## 1 Introduction  
Zeolites are products marketed in many countries, including China, India, South Korea, United States and Japan. These nations are leaders in shipments for zeolite exportation according to the website of Volza Grow Global. Shipments from China had reached 6360 as of November 2022, followed by India (4127) and South Korea (2852). The USA had 2861 shipments, while Japan had 1165. In monetary data, according to the website Expert Market Research, the market size of zeolites reached almost USD3.8 billion in 2020 and is expected to have a compound annual growth rate (CAGR) of 5.5%, reaching almost USD5.2 billion by 2026. Zeolite's structure comprises a tridimensional framework, with atoms arranged in a tetrahedral geometric form. The general formula is TO4, where T atoms are a metal, bridged by oxygen atoms (O). The performance and properties of this material are determined by structural studies of pore volume, pore size, channel dimensionality and extra-framework species. The traditional chemical composition is similar to a typical aluminosilicate structure, where Al, Si and O are the main components. However, high or pure silica-based structures were recently synthesized. The Si atom may be changed (isomorphically substituted) by a heteroatom, likely Ge, B, Ga, Be, or P, to tune zeolite function. The charge is balanced by the presence of exchangeable extra-framework cations. There are several topologies available, varying in pore diameter, being small, medium, or large, pore systems with 1D, 2D, or 3D channels, and the presence of internal cages where compounds may react or be entrapped [1, 2]. Some metal nanoparticles can be encapsulated in these channels as shown in Figure 1, according to [2]. Since a rise of interest in the 70s, the great necessity of zeolite's use, either in industry or in laboratories, led to the creation of new structures year after year. In this scenario, different structures were produced with the same framework but different names, synthesis conditions and chemical composition. The database of zeolite structures was created by the International Zeolite Association (IZA), with 248 known topologies up to 2020. In this amount, twenty different types are natural zeolites [3]. These structures are firstly identified by their pore size and dimensionality. In terms of pore size classification, the channel classification is determined by the number of T atoms delimiting the smallest pore opening, being small (8 T atoms ring), medium (10 T atoms ring) and large (12 T atoms ring) [1]. The zeolites may be classified according to their pore size, where those with diameter less than 2 nm are microporous. If the diameter is between 2 and 50 nm, the structure is mesoporous, and up to 50 nm it is classified as macroporous. The presence of mesopores could be beneficial to the catalyst lifetime (reducing the coke formation) and for the mass transmission [4]. The pore size of the structure determines how fast and efficient the physicochemical process is. Obviously, bulky molecules can enter the porous  
Figure 1: Metal nanoparticles encapsulated in MFI structure. Reproduced from [2]. Copyright ACS 2019.  
structure only if the molecular size is smaller than the pore size. Increasing the molecular size or reducing the pore size would slow the diffusion rate until its total inefficiency. The molecular diffusion rate within the zeolite might be less than the Knudsen diffusion. Kim et al. [5] showed how pore size is important in characterization of mesoporous materials from silicate waste. There are many applications of mesoporous ordered zeolites, for instance, for the adsorption of As (V) [6], the cracking of oil to produce liquid hydrocarbon fuel [7], for the valorization of agro-industrial waste [8], and the immobilization of enzymes for biocatalytic processes. For this purpose and an environmentally friendly production process, zeolite synthesis can be performed using wastes from different industrial sectors.