Zeolite catalysts heterogeneous composite

The effectiveness of zeolites in catalysis and separation can often be improved by the textural and chemical properties of the matrices in which they are imbedded. Chitosan gels issued from renewable resources are already used as supports for the preparation of heterogeneous catalysts in the form of colloids, flakes or gel beads [1, 2], In this study we present several methods for the incorporation of zeolites in chitosan matrices and characterize the synergic effect of the components on the properties of the composite. 

Zirconium dioxide and zeolites of pentasil structure are widely used as catalysts and efficient carriers in many heterogeneous reactions, and particularly in the process of selective catalytic reduction of nitrogen oxides by hydrocarbons (SCR-process) [1,2]. Synthesis of new catalytic systems for NOx SCR-process by CnHm is therefore related with searching for their optimum composition and preparation methods to attain maximum activity in this reaction. 

New types of mesoporous molecular sieves (their first synthesis opened a new subfield of molecular sieve chemistry) have been prepared over the last ten years by new synthetic approaches, different from those known for zeolites. The variety of the synthetic procedures described and the differences in the textural properties due to different synthetic procedures, as well as to the high temperature treatment, give evidence that mesoporous molecular sieves of different chemical compositions are very interesting materials not only in materials science. They could be important also for the application as heterogeneous catalysis, support for immobilization of homogeneous catalysts, adsorbents or materials for synthesis of new types of inclusion compounds. 

In particular, for the synthesis of optically pure chemicals, several immobilization techniques have been shown to give stable and active chiral heterogeneous catalysts. A step further has been carried out by Choi et al. [342] who immobilized chiral Co(III) complexes on ZSM-5/Anodisc membranes for the hydrolytic kinetic resolution of terminal epoxides. The salen catalyst, loaded into the macroporous matrix of Anodise by impregnation under vacuum, must exit near the interface of ZSM-5 film to contact with both biphasic reactants such as epoxides and water. Furthermore, the loading of chiral catalyst remains constant during reaction because it cannot diffuse into the pore channel of ZSM-5 crystals and is insoluble in water. The catalytic zeolite composite membrane obtained acts as liquid-liquid contactor, which combines the chemical reaction with the continuous extraction of products simultaneously (see Figure 11.28) the... 

An important aim of theoretical catalysis is to develop the rules that relate catalyst performance to catalyst structure and composition. In this chapter, we introduce various general rules that concern this relationship. We have already referred to steric control which can be due to the interaction between the ligands in a homogeneous catalyst, organic overlayer on a heterogeneous surface, or the cavities within zeolites. The last will be extensively discussed in Chapter 4. 

The activated carbon, owing to its porosity and chemical surface composition, both of which may be appropriately controlled, is also recommended as a suitable catalyst support [179]. On the other hand, both silica and alumina oxides as well as natural amorphous aluminosilicates and zeolites are widely used as heterogeneous catalysts. These adsorbents having acid or (and) base sites are named as solid acid-base catalysts [183]. 

Keywords catalyst preparation, heterogeneous multi porous catalyst, zeolite composite,... 

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