Detemplating

Tunable Intracrystalline Mesoporosity by Partial Detemplation-Desilication... 

As-made zeolite Partially detemplated Calcined zeolite... 

It is evident that dedicated studies are required for each structure to optimize the template oxidation protocol. Many structures, in particular nonsiliceous, are thermally very sensitive [14, 15]. Calcination can result in a complete breakdown due to hydrolysis, redox processes, and phase transformations. The removal of templates in those systems is critical, making the development of mild detemplation techniques necessary [16]. 

We discuss here a combined process including detemplation and Fe incorporation by ion-exchange in the zeolite framework [147]. To achieve this, oxidants to decompose the organic template and Fe-cations for exchange are needed. Both requirements are in harmony with Fenton chemistry. The OH radicals can oxidize the template and the Fe-cations be exchanged simultaneously. 

It is concluded that zeoHte beta can be simultaneously detemplated and Fe-exchanged without FeO formation by treating the parent zeoHte with a Fenton reagent. The catalyst shows good performance on N2O decomposition. This one-pot process simplifies its preparation protocol and can be extended to other systems. Indeed, our approach was followed by Liu et al. [170], for preparing Fe-S BA-15 for benzylation of benzene with interesting results. 

Third Concept in Catalyst Design. Fenton Detemplation. Mild Organic Template Removal in Micro- and Mesoporous Molecular Sieves... 

By minimizing the Fe concentration (i.e., avoiding extensive Fe-exchange), zeolites, or mesoporous compounds can be detemplated at low temperatures without the need for high-temperature calcination. This third concept refers to the low-temperature Fenton detemplation. Strictly speaking, Fenton requires thermal activation but always below 100 °C. We refer here to quasi room temperature as compared to the high temperatures usually applied for calcination. 

However, even in these cases, it might be attractive to apply a mild detemplation followed by controlled heating for optimization. 

Recent reports describe more sophisticated detemplation methods. However, they are limited to mesoporous materials for the reasons described before. We show how Fenton chemistry can fulfill various missing challenges (i) it provides a powerful oxidation capacity at low(er) temperatures and (ii) it can work for microporous compounds as well. 

The approach consists of a liquid-phase oxidation using OH Fenton radicals from H2O2 for detemplation [148-150]. The radicals oxidize the organic template into CO2 and H2O while the porosity of the material is developed. The proof-of-principle of this concept is discussed for two case studies. 

I 6 Oxidation Tools in the Synthesis of Catalysts and Related Functional Materials Table 6.1 Detemplation approaches of micro- and mesoporous materials. 

Destmctive protocols II chemical detemplation under relatively mild conditions... 

Figure 6.4 Features of beta zeolite after Fenton treatment, (a) Saito-Foley adsorption pore-size distribution from Ar-physisorption for (O) parent zeolite containing the template (no porosity) ( ) Fenton-detemplated and (V) commercial NH4-form BEA.

The benefits of the method are appreciated when the textural parameters are compared. Data derived from N2-physisorption isotherms show that Fenton detemplation leads to improved textural parameters, with BET areas around 945 m g for a pore volume of 1.33 cm g , while calcination leads to reduced textural parameters (667m g 0.96cm g ). T-plot analysis, strictly speaking, is not apphcable for these bi-modal materials but it gives a good estimate. It shows that the micropore volume is doubled, which corresponds to an increase in the calculated micropore area from about... 

Controlled and selective combustion of components via thermal or chemical routes Calcination. Thermal detemplation of organic templates in micro- and mesoporous materials. Chemical detemplation protocols. Solution combustion synthesis... 

Veith, M. Gouygou, M. Detemple, A. Phosphorus Sulfur Silicon Relat. Elem. 1993, 75, 183-186. 

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