## 4 Applications of Zeolites in Catalysis, Bioprocesses, and Environmental Remediation
### Enzyme Immobilization
Once formed, the immobilized peroxidase can catalyze many important chemical processes, such as the hydroxylation of aromatic compounds in biotransformations [343], the soil detoxification and bioremediation of water bodies containing phenols, cresols and chlorinated phenols [344], with possible use in different reactions routes as showed for peroxygenase by Pellegrini et al. [345], in biotechnological processes such as in the development of diagnostic kits for the quantification of uric acid, glucose, cholesterol and lactose [346]. In the bioremediation of water bodies, the supported enzyme has potential use in the degradation of dyes acting in the degradation of anthraquinone dye. The removal of aromatic compounds in effluents has involved HRP and LiP enzymes, which once immobilized can be easily used in the treatment of contaminants such as anilines, hydroxyquinolines, benzidines and naphthylamines. The mineralization of recalcitrant aromatic compounds and oxidation of polycyclic aromatic compounds are other possibilities. With regard to the soil detoxification process, the immobilized enzymes can be useful in the biotransformation of atrazine herbicides such as diethylatriazine and hydroxyatriazine [344]. Figure 19: Schematic diagram of enzyme immobilization on zeolite through chemical methods. (**a**) Using glutaraldehyde for covalent anchoring; (**b**) entrapment of enzyme aggregates in mesoporous structure. Reproduced from [340]. Copyright 2021 Elsevier. In the degradation of mycotoxins, peroxididases show activity against aflat B1 and M1, deoxynivalenol, ochratoxin A and zearalenone. In the food industry, they stand out as indicators of the efficiency of thermal processing of fruits and vegetables due to their relatively high thermal stability, a feature that have better behavior when the enzyme is stabilized in a support [346]. Application in biotechnological processes demands knowledge of zeolite's properties, such as the low water solubility of substrates of interest, which has been remedied using hydrophobic matrices acting as a reservoir for substrates and products. The high temperature is a limiting factor for its activity. Such characteristics are considered in the elaboration of diagnostic kits in which peroxidase is very useful for generating chromogenic products at relatively low concentrations and good stability [346] (p. 40). The physical or chemical attachment of protein in FAU zeolites can maintain the low solubility because of the Si content presented in some types of zeolites with this structure such as NaY. The thermal stability offered by zeolite structure can avoid the temperature effects in enzyme optimizing its use. The FAU zeolites are structures that deserve more attention to increase the lifetime and the activity of peroxidase enzymes through immobilization. Other research fields might develop besides the actual ones used where the product (zeolite) is just synthesized and chemically modified as in insertion of a strong acid behavior as in the use of some transition metal for incorporation of its structure. These most used applications have a limited field of study, exploring just the material properties for physicochemical processes. This structure is known to be obtained by natural precursors, e.g., wastes, increasing the value as an eco-friendly material and the incorporation of a biocatalyst, that can be obtained from natural sources as well, represents a sum of two possibilities for production a new material with wide range of applications and with less cost in comparison to the synthetic routes using organic solvents and other chemicals that offer great risk for the production process.