the
synthesis of zeolites with new pore structures and/or compositions, which will in
turn lead to improved adsorbents for selective small gas capture.
Keywords Adsorption/separation · Chemical composition · Pore topology · Small
gases · Small-pore zeolites
1 Introduction
The name zeolite was first coined in 1756 when Axel F. Cronstedt, the Swedish
mineralogist, discovered that a mineral, likely stilbite (framework type STI),
desorbed water when heated [1]. Therefore, it is not surprising that zeolites and
related microporous materials are widely used in the current gas adsorption and
separation processes. However, the chemical industry still employs, for example,
energy-intensive distillation processes as a major hydrocarbon separation technology. This has considered the adsorptive separation using porous materials as an
alternative technology, due to the high energy efficiency and low material cost.
Consequently, a multitude of such solids, i.e., zeolites, metal organic frameworks
(MOFs), activated carbons (ACs), etc., have been explored as adsorbents for various
separations [2–4]. Among the solid adsorbents known to date, zeolites have a clearcut advantage over other porous materials for industrial applications, especially in
terms of physicochemical stability.
In general, zeolitic materials are hydrothermally synthesized under autogenous
pressure at 373–473 K, using synthesis mixtures containing inorganic (alkali and/or
alkaline earth cations, hydroxide or fluoride anions, and heteroatoms other than Si)
and/or organic (amines or alkylammonium ions) structure-directing agents (SDAs)
[5]. Thus, when the zeolite synthesis conditions are appropriately controlled by
varying the crystallization temperature and time; type of heteroatoms; synthesis
mixture composition; charge, shape, and size of the organic SDA; type of mineralizing agent; etc., it is possible to synthesize novel structures or compositions. The
resulting zeolites may then be applied as adsorbents for a target molecule if they
meet specific criteria like pore size and polarity, which are determined by the desired
target molecule (adsorbate).
Zeolites possess a three-dimensional (3D), four-connected framework structure
consisting of corner-sharing TO 4 tetrahedra, where T is Si or Al. While the wellknown physicochemical stability of this important class of microporous solids can be
rationalized by considering their structural and compositional features, an almost
2
K. C. Kemp et al.