Maksym Opanasenko

Metal organic frameworks as heterogeneous catalysts for the production of fine chemicals

This review focuses on the use of metal organic frameworks (MOFs) as catalysts for the synthesis of fine chemicals. While petrochemistry is characterized by gas phase reactions, in which MOFs cannot compete with robust zeolites, MOFs are better suited for liquid phase reactions performed at moderate temperatures. These are the conditions typically employed for the production of fine chemicals characterized by being more complex and diverse molecules of low volatility, but with high added value. For the preparation of this type of compound, MOFs offer the advantage of wide open porosity in the nanometer scale and a large void volume. In the present review we have summarized the reports that appeared up to early 2013 on the use of MOFs as catalysts in the liquid phase for the production of fine chemicals, primarily classified according to the type of active site and the functional group formed in the reaction. Prospects for future development in this field are provided in the last section.

Comparison of the catalytic activity of MOFs and zeolites in Knoevenagel condensation

The catalytic behavior of metal–organic-frameworks (MOFs) CuBTC and FeBTC was investigated in Knoevenagel condensation of cyclohexane carbaldehyde and benzaldehyde with active methylene compounds and compared with zeolites BEA and TS-1. High yields were achieved over the CuBTC catalyst in the Knoevenagel condensation involving malonitrile, especially at a relatively low reaction temperature (80 °C); no leaching of the active phase was evidenced. In contrast, zeolites were not active under such reaction conditions. We propose an activation of malonitrile on a pair of adjacent Cu ions to explain the high catalytic activity of CuBTC with respect to conventional catalysts. Compared with CuBTC, zeolites exhibited usually lower selectivities, which is ascribed to a high acid strength of their active sites promoting consecutive reactions.

Heterogeneous Pd catalysts supported on silica matrices

Palladium catalysts deposited over different types of silica (amorphous silica, mesoporous molecular sieves, solids obtained by co-condensation of silicate precursors and many others) modified with suitable donor moieties have gained enormous importance due to their wide application as catalysts for cross-coupling and other synthetically useful organic reactions. This work provides an overview of the chemistry of silica-supported palladium catalysts in different types of organic transformations in order to present the major features, advantages and limitations of various supports and immobilised ligands.

Two-dimensional zeolites in catalysis: current status and perspectives

Two-dimensional zeolites have been studied and developed as diverse and fundamentally new forms of 3D framework structures. They can produce structures such as pillared, delaminated, interlamellar expanded and others, offering improved access to active sites and enhanced diffusion of reactants and products. This has been useful in catalysis showing particular benefits for reactions of larger reactants. Primary layered zeolite forms have been obtained by direct synthesis and also by degradation of existing frameworks with built-in weaknesses. Additional forms are obtained by post-synthesis modifications. This contribution presents an overview of results from catalytic testing of various 2D zeolites especially in comparison to their conventional 3D counterparts.

Solid Acid Catalysts for Coumarin Synthesis by the Pechmann Reaction: MOFs versus Zeolites

The catalytic behavior of metal–organic frameworks Cu‐benzene‐1,3,5‐tricarboxylate (CuBTC) and Fe‐benzene‐1,3,5‐tricarboxylate (FeBTC) was investigated in the Pechmann condensation of different phenols (resorcinol, pyrogallol, and naphthol) with ethyl acetoacetate and compared with large‐pore zeolites beta (BEA) and ultrastable Y (USY). Zeolites BEA and USY exhibited high activity in transformations of the most active substrates (resorcinol and pyrogallol) but a low conversion of naphthol was observed. Almost total transformation of naphthol (94–98 % conversion) to the target product was achieved within 24 h of the reaction time over CuBTC and FeBTC. We assume that the regularity in the arrangement of active sites within the framework of CuBTC, which results in the existence of 2 active centers in close proximity, is of critical importance to the transformation of naphthol in the Pechmann reaction that leads to coumarin.

Hierarchical hybrid organic-inorganic materials with tunable textural properties obtained using zeolitic-layered precursor.

Novel layered zeolitic organic-inorganic materials have been synthesized using a two-dimensional zeolite precursor IPC-1P prepared by a top-down approach from zeolite UTL. The formation of porous materials containing organic linkers or polyhedral oligomeric siloxane covalently bonded to zeolite layers in the interlayer space was confirmed by a variety of characterization techniques (N2/Ar sorption analysis, XRD, (29)Si and (13)C NMR, TEM). The organic-inorganic porous hybrids obtained by intercalation with silsesquioxane posessed layered morphology and contained large crystalline domains. The hybrids exhibited mesoporous or hierarchical micro-/mesoporous systems, stable up to 350 °C. Textural properties of the formed zeolitic organic-inorganic materials can be controlled by varying the linker or synthetic conditions over a broad range. Surface areas and pore volumes of synthesized hybrids significantly exceed those for parent zeolite UTL and corresponding swollen material; the amount of micropores increased with increasing rigidity and size of the organic linker in the order biphenyl > phenylene > ethanediyl.

Zeolites with Continuously Tuneable Porosity

Zeolites are important materials whose utility in industry depends on the nature of their porous structure. Control over microporosity is therefore a vitally important target. Unfortunately, traditional methods for controlling porosity, in particular the use of organic structure-directing agents, are relatively coarse and provide almost no opportunity to tune the porosity as required. Here we show how zeolites with a continuously tuneable surface area and micropore volume over a wide range can be prepared. This means that a particular surface area or micropore volume can be precisely tuned. The range of porosity we can target covers the whole range of useful zeolite porosity: from small pores consisting of 8-rings all the way to extra-large pores consisting of 14-rings.

Deactivation Pathways of the Catalytic Activity of Metal–Organic Frameworks in Condensation Reactions

In the present study we have selected three different condensation reactions as model reactions, namely the hydroxylalkylation of anisole by paraformaldehyde to bis(methoxyphenyl)methane, the Pechmann condensation of phenols with ethyl acetoacetate (EAA) to coumarins and the Knoevenagel condensation of two aldehydes with three active methylene compounds to form α,β‐unsaturated esters and nitriles, using two related Fe‐containing metal–organic frameworks (MOFs), namely commercial Fe(BTC) (BTC: 1,3,5‐benzenetricarboxylate) and synthetic MIL‐100(Fe) as the catalysts. The main aim of this study was to determine the nature of the poisons, the MOF structural stability in connection with the substrate, and the variations in the product selectivity. We have found that undesired intermediates (bisarylmethyl cation in the case of hydroxyalkylation) or byproducts (benzoic acid in the case of Knoevenagel condensation) can poison the MOF by being strongly adsorbed within the MOFs and blocking the pores. In the Pechmann condensation, besides pore blocking, a low structural stability of Fe(BTC) was reflected in the collapse of the crystal structure, while using polyhydroxy aromatic compounds because of their ability to act as ligands for Fe3+, replacing trimesate ligand. MIL‐100(Fe) was considerably more robust for this reaction.

Synthesis of isomorphously substituted extra-large pore UTL zeolites

The influence of various synthesis parameters (e.g. gel composition, pH of the reaction mixture, duration of crystallization) on the phase selectivity of zeolite formation in germanosilicate reaction medium in the presence of different three-valent heteroatoms (B, Al, Ga, Fe or In) was systematically studied and compared with a controlled crystallization from pure germanosilicate media. The boundary conditions of the formation of the pure phase of isomorphously substituted extra-large pore zeolite UTL were established. In the presence of 1 mol% of the respective heteroelement in the initial gel the pH borders of UTL formation are found to be 7.5–11.9 for Fe-, 7.8–12.0 for B-, 8.2–11.0 for Ga-, 11.0–12.0 for In-, and 11.3–12.0 for Al-containing reaction mixtures. The maximum concentration of heteroelements in the reaction mixture for the successful synthesis of UTL is 1.5 mol% for Al and Ga, 6 mol% for In, and 13 mol% for B. The size of UTL crystals decreases in the order Al- > In- > Ga- > Fe- ≈ B-UTL. The nature of isomorphous substituent influences the textural properties (pore size distribution) of the respective UTL zeolites.

Superior Performance of Metal–Organic Frameworks over Zeolites as Solid Acid Catalysts in the Prins Reaction: Green Synthesis of Nopol

The catalytic performance of a set of metal-organic frameworks [CuBTC, FeBTC, MIL-100(Fe), MIL-100(Cr), ZIF-8, MIL-53(Al)] was investigated in the Prins condensation of β-pinene with formaldehyde and compared with the catalytic behavior of conventional aluminosilicate zeolites BEA and FAU and titanosilicate zeolite MFI (TS-1). The activity of the investigated metal-organic frameworks (MOFs) increased with the increasing concentration of accessible Lewis acid sites in the order ZIF-8<MIL-53(Al)<FeBTC<MIL-100(Cr)<MIL-100(Fe). Unwanted β-pinene-like isomerization takes place on the strong Brønsted acid sites of zeolites BEA and FAU, which showed significantly lower selectivity to the target nopol than the MOFs. Its high activity, the preservation of its structure and active sites, and the possibility to use it in at least three catalytic cycles without loss of activity make MIL-100 (Fe) the best performing catalyst of the series for the Prins condensation of β-pinene and paraformaldehyde. Our report exemplifies the advantages of MOFs over zeolites as solid catalysts in liquid-phase reactions for the production of fine chemicals.