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Bulky epoxides are industrially produced by organic synthesis in multistep procedures, generating significant amounts of waste products in the process. Efficient catalyst in combination with a simple oxidant (H2O2 or O2) would significantly reduce the waste production. Four types of microporous titanosilicates with extra-large pores (Ti-UTL), and shortened diffusion pathways (L-TS, Ti-MCM-22, and Ti-SPP) were prepared and investigated in the epoxidation of cyclooctene with H2O2 and photocatalytic oxidation using O2. Ti-UTL is a zeolite possessing 14−12-ring channel system. l -TS-1 and Ti-MCM-22 are composed of aggregates of titanosilicate nanosheets with the thickness of ca. 2 nm and hexagonal thin platelets, respectively. Ti-SPP is composed of olive-like aggregates with approximately length of 0.88–1.12 μm and width of 0.44−0.68 μm consisting of intergrown (self-pillared) nanosheets having 13−70 nm in size. In the epoxidation with H2O2 as an oxidant, Ti-MCM-22 showed the highest catalytic activity due to the wide interlayer space, which enhanced the accessibility of cyclooctene to active titanium site. While, in the photocatalytic epoxidation in the presence of O2 instead of H2O2, Ti-UTL showed the highest activity. The incorporated germanium atoms, which is indispensable component for the construction of extra-large pores, may affect the electronic properties of active titanium species, leading to high photocatalytic activity.

Transitioning towards green chemistry requires designing sustainable processes to produce both inexpensive and environmentally friendly materials capable of catalyzing complex chemical transformations in fine chemistry. In this context, natural silicate-based catalysts stand out as some of the most promising alternatives, yet vermiculites have been mostly overlooked so far, despite their high potential as clay catalysts with high negative layer charge, high number of exchangeable interlayer cations and high Lewis and Bronsted acidity. Thus, this work reports a previously undescribed and unusual reaction between benzaldehyde and dioxane in the presence of natural and ion-enriched (Al3+, Fe3+, Mg2+, Ni2+, Sn4+) vermiculite catalysts. The effects of different vermiculites on the reaction were assessed both at different activation/calcination temperatures (150 °C, 300 °C and 450 °C) and without activation. Regardless of temperature activation, all vermiculites catalyzed C-C bond cleavage, decarbonylation/ decarboxylation and radical oxidative coupling of benzaldehyde and dioxane, albeit in different yields. Non-activated, natural vermiculite provided the highest benzaldehyde conversion (92 %) and benzaldehyde-based selectivity to the coupling product, 1,4-dioxan-2-yl benzoate (11 %). High benzaldehyde conversion rates were observed also in reactions with aluminum-enriched vermiculite (Al-VMT) activated at 150 °C (84 %), providing 10% selectivity to the coupling product, and with iron (III)-enriched vermiculite (Fe-VMT) (38 % benzaldehyde conversion, 12% selectivity). Catalyst calcination prevented the formation of the 1,4-dioxan-2-yl benzoate while simultaneously enhancing benzaldehyde degradation to benzene. Ultimately, this study shows, for the first time, that vermiculites catalyze radical-oxidative coupling, yielding complex structures such as 1,4-dioxan-2-yl benzoate, which can be used as building blocks in fine chemistry.

Porous materials are outstanding catalysts in various reactions using confinement and shape selectivity effects. Unsurprisingly, extensive research has been conducted on zeolites, pillared clays, metal oxides, metal organic frameworks, and mesoporous materials. In particular, selective oxidation of hydrocarbons stands out an important class of reactions, but the ability to avoid over-oxidation remains a challenge. Thus, the present review highlights the latest findings on octahedral and tetrahedral catalytic materials in oxidation reactions, primarily focusing on types of reactive oxygen species and approaches to their investigation, on the incorporation of different heteroatoms (Ti, Sn) into silica matrices for catalytic purposes and corresponding types of reactions and on surface engineering and design of “single-site catalysts”. In addition, composite catalysts for one-pot selective oxidation reactions are reviewed, providing examples from photochemistry including “single-site photocatalysis”, electrocatalysis, and integration of metal complexes with functional solid materials. Ultimately, the end goal of this review is to discuss current state-of-the-art approaches that are being used in the area of selective catalytic oxidations with some novel porous materials. This includes methods that are being used to study mechanistic details as well as new catalysts and new substrates for such oxidations.

International audience; Magnetic Fe@Y composites (carbon coated magnetic iron nanoparticles incorporated in Y zeolite) with 5-8 wt% Fe were synthesized and characterized. Overall acidity of the samples ranges between 2.0 and 2.47 mmol/g and is given mostly by Lewis acid sites. The obtained materials were proven to catalyze the hydrolysis of Ulvan polysaccharide with high conversions. The distribution of the reaction products depends on the reaction conditions and the concentration of Ulvan. The catalytic properties-catalytic performances correlations clearly show the acid zeolite Y is the active phase for Ulvan hydrolysis while the iron nanoparticles enable the catalyst separation in a magnetic field. Under oxygen pressure, the selectivity was completely changed to succinic acid. All Fe@Y composites were recycled for 10 times with no change in the catalytic performances after a simple magnetic separation and washing with water.

The zeolite activity in processes driven by Bronsted acid sites is determined by the distribution of the protons in the zeolite and strength of their interaction with the framework. This study aims to assess how much the transformation from three-dimensional (3D) bulk zeolite to its corresponding two-dimensional (2D) layered form changes the proton distribution and strength of the proton-framework interaction and thus how much it affects the zeolite Bronsted acid strength. Zeolites with three distinct topologies, MWW, PCR, and MFI, which form also layered analogues with considerably different thickness and silanol density were considered. To probe the Bronsted acidity of both 3D and 2D forms, an array of typical acidity descriptors (i.e., O-H stretching frequency, shift of O-H frequencies upon adsorption of CO probe molecule, C-O stretching frequencies and adsorption enthalpies of the CO adsorption complex) have been evaluated, employing both dispersion-corrected density functional theory and Fourier-transform infrared spectroscopy. Using these descriptors, the Bronsted acidity of 2D form is, on average, the same or just slightly lower than that of the 3D form. Transformation to layered form does affect the proton distribution and values of acidity descriptors for individual T sites, however, if all T sites are considered, the aggregate effect is almost negligible. Hence, these results suggest that a larger effect of the 3D -> 2D transformation can be expected for frameworks with fewer distinct T sites.

International audience; The NH4F etching is a chemical approach for the preparation of hierarchical zeolites without substantial modification of their framework composition and acidic properties. We employed this approach to modify the 2-dimensional form of ZSM-5 and obtain a catalyst for bulky molecules conversion. The etching conditions were varied in order to obtain hierarchical ZSM-5 with different level of dissolution. Thus, obtained derivatives of 2-dimensional ZSM-5 were thoroughly studied in order to get deep insights into the effect of fluoride treatment. The 2-dimensional ZSM-5 was found unexpectedly stable under etching conditions, which is a consequence of the high quality of zeolite crystals containing a limited number of defect zones and misoriented crystalline domains, in contrast to conventional ZSM-5. Fluoride etching was also used to de-pillar 2-dimensional ZSM-5. The morphology and textural properties of the de-pillared ZSM-5 were very similar to those of the parent layered ZSM-5. Accordingly, amorphous and extra-framework species were dissolved first, resulting in the complete removal of extra-framework Al, thereby strengthening the active sites. In summary, the fluoride etching opens the structure of layered ZSM-5 and strengthens its acid sites when combined with dealumination during calcination.

Titanium-containing zeolite-based catalysts have been synthesized and investigated as catalysts in methyl(phenyl)sulfide oxidation with hydrogen peroxide. A hierarchical TS-1 prepared by the secondary templating and a layered TS-1 without and with silica and silica-titania pillars have been studied. Conventional TS-1 was a benchmarking material. The study focuses on observation of the different catalytic performance with regard to textural properties; presence and volume of mesopores and different diffusion characteristics. Thus, a deficiency and excess of the oxidizing agent were used in the catalysed reactions and the progress of reaction and selectivity to products were studied. All tested catalysts have shown after 240 min almost total conversion of methyl(phenyl)sulfide with different selectivity (substrate/catalyst mass ratio 10). It was observed that the reactants ratio hydrogen peroxide/ methyl(phenyl)sulfide influences the selectivity to sulfoxide or sulfone over a particular catalyst. In the case of hydrogen peroxide deficiency experiments (H2O2/sulfide = 0.5 mol/mol) the catalysts exhibited different distributions of products. Lamellar catalyst provided 100% selectivity to sulfoxide, the others in range of 90–65% selectivity to sulfoxide; however, the selectivity was independent on the reaction time and substrate conversion. In the case of the excess of the oxidant, except for Ti-pillared TS-1, all the catalysts showed stabile selectivity of 65% towards methyl(phenyl)sulfoxide being independent of the catalyst. The Ti-pillared TS-1 has shown, during the reaction progress, a decrease in the selectivity to sulfoxide from initial 60% to final 20% of sulfoxide at almost total conversion. The only case when higher selectivity to sulfone was achieved was gradual dosing of hydrogen peroxide.

Citronellol is one of the most widely used fragrances for bouquetting purposes and it is a starting material for synthesis of several other terpenoids. Nevertheless, few data have been reported on citronellol selective oxidation. Accordingly, we report our findings on the selective oxidation of citronellol with hydrogen peroxide using a set of titanosilicate catalysts with different morphologies and textural properties&mdash, conventional titanium silicalite 1 (TS-1), mesoporous TS-1, layered TS-1 and silica-titania pillared TS-1 and also studying the effect of the solvent used. Epoxidation of C6=C7 double bond was the main primary reaction in this system and trace signals of C5 allylic oxidation products were observed without formation of citronellal. Due to the presence of post-synthesis introduced additional Ti sites, the silica-titania pillared TS-1 (TS-1-PITi) provided the highest conversion among the tested catalysts, nevertheless, citronellol was oxidized over all the studied catalysts including conventional TS-1, therefore, showing that it penetrates even into MFI micropores (0.55 nm in diameter). When using acetonitrile as a solvent, the conversion was proportional to the titanium content of the catalyst. When studying the effect of the solvent, acetonitrile provided the highest epoxide selectivity (55%) while in methanol, 2-propanol and 1,4-dioxane, ring opening reactions caused epoxide decomposition.

International audience; Titanium silicalite 1 (TS-1) zeolite is an important selective oxidation catalyst. Recently prepared layered and pillared forms expanded the application of TS-1 to the catalytic oxidation of bulky molecules. Despite progress in designing and application of titanosilicate zeolites in catalysis, only qualitative information of their acidity is available. Herein, we report thorough characterization of acid sites in TS-1 zeolites of different morphologies (3D TS-1, layered 2D TS-1, 2D TS-1 pillared either with silica (TS-1-PISi) or silica-titania (TS-1-PITi)) using FTIR spectroscopy and probe molecules. FTIR of adsorbed pyridine was used for quantification of Ti-associated Lewis acid sites based on the integral intensity of υ8a absorption band ca. 1608 cm−1 and measured integrated molar extinction coefficient (ε1608(Ti-LAS) = 0.71 ± 0.01 cm μmol–1). Thermodesorption of pyridine monitored with FTIR showed that distribution of strength of Lewis acid sites is, to some extent, dependent on the way of Ti incorporation in the samples. TS-1-PITi, containing large fraction of external surface Ti(OH)(OSi)3 species introduced post-synthesis, showed increased concentration of stronger Lewis acid centres. FTIR spectroscopy of TS-1 with pre-adsorbed quinoline and d3-acetonitrile probe confirmed enhanced relative concentration of external Lewis acid sites in all layered TS-1 materials (28–38%) vs. 3D TS-1 (2%).

Research activities and recent developments in the area of three-dimensional zeolites and their two-dimensional analogues are reviewed. Zeolites are the most important industrial heterogeneous catalysts with numerous applications. However, they suffer from limited pore sizes not allowing penetration of sterically demanding molecules to their channel systems and to active sites. We briefly highlight here the synthesis, properties and catalytic potential of three-dimensional zeolites followed by a discussion of hierarchical zeolites combining micro- and mesoporosity. The final part is devoted to two-dimensional analogues developed recently. Novel bottom-up and top-down synthetic approaches for two-dimensional zeolites, their properties, and catalytic performances are thoroughly discussed in this review.

The incorporation of various metals into the zeolite framework creates opportunities for novel applications, especially in catalysis. The recently developed assembly-disassembly-organisation-reassembly (ADOR) strategy was used to prepare zeolites with IPC-2 (OKO) topology. The layered zeolite precursor (IPC-1P) was modified by incorporating various metals (Al, Zn, Sn, Zr, V, Fe, Hf, and Ti) using a stabilisation process. The resulting materials were characterised by X-ray powder diffraction (XRD), Ar adsorption, scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), inductively coupled plasma optical emission spectroscopy (ICP-OES), and diffuse reflectance UV-Vis spectroscopy (DR-UV-Vis). The acidity of Al-containing IPC-2 materials was assessed by acetonitrile and pyridine sorption followed by FT-IR spectroscopy, showing overall concentrations of acid sites of 0.863 mmol g−1 (acetonitrile) and 0.413 mmol g−1 (pyridine). Titanium containing IPC-2 was examined by selective oxidation of methylphenyl sulfide (MPS) to the corresponding sulfoxide (MPSO). Ti-IPC-2 provided a higher conversion than TS-1 after 60 min (30% and 18% respectively) and showed higher selectivity towards MPSO (77% and 63% respectively). Sn-IPC-2 was tested by Baeyer–Villiger oxidation of norcamphor with aqueous hydrogen peroxide, showing a 3.8% norcamphor conversion and a 1.3% yield of the desired lactone (after 8 h reaction). Therefore, the results reported herein clearly show the successful incorporation of metals into the IPC-2 zeolite framework.

This review article aims to cover the state-of-the-art of titanosilicate catalysts for selective oxidations developed within past seven years. Many elaborated materials (e.g., layered and pillared ...

The Baeyer–Villiger oxidation is an important transformation of ketones into esters and particularly for cyclic ketones to lactones. We report here preparation and catalytic activity of layered Sn–silicate catalysts and mesoporous ordered silica catalysts in this reaction. Sn was introduced by using so-called tin–silica pillaring or by impregnation with a mixture of tetraethylorthosilicate and tin(IV) alkoxide. The prepared catalysts were characterized by XRD, N2 physisorption, SEM, UV/Vis, and inductively coupled plasma optical emission spectroscopy (ICP-OES) techniques and the catalysts were studied in the Baeyer–Villiger oxidation of cyclopentanone, norcamphor, and 2-adamantanone with aqueous hydrogen peroxide. Norcamphor and 2-adamantanone were oxidized easily with selectivity up to 99 %. Sn-MS and IPC-1-SnPI materials exhibited the highest conversions (e.g., norcamphor: Sn-MS 37 %, IPC-1-SnPI 36 % after 8 h vs. Sn-MCM-41 22 %). On the other hand, oxidation of cyclopentanone suffered from product hydrolysis to the corresponding 4-hydroxybutanoic acid.

Lamellar and pillared ZSM-5 materials modified with Mg and Zn oxides were synthesized and tested for in-situ catalytic upgrading of eucalyptus woodchips fast-pyrolysis vapors. The introduction of silica pillars into the lamellar ZSM-5 support led to a higher BET area, but also reduced the overall catalyst acidity. The incorporation of MgO and ZnO occurred with a high dispersion over the zeolitic supports, causing also a significant reduction in the value of their textural properties due to a partial blockage of the zeolite pores. Likewise, the acid features of the zeolitic supports underwent sharp changes by the addition of both MgO and ZnO with a strong decrease in the concentration of the Bronsted and Lewis acid sites present in the parent zeolite, as detected by pyridine adsorption followed FTIR spectroscopy. However, additional Lewis acid sites were created associated to the metal oxides deposited onto the zeolitic supports. Pyrolysis tests were accomplished using a lab-scale downdraft fixed-bed reactor working at atmospheric pressure and a temperature of 500 °C. The use of zeolitic catalysts increased the gas yield, mostly due to the formation of CO and CO 2 , to the detriment of bio-oil production. However, the so obtained bio-oils presented higher quality in terms of H/C and O/C ratios, and larger heating values. The incorporation of MgO and ZnO allowed tailoring the zeolite activity to avoid an excessive cracking of the bio-oil, which in turn resulted in a higher yield of the organic compounds present in the bio-oil, and decreasing the formation of undesired polyaromatic hydrocarbons and coke.

The UTL titanosilicate was prepared together with related lamellar Ti-IPC-1PISi material and zeolites Ti-IPC-2 (OKO) and Ti-IPC-4 (PCR) via top-down synthesis. The titanium can be incorporated to the UTL framework by conventional hydrothermal synthesis and it does not affect the so-called ADOR chemistry of the UTL material. Silica-titania pillaring concept was successfully applied providing very active Ti-IPC-1PITi catalyst for bulky molecules epoxidation with hydrogen peroxide. The textural properties of catalysts prepared can be tuned widely keeping the same crystalline titanosilicate active phase. All the materials were characterised by XRD, nitrogen sorption measurement, SEM, and DR-UV/vis spectroscopy. Ti-IPC-1PITi was the most active catalyst in cyclooctene, norbornene, and linalool epoxidation due to the lowest diffusion constraints and sufficient titanium content. Ti-UTL showed activity similar to Ti-BEA in epoxidation of cyclooctene and it provided different products than other titanosilicates in oxidation of linalool with hydrogen peroxide.

TS-1-based catalysts with different textural features, namely layered TS-1, pillared TS-1, and Ti-pillared TS-1 as well as mesoporous TS-1, were investigated in the liquid-phase epoxidation of methyl oleate as a model compound for plant oil-derived substrates with hydrogen peroxide at 50 °C. While over the TS-1-based catalysts, except Ti-pillared TS-1, an epoxide selectivity of up to 93% is achieved, layered and pillared TS-1 are the most active (the amounts of methyl oleate converted after 5 h per number of Ti-sites are 4.64 mol mol−1 and 4.68 mol mol−1) with an efficiency for H2O2 conversion to the epoxide of 27%. Mesoporous TS-1 and conventional microporous TS-1 exhibit a similar activity (3.64 mol mol−1vs. 3.37 mol mol−1), whereas the mesoporous catalyst most efficiently utilizes H2O2 (39% efficiency). The lowest catalytic activity (0.82 mol mol−1), epoxide selectivity as well as H2O2 efficiency are observed over Ti-MCM-36, possessing mainly octahedrally coordinated Ti-sites. The results demonstrate the importance of accessibility of Ti-sites at external crystal surfaces within layered and pillared TS-1, significantly increasing the epoxidation activity with respect to the number of Ti-atoms present in the catalysts.

Lamellar and pillared ZSM-5 zeolites (L-ZSM-5 and PI-ZSM-5, respectively) were synthesized and tested in the catalytic cracking of low-density polyethylene (LDPE). The introduction of silica pillars into lamellar ZSM-5 caused a high increase in the Si/Al ratio (from 33 up to 64) and the generation of uniform mesopores with a size of about 3.5 nm. Both samples provided quite similar LDPE conversions at the three reaction temperatures investigated (340, 360 and 380 °C) despite the lower concentration of acid sites in PI-ZSM-5, which is assigned to the improved active centre accessibility due to the pillaring treatment. Significant activity was observed even at the lowest temperature, with LDPE conversions in the range 27–36%, which indicates that 2D ZSM-5 zeolites are convenient catalysts for polyethylene cracking. The main products of LDPE catalytic cracking were C2–C5 olefins with a selectivity of 60–70%, denoting that an end-chain cracking mechanism is predominant. 2D ZSM-5 samples were subsequently compared with nanocrystalline (n-ZSM-5) and hierarchical ZSM-5 (h-ZSM-5) zeolites. Pyridine adsorption followed by FTIR measurements showed significant differences in terms of not only acid site concentration but also the Bronsted/Lewis acid distribution among the samples. When the LDPE cracking conversion was referred to the zeolite mesopore/external surface area, a good correlation was observed with the concentration of Bronsted acid sites but not when considering just the Lewis acid sites. This interesting fact suggests that Bronsted acid sites are mainly the active centers for the cracking of the LDPE chains, concluding that in addition to the accessibility, the nature of the acid sites plays a major role in this type of reaction.

The authors acknowledge the Czech Science Foundation (P106/12/G015) for the financial support. Selective oxidation of sulphides is a straightforward method of preparation of organic sulphoxides and sulphones, which are important chemical intermediates and building blocks of pharmaceuticals and agrochemicals. Oxidation of methylphenyl sulphide (MPS), diphenyl sulphide (Ph2S), and dibenzothiophene (DBTH) over lamellar titanosilicate catalysts with the MFI and UTL-derived topology was investigated with hydrogen peroxide as the oxidant. Lamellar titanosilicates combine the advantages of crystalline zeolites and mesoporous molecular sieves due to accessible active sites located on the external surface of their layers. The selectivity of the MPS oxidation to methylphenyl sulphoxide is driven by the diffusion restrictions in the catalyst. A methylphenyl sulphoxide selectivity of 95% at 40% conversion was achieved using the Ti-IPC-1-PI catalyst together with an outstanding TONtot = 1418 after 30 min. The selectivity can be adjusted also by dosing of the oxidant to keep its concentration low during the reaction. The silica-titania pillared TS-1-PITi catalyst showed the highest potential of the tested catalysts in oxidative desulphuration, easily oxidising the DBTH to dibenzothiothene sulphone. Postprint