Single metal atoms and metal clusters have attracted much attention thanks to their advantageous capabilities as heterogeneous catalysts. However, the generation of stable single atoms and clusters on a solid support is still challenging. Herein, we report a new strategy for the generation of single Pt atoms and Pt clusters with exceptionally high thermal stability, formed within purely siliceous MCM-22 during the growth of a two-dimensional zeolite into three dimensions. These subnanometric Pt species are stabilized by MCM-22, even after treatment in air up to 540 °C. Furthermore, these stable Pt species confined within internal framework cavities show size-selective catalysis for the hydrogenation of alkenes. High-temperature oxidation-reduction treatments result in the growth of encapsulated Pt species to small nanoparticles in the approximate size range of 1 to 2 nm. The stability and catalytic activity of encapsulated Pt species is also reflected in the dehydrogenation of propane to propylene.

Novel layered zeolitic organic−inorganic materials (MWW-BTEB) have been synthesized by intercalation and stabilization of arylic silsesquioxane molecules between inorganic zeolitic MWW layers. The organic linkers are conformed by two condensed silyl-arylic groups from disilane molecules, such as 1,4-bis(triethoxysilyl)benzene (BTEB), which react with the external silanol groups of the zeolitic layers. The hybrids contain micropores within the inorganic layers and a well-defined mesoporous system in between the organic linkers. An amination post-treatment introduces basic groups in the organic linkers close to the acid sites present in the structural inorganic counterpart. Through this methodology it has been possible to prepare bifunctional acid−base catalysts where the acid sites are of zeolitic nature located in the inorganic building blocks and the basic sites are part of the organic structure. The resultant materials can act as bifunctional catalysts for performing a two-step cascade reaction that involves the catalytic conversion of benzaldehyde dimethylacetal into benzylidene malononitrile.

A new material of zeolitic nature, ITQ-6, has been obtained by delamination of a layered precursor of ferrierite. XRD, Ar and N2 adsorption, and 29Si and 27Al MAS NMR pyridine and 2,6-di-tert-butylpyridine adsorption show that a delaminated material with a very high external surface area has been produced. The silicoaluminate is stable upon calcination and presents strong acid sites catalytically active and highly accessible to bulky reactants. We have also obtained by direct synthesis the titanium silicate version of the laminar precursor of ferrierite and ITQ-6. The Ti is demonstrated to be in framework positions, and in the case of the TiITQ-6 is active and selective in the epoxidation of 1-hexene with H2O2. The TiITQ-6 is stable and remains active upon repeated reaction−calcination processes.

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Organic-inorganic hybrid materials with different levels of structuration and porous hierarchy and one or several types of active sites in the framework can catalyze multistep chemical processes in a one-pot reactor system following a cascade of reaction events. It will show how the different active sites can act in a synergistic or in a consecutive way following a similar functionality model to biological multisite catalysts. Research on this subject for heterogeneous catalysts is still in the beginning stage and very interesting results can be expected if we are able to successfully combine the properties of organic and inorganic catalysts.

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In the last years, covalent organic frameworks, COFs, and their derived sub-groups based on auto-assembly of exclusively aromatic units, PAFs, are emerging into the advanced materials field due to their high free porous volume, structural regularity, robustness, hydrothermal stability, and functional variety. Their high gas uptake capacities, presence of stabilized active functions in the framework and charged low-density structures combined with their organization through π-conjugated system arrays open the possibilities of COFs and PAFs to be used as effective materials for adsorption, selective separation and catalysis, and in nanotechnological applications. This review will be focused on self-assembly synthesis mechanisms, physico-chemical characteristics, and applications of this class of promising covalent porous organic structures, outlooking their possible future approaches and perspectives.