This introductory chapter intends to show to the reader the complex nature of the zeolites in a way that is simple, clear and sufficiently complete. In particular, the various compositional and structural features of zeolites are mixed together and presented step by step, to take the reader by the hand and lead him across this complex universe. In fulfilling this goal, in the first paragraph, we present the tetrahedron TO4, where T is usually Si, as the primary building unit of zeolites. Then, we explain that such tetrahedrons link to each other in the three directions of the space, giving rise to structures, which may largely differ from each other owing to the variability of the angle T-O-T. At this point, the occurrence of the isomorphous substitution in aluminosilicates is stated and particular care is taken in explaining its compositional consequences. In the second paragraph, firstly, we show the differences among the various classes of framework aluminosilicates: feldspars, feldspathoids and zeolites. In particular, their difference in chemical stability is strongly highlighted. Then, we shortly explain the nature of the hydrothermal reacting systems, which lead to the formation of zeolites as very metastable phases. Useful suggestions concerning zeolite synthesis are given. In the third paragraph, firstly, we present the Loewenstein rule, together with its consequences. Then, we present the secondary building units (SBUs) of the zeolites and explain in details how the reader has to interpret them. In particular, we explain that simple assemblies of such SBUs may allow the accurate description of all the framework topologies of zeolites. In fulfilling this goal, we describe, as an example, the structure of three zeolites (sodalite, zeolite A and faujasite largely differing from each other in the composition, structure and technological applications), strongly evidencing that their structure can be described by using the same SBUs. In the final part of this paragraph, we show how the possibility of occurrence of the isomorphous substitution in zeolites is far larger, thus giving rise to zeolite-like structures where Si and/or Al may be completely absent. In the final paragraph of this introductory chapter, we present the main, traditional, technological applications of zeolites: adsorption, cation exchange and catalysis. In particular, we explain the particular features of selectivity exhibited by the zeolites, when they are used as adsorbents, cation exchangers and catalysts. Moreover, these features are discussed in the light of their chemical composition and structure. Some examples will help the reader in evaluating the enormous abilities that zeolites exhibit in these three crucial technological fields of applications.

Introduction: A Map of the Most Intriguing Features of Zeolites

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发表日期：

2026年

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Michele Pansini,
Serena Esposito

摘要

This introductory chapter intends to show to the reader the complex nature of the zeolites in a way that is simple, clear and sufficiently complete. In particular, the various compositional and structural features of zeolites are mixed together and presented step by step, to take the reader by the hand and lead him across this complex universe. In fulfilling this goal, in the first paragraph, we present the tetrahedron TO4, where T is usually Si, as the primary building unit of zeolites. Then, we explain that such tetrahedrons link to each other in the three directions of the space, giving rise to structures, which may largely differ from each other owing to the variability of the angle T-O-T. At this point, the occurrence of the isomorphous substitution in aluminosilicates is stated and particular care is taken in explaining its compositional consequences. In the second paragraph, firstly, we show the differences among the various classes of framework aluminosilicates: feldspars, feldspathoids and zeolites. In particular, their difference in chemical stability is strongly highlighted. Then, we shortly explain the nature of the hydrothermal reacting systems, which lead to the formation of zeolites as very metastable phases. Useful suggestions concerning zeolite synthesis are given. In the third paragraph, firstly, we present the Loewenstein rule, together with its consequences. Then, we present the secondary building units (SBUs) of the zeolites and explain in details how the reader has to interpret them. In particular, we explain that simple assemblies of such SBUs may allow the accurate description of all the framework topologies of zeolites. In fulfilling this goal, we describe, as an example, the structure of three zeolites (sodalite, zeolite A and faujasite largely differing from each other in the composition, structure and technological applications), strongly evidencing that their structure can be described by using the same SBUs. In the final part of this paragraph, we show how the possibility of occurrence of the isomorphous substitution in zeolites is far larger, thus giving rise to zeolite-like structures where Si and/or Al may be completely absent. In the final paragraph of this introductory chapter, we present the main, traditional, technological applications of zeolites: adsorption, cation exchange and catalysis. In particular, we explain the particular features of selectivity exhibited by the zeolites, when they are used as adsorbents, cation exchangers and catalysts. Moreover, these features are discussed in the light of their chemical composition and structure. Some examples will help the reader in evaluating the enormous abilities that zeolites exhibit in these three crucial technological fields of applications.