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MATching zeolite SYNthesis with CATalytic activity

Periodic Reporting for period 3 - SynCatMatch (MATching zeolite SYNthesis with CATalytic activity)

Reporting period: 2018-06-01 to 2019-11-30

Zeolites are crystalline microporous materials with great interest and industrial application in the fields of molecular separations and catalysis. For successful industrial use of zeolites they should have the adequate: a) Pore dimensions (for molecular sieve and diffusion properties); b) pore topology (for reactivity); chemical composition (for active site generation and thermal and hydrothermal stability).
For the synthesis of new structures, though researchers have achieved a high degree of systematization and accumulated knowledge, there is today an important component of trial and error in the methodology. As a consequence, this research program aims to develop a new concept and methodology for the synthesis of zeolite catalysts.

By studying the mechanism of a given reaction and by developing a new methodology for the synthesis of zeolites, where the SDA used resembles to the reaction transition state species (RTS), it will possible to achieve more efficient catalysts. As a consequence, this will result in lowering the transition state energy of the reaction, boosting the catalytic activity and the efficiency of the zeolite. All these results will be traduced in lowering the energy consumption of reactants and byproducts of a given industrial process. In summary, this will result in more sustainable processes for the environment.

The overall objective of the project was to develop a new methodological and conceptual approach for the zeolite synthesis that can direct into adequate materials for pre-stablished reactions or separations. The methodology would be based on molecular recognition principles. For achieving that we have to accomplish the following objectives: a) identify the reaction transition states (RTS) species for a given reaction; b) rationalize and synthesize mimics of the RTS suitable to act as Structure Directing Agents (SDA) for zeolite synthesis; c) synthesize zeolite structures; d) introduction of active sites and zeolite crystallite size control; e) control of the reactivity and separation.
According to the objectives, we have considered two groups of catalytic process; a) A process where RTS is larger than the final product; b) A process where RTS is similar to the final product.
In parallel but connected with the above, we have worked with: a) directed zeolite synthesis by using materials that contain desired secondary building units (SBU) as the source for the synthesis of the final product; b) methods for crystal size control.
The main highlights of the results obtained are the following:
- A number of specific catalytic organic reactions within different groups, such as isomerization and transalkylation of alkyl aromatics, where selected and the RTS mimics were stablished.
- Different organic SDA mimics were designed and synthesized, and the syntheses of zeolites were carried out. One new zeolite structure (ITQ-64) and two already existing structures were obtained, which outperform product selectivity for the pre-established reactions when compared with actually used industrial catalysts (Science, 2017).
We have achieved zeolites with crystallite size in the order of 10-20 nm and zeolite monolayers by direct synthesis, materials that are of special interest when using RTS mimics with similar size than the products, and the pores opening of the zeolite obtained are smaller than the products.
With respect to active sites, we have successfully introduced BrØnsted and Lewis acid sites, together with single metal atoms, metal nanoclusters and metal nanoparticles within different zeolites (JACS 2016, Nature Materials 2017), following one-step or post-synthetic approaches. Finally, for molecular separations, a new structure has been achieved, which is able to separate ethane and ethene due to pore dimensions, pore topology and flexibility.
The achievements described, represent a progress beyond the state of the art from the point of view of: a) synthesis methodology and materials synthesized thereof; b) control of crystallite size for diffusion of products when the pore diameter can be limiting; c) introduction of well-defined active sites in a one-pot synthesis (single metal atoms) with impact in NOx removal, as well as nanoclusters and nanoparticles for various applications.