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Sheet silicates, also known as phyllosilicates, contain parallel sheets of tetrahedral silicate built up by [Si2O5]2− entities connected through intermediate metal–oxygen octahedral layers. The well-known minerals talc and pyrophyllite are belonging to this group based on magnesium and aluminium, respectively. Surprisingly, the ferric analogue rarely occurs in nature and is found in mixtures and conglomerates with other materials only. While partial incorporation of iron into pyrophyllites has been achieved, no synthetic protocol for purely iron-based pyrophyllite has been published yet. Here we report about the first artificial synthesis of ferripyrophyllite under exceptional mild conditions. A similar ultrathin two-dimensional (2D) nanosheet morphology is obtained as in talc or pyrophyllite but with iron(III) as a central metal. The high surface material exhibits a remarkably high thermostability. It shows some catalytic activity in ammonia synthesis and can serve as catalyst support material for noble metal nanoparticles. [ABSTRACT FROM AUTHOR]

A series of SN1-type reactions has been studied under various conditions to clarify the role of supercritical carbon dioxide (scCO2) as reaction medium for this kind of transformations. The application of scCO2 did not result in higher yields in any of the experiments in comparison to those under neat conditions or in the presence of other inert compressed gases. High-pressure UV/Vis spectroscopic measurements were carried out to quantify the degree of carbocation formation of a highly SN1-active alkyl halide as a function of the applied solvent. No measureable concentration of carbocations could be detected in scCO2, just like in other low polarity solvents. Taken together, these results do not support the previously claimed activating effect via enhanced SN1 ionization due to the quadrupolar moment of the supercritical fluid. [ABSTRACT FROM AUTHOR]

The preparation, characterization, and catalytic properties of Pd nanoparticles supported on mesoporous organic–inorganic hybrid materials are described for continuous-flow aerobic oxidation of alcohols using supercritical carbon dioxide (scCO2) as a mobile phase. The nanoparticles were generated “bottom-up” from molecular precursors that were precoordinated to the support through suitable anchor units. The most active material allows high single-pass conversions in scCO2 at temperatures as low as 60 °C. This high activity may be associated with the presence of small primary crystallites (approx. 2 nm) that conglomerate to ensembles about 25 nm in size, leading to a larger number of high-indexed planes in small volume units. These findings may provide useful guidelines for further catalyst design on the nanoscale for green oxidation methods. [Copyright &y& Elsevier]

Temperature-responsive ionic liquids (ILs), their fundanmental behaviors, and catalytic applications were introduced, especially the concepts of upper critical solution temperature (UCST) and lower critical solution temperature (LCST). It is described that, during a catalytic reaction, they form a homogeneous mixture with the reactants and products at reaction temperature but separate from them afterward at ambient conditions. It is shown that this behavior offers an effective alternative approach to overcome gas/liquid-solid interface mass transfer limitations in many catalytic transformations. It should be noted that IL-based thermomorphic systems are rarely elaborated until now, especially in the field of catalytic applications. The aim of this article is to provide a comprehensive review about thermomorphic mixtures of an IL with H2O and/or organic compounds. Special focus is laid on their temperature dependence concerning UCST and LCST behavior, including systems with conventional ILs, metal-containing ILs, polymerized ILs, as well as the thermomorphic behavior induced via host-guest complexation. A wide range of applications using thermoregulated IL systems in chemical catalytic reactions as well as enzymatic catalysis were also demonstrated in detail. The conclusion is drawn that, due to their highly attractive behavior, thermoregulated ILs have already and will find more applications, not only in catalysis but also in other areas. [ABSTRACT FROM AUTHOR]

The selective hydrogenation of fluorinated arenes with polar functionalities is achieved, opening a versatile pathway for the production of valuable substituted fluorocyclohexane derivatives from readily available substrates. The use of supercritical carbon dioxide (scCO2) as a hydrophobic and green solvent in combination with Rh nanoparticles immobilized on molecularly modified silica as catalysts favours hydrogenation over hydrodefluorination. The approach compares favourably in terms of green chemistry metrics relative to traditional synthetic routes as exemplified for the useful building block 4-fluorocyclohexan-1-ol. [ABSTRACT FROM AUTHOR]

The fractionation of lignocellulose in its three main components, hemicellulose, lignin and cellulose pulp can be achieved in a biphasic system comprising water and bio-based 2-methyltetrahydrofuran (2-MeTHF) as solvents and oxalic acid as catalyst at mild temperatures (up to 140 °C). This so-called OrganoCat concept relies on selective hemicellulose depolymerization to form an aqueous stream of the corresponding carbohydrates, whereas solid cellulose pulp remains suspended and the disentangled lignin is to a large extent extracted in situ with the organic phase. In the present paper, it is demonstrated that biomass loadings of 100 g L−1 can be efficiently fractionated within 3 h whereby the mild conditions assure that no significant amounts of by-products (e.g. furans) are formed. Removing the solid pulp by filtration allows to re-use the water and organic phase without product separation in repetitive batch mode. In this way, (at least) 400 g L−1 biomass can be processed in 4 cycles, leading to greatly improved biomass-to-catalyst and biomass-to-solvent ratios. Economic analysis of the process reveals that the improved biomass loading significantly reduces capital and energy costs in the solvent recycle, indicating the importance of process integration for potential implementation. The procedure was successfully scaled-up from the screening on bench scale to 3 L reactor. The feedstock flexibility was assessed for biomasses containing moderate-to-high hemicellulose content. [ABSTRACT FROM AUTHOR]

Correction for ‘Fractionation of lignocellulosic biomass using the OrganoCat process’ by Philipp M. Grande et al., Green Chem., 2015, 17, 3533–3539. [ABSTRACT FROM AUTHOR]

Highlights: [•] The combination of zwitterion and phosphotungstate constructed a catalyst. [•] The combined catalyst exhibited high TON and TOF values for expoxidation. [•] The epoxidation can be performed under solventless and ice bath conditions. [•] Strong cooperative effect existed between zwitterions and phosphotungstate. [•] The formation of W/O emulsion by the zwitterion facilitated the reaction. [ABSTRACT FROM AUTHOR]

Magnetically separable catalysts were prepared and employed for the epoxidation of olefins with hydrogen peroxide. In all cases the magnetic core was firstly covered with a silica layer to prevent iron ion-initiated decomposition of hydrogen peroxide. The catalytic active species, an ionic liquid-type peroxotungstate, was then immobilized either by hydrogen bonding (catalyst 1) or by covalent SiO linkage (catalyst 2). In addition to a thorough characterization by FT-IR, XRD, NMR, DRIFT, XPS, and TEM, the catalytic potential was evaluated in the epoxidation of a variety of olefins as well as allylic alcohols. Both catalysts showed essentially a constant activity after at least ten consecutive cycles. On the basis of the research above, a new type of magnetically separable catalyst was constructed by immobilization of lacunary-type phosphotungstate by hydrogen bonding between the sulfonate anion and silanol group on the surface of the core-shell magnetic nanoparticles. After the detailed characterization, the catalyst was used in the epoxidation of a variety of olefins and allylic alcohols and was found to possess high activity, selectivity towards epoxides, and a constant activity after at least ten catalytic recycles without solvent. [ABSTRACT FROM AUTHOR]