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Boron-containing materials have recently been identified as highly selective catalysts for the oxidative dehydrogenation (ODH) of alkanes to olefins. It has previously been demonstrated by several spectroscopic characterization techniques that the surface of these boron-containing ODH catalysts oxidize and hydrolyze under reaction conditions, forming an amorphous B(2)(OH)(2x)O((3 – x)) (x = 0 – 3) layer. Yet, the precise nature of the active site(s) remains elusive. In this communication, we provide a detailed characterization of zeolite MCM-22 isomorphously substituted with boron (B-MWW). Using (11)B solid-state NMR spectroscopy, we show that the majority of boron species in B-MWW exist as isolated BO(3) units, fully incorporated into the zeolite framework. However, this material shows no catalytic activity for ODH of propane to propene. The catalytic inactivity of B-MWW for ODH of propane falsifies the hypothesis that site-isolated BO(3) units are the active site in boron-based catalysts. This observation is at odds with other traditionally studied catalysts like vanadium-based catalysts and provides an important piece of the mechanistic puzzle.

The complexity of variables during incipient wetness impregnation synthesis of supported metal oxides precludes an in-depth understanding of the chemical reactions governing the formation of the dispersed oxide sites. This contribution describes the use of vapor phase deposition chemistry (also known as grafting) as a tool to systematically investigate the influence of isopropanol solvent on VO(Oi Pr)3 anchoring during synthesis of vanadium oxide on silica. The availability of anchoring sites on silica was found to depend not only on the pretreatment of the silica but also on the solvent present. H-bond donors can reduce the reactivity of isolated silanols whereas disruption of silanol nests by H-bond acceptors can turn unreactive H-bonded silanols into reactive anchoring sites. The model suggested here can inform improved syntheses with increased dispersion of metal oxides on silica.

Due to an increasing gap between the demand and supply, the catalytic coupling of ethanol has regained the attention of the scientific and industrial community as an "on-purpose" production route to butadiene. The most promising systems are based on bifunctional catalysts, comprising of metal sites that can dehydrogenate ethanol to acetaldehyde, and Lewis acid sites that catalyze the aldol condensation between two aldehyde molecules, as well as the Meerwein-Ponndorf-Verley (MPV) reduction of the intermediate crotonaldehyde. Here, we investigate the role of Ag in an established Ag-Zr-BEA catalyst using modulated operando DRIFTS-MS experiments. We obtain insights into the complex reaction network that involves several consecutive and parallel reactions. Based on our investigations, we formulate suggestions for catalyst optimization.

Hexagonal boron nitride (hBN) is presented as an outstanding catalyst for the selective production of C4 olefins by the oxidative dehydrogenation of n-butane and isobutane. Unlike catalysts reported previously, hBN limits the amount of undesired COx and instead forms C2 and C3 olefins as the main side products. Kinetic experiments suggest a mechanism in which the rates of n-butane and isobutane consumption are dependent on O2 adsorption. Kinetic and spectroscopic insights are used to formulate mechanistic hypotheses for the formation mechanisms of C2–C4 olefins.

Snβ zeolites are amongst the most effective heterogeneous catalysts for the Baeyer-Villiger (BV) oxidation of ketones with aqueous hydrogen peroxide (H2O2). The high selectivity is rooted in the activation of the carbonyl substrate through interaction with the isolated SnIV-sites. However, these sites are also accessible to other molecules in the reaction mixture (in particular the co-solvent and product). In this contribution, we report on the impact of competitive adsorption on the Snβ-catalyzed BV oxidation of cyclohexanone with aqueous H2O2. We furthermore prepared a series of Snβ zeolites with varying amounts of framework silanols and quantified their hydrophilicities with water adsorption and IR experiments. By correlating the results with catalytic data, we show that Snβ zeolites with an intermediate hydrophilicity achieve the highest activity. Our adaptable post-synthetic synthesis allows us to tune the material synthesis, resulting in enhanced activity compared to conventional hydrothermal Snβ.

The front cover artwork for Issue 20/2015 is provided by the Hermans research group at the University of Wisconsin-Madison (formerly located at the Swiss Federal Institute of Technology, Zurich). The image shows silica-supported Lewis acidic SnIV sites that are tuned to be catalytically active in the Meerwein–Ponndorf–Verley reduction of cyclohexanone with 2-butanol. See the Full Paper itself at http://dx.doi.org/10.1002/cctc.201500630.

Kupfer-ausgetauschte SSZ-13-Zeolithe sind sehr effiziente Materialien fur die selektive katalytische Reduktion von NOx mit Ammoniak (deNOx-SCR). Die Charakterisierung der Verteilung der Kupfer-Zentren in solchen Materialien ist von groster Bedeutung, um deren Aktivitat zu verstehen. In dieser Studie haben wir Infrarotspektren von NO adsorbiert an Kupfer-Zentren mittels Ab-initio-Molekulardynamiksimulationen modelliert. Fur die meisten Zentren haben wir komplexe Infrarotspektren mit mehreren Peaks gefunden, die durch thermische Bewegung der Kationen und der Adsorbate verursacht werden. Wir konstruierten ein Spektrum eines spezifischen Katalysators bei endlicher Temperatur, welches exzellent mit Literaturdaten ubereinstimmt. Die Resultate ermoglichen eine Zuordnung der aktiven und inaktiven Zentren fur die deNOx-SCR. Unseres Wissens ist dies die erste Arbeit, die uber solch komplexe Spektren fur einzelne adsorbierte Molekule an einzelnen aktiven Zentren in heterogenen Katalysatoren berichtet. Wir gehen davon aus, dass ahnliche Effekte auch in einer Vielzahl anderer Systeme mit beweglichen aktiven Zentren zu finden sind.

The abundant sesquiterpene β-caryophyllene can be epoxidized by molecular oxygen in the absence of any catalyst. In polar aprotic solvents, the reaction proceeds smoothly with epoxide selectivities exceeding 70 %. A mechanistic study has been performed and the possible involvement of free radical, spin inversion, and electron transfer mechanisms is evaluated using experimental and computational methods. The experimental data-including a detailed reaction product analysis, studies on reaction parameters, solvent effects, additives and an electrochemical investigation-all support that the spontaneous epoxidation of β-caryophyllene constitutes a rare case of unsensitized electron transfer from an olefin to triplet oxygen under mild conditions (80 °C, 1 bar O2 ). As initiation of the oxygenation reaction, the formation of a caryophyllene-derived radical cation via electron transfer is proposed. This radical cation reacts with triplet oxygen to a dioxetane via a chain mechanism with chain lengths exceeding 100 under optimized conditions. The dioxetane then acts as an in situ-formed epoxidizing agent. Under nitrogen atmosphere, the presence of a one-electron acceptor leads to the selective isomerization of β-caryophyllene to isocaryophyllene. Observations indicate that this isomerization reaction is a novel and elegant synthetic pathway to isocaryophyllene.

The homolytic scission of peroxides with catalytic amounts of cobalt(II) complexes is used in several industrial oxidation processes. In this contribution, we report that addition of small amounts of octanoic acid significantly enhances the catalytic deperoxidation activity of the cobalt(II)acetylacetonate complex. We attribute this to the stabilization of the Co--OOR bond upon coordination of octanoic acid, preventing the unimolecular scission. As such, the cobalt peroxo intermediate is forced to enter an alternative catalytic cycle which causes its rapid conversion to the highly reactive cobalt hydroxy. This shift in catalytic cycle results in a higher pre-exponential rate factor, over-compensating the higher barrier of the new rate-determining step.

TiCl4 grafted to dehydrated silica is an industrially applied catalyst for the epoxidation of propylene. As with many heterogeneous catalysts, the precise nature of the surface species is not yet fully known, prohibiting reliable structure-activity correlations. In this study, the speciation and restructuring of site-isolated Ti(IV) Lewis acid centers was carefully investigated by using a variety of techniques. The initially formed ≡SiOTiCl3 species were found to restructure upon heating through the transfer of Cl ligands to the silica surface, eventually leading to tripodal (≡SiO)3 TiCl species. The superior activity and stability of such tripodal species is demonstrated for catalytic olefin epoxidation under continuous flow conditions.

Homogeneous iridium catalysts have demonstrated exceptional catalytic activity for a number of hydrogen transfer reactions. Herein, we demonstrate the synthesis of a heterogeneous iridium catalyst supported on nanoparticulate cerium oxide and investigate its application for the aerobic oxidation of benzyl alcohol and the Meerwein–Ponndorf–Verley transfer hydrogenation of cyclohexanone. Along with the optimisation of the activity of the catalyst, the kinetic parameters have been examined to unravel the elementary reaction steps mediated by this catalyst and further rationalise the observed structure–activity relationships. Both spectroscopic and catalytic investigations suggest that iridium oxide nanoparticles, most likely Ir2O3, mediate these reactions via the formation of metal hydroxide species, which are subsequently reoxidised with either a molecular oxygen or a ketone. In contrast to many other metal- or metal oxide-based catalysts, this catalyst can perform the selective oxidation of alcohols in the absence of a base, at mild temperatures and at a low metal loading.

The homolytic cleavage of peroxide bonds, leading to the formation of free radicals, plays an important role in the (spontaneous) oxidation of a wide variety of hydrocarbons in the presence of oxygen. Such aerobic oxidations can be desired (e.g. for industrially applied autoxidations) or undesired (e.g. food deterioration). In this contribution we provide experimental and computational evidence for a molecule-induced homolytic dissociation mechanism between alkyl peroxide and compounds featuring weakly bonded H atoms such as (di)unsaturated hydrocarbons.

Sn einfach eingebaut: Ein einfaches und schnelles Verfahren fur die Synthese von Lewis-sauren Sn-β-Zeolithen wurde entwickelt (siehe Schema). Die Materialien sind katalytisch hochaktiv und ergeben in der Baeyer-Villiger-Oxidation von Cyclohexanon und der Synthese von Ethyllactat aus Dihydroxyaceton Raum-Zeit-Ausbeuten, die mehr als eine Grosenordnung uber den Werten konventioneller Katalysatoren liegen.

Tin goes in: The solid Lewis acid Sn-zeolite β is obtained in a simple and scalable procedure (see scheme). A high metal content can be obtained, without undesirable side-effects. The space-time-yields of the resulting catalysis are over one order-of-magnitude larger than those of the state-of-the-art materials for the Baeyer–Villiger oxidation of cyclohexanone and the synthesis of ethyl lactate from the triose dihydroxyacetone.

The economically viable oxidative upgrading of methane presents one of the most difficult but rewarding challenges within catalysis research. Its potential to revolutionalise the chemical value chain, coupled with the associated supremely challenging scientific aspects, has ensured this topic's high popularity over the preceeding decades. Herein, we report a non-exhaustive account of the current developments within the field of oxidative methane upgrading and summarise the pertaining challenges that have yet to be solved.

Molybdenum(VI)peroxide species, formed in the reaction of MoVI complexes with peroxides, are able to epoxidize >CC< double bonds heterolytically. In this study, theoretical and experimental evidence is provided for a kinetically competing reaction reaction of such molybdenum(VI)peroxide species with additional peroxide reagent, leading to molybdenum(VI)trioxide species, which easily decompose into radicals. Under epoxidation conditions, those radicals will reduce the selectivity, due to the formation of allylic byproducts. The involved reaction pathways are characterized by DFT calculations, providing kinetic parameters that are in good agreement with the experimental observations.

Herein we report a new, one-step procedure for the metal-free ketonization of unsaturated fatty acid methyl esters and triacylglycerol mixtures with nitrous oxide (N 2 O). The conversion of various substrates can be tuned by parameters such as temperature, reaction time and N 2 O partial pressure. This ketonization chemistry offers various advantages over the classic Wacker catalytic process and a state-of-the-art two-step procedure via intermediate epoxides.

In this work, a complementary experimental and theoretical approach is used to unravel the formation of byproducts in the autoxidation of cyclohexane. The widely accepted vision that cyclohexanone would be the most important precursor of undesired products was found inconsistent with several experimental observations. However, the propagation reaction of cyclohexyl hydroperoxide, which we recently put forward as the missing source of cyclohexanol and cyclohexanone, is now unambiguously identified also as the dominant path leading to byproducts. Indeed, this overlooked reaction produces large amounts of cyclohexoxy radicals, able to ring-open via a beta-C--C cleavage to omega-formyl radicals. The pathway by which these radicals are converted into the observed and quantified byproducts is derived in this work. In this liquid-phase reaction, solvent cages were found very important, steering the fate of nascent species.

Herein, we demonstrate that the chain-initiating dissociation of cyclohexyl hydroperoxide, CyOOH, is substantially accelerated by H-bond acceptors (e.g. Teflon), which assist O-O bond breaking by stabilising the leaving *OH radical. This is a completely new approach to boost the chain-propagating radical concentration. Indeed, up to now, literature has remained focussed on transition metal catalysis. In addition to this initiation effect, we demonstrate how inert perfluorinated compounds are also able to steer the selectivity at the molecular level, by promoting the conversion of the intermediate cyclohexyl hydroperoxide to the most desired end-product, cyclohexanone. This effect is explained by an enhanced, H-bond-assisted, hydroperoxide propagation. This hitherto overlooked hydroperoxide propagation was recently presented by us as the dominant cyclohexanone and cyclohexanol source. We herein thus confirm our previously reported autoxidation scheme, and illustrate its usefulness as a solid basis for designing new catalytic systems.

In spite of its industrial importance, the detailed reaction mechanism of cyclohexane autoxidation by O2 is still insufficiently known. Based on quantum chemical potential energy surfaces, rate coefficients of the primary and secondary chain propagation steps involving the cyclohexylperoxyl (CyOO) radical were evaluated using multiconformer transition-state theory. Including tunneling and hindered-internal-rotation effects, the rate coefficient for hydrogen-atom abstraction from cyclohexane (CyH) by CyOO was calculated to be k(T)= 1.46 x 10(-11) x exp(-17.8 kcal mol(-1)/ RT) cm3s(-1) (300-600K), close to the experimental data. A "Franck-Rabinowitch cage" reaction between the nascent cyclohexylhydroperoxide (CyOOH) and cyclohexyl radical, products from CyOO + CyH, is put forward as an initially important cyclohexanol (CyOH) formation channel. alphaH abstraction by CyOO. from cyclohexanone was calculated to be only about five times faster than that from CyH, too slow to explain all the observed side products. The a-hydrogen (alphaH) abstractions from CyOH and CyOOH by CyOO. are predicted to be about 10 and 40 times faster, respectively, than the CyOO. +CyH reaction. The very fast CyOO.+CyOOH reaction proceeds through the unstable Cy-alphaH .OOH radical that decomposes spontaneously into the ketone (Q=O) plus the OH radical; the "hot" .OH is found to produce the bulk of the alcohol via a second, "activated cage" reaction analogous to that above. It is thus shown how the very reactive CyOOH intermediate is the predominant source of ketone and alcohol, while it also leads to some side products. The alpha-hydroxycyclohexylperoxyl radical formed during the moderately fast oxidation of CyOH is shown to decompose fast into HO2 + cyclohexanone in a rapidly equilibrated reaction, which constitutes a smaller, second ketone source. These two fast cyclohexanone forming routes avoid the need for unfavorable molecular routes hitherto invoked as ketone sources. The theoretical predictions are supported and complemented by experimental findings. The newly proposed scheme is also largely applicable to the oxidation of other hydrocarbons, such as toluene, xylene, and ethylbenzene.

Boron nitride was recently identified as a highly selective catalyst for the oxidative dehydrogenation of propane (ODHP). In this communication we report that other boron-containing materials such as boron carbide, titanium boride, nickel boride, cobalt boride, hafnium boride and tungsten boride, as well as elemental boron itself show the same exceptional behavior as boron nitride. X-ray photoelectron and infrared spectroscopy suggest oxyfunctionalization of the surface. This observation disproves previous mechanistic hypotheses that edge sites on the boron nitride would be the active sites and rather suggests the formation of an analogous surface-stabilized BOx active site for all tested boride catalysts.

The oxidative upgrading of amines offers great opportunities for the sustainable production of key N-containing building-blocks for the modern chemical industry. Compared to other oxyfunctionalizations, and despite their potential, amine oxidation reactions are barely explored in the literature. This review aims at drawing attention to this important area and highlights both the major achievements and the challenges that still remain.

Functionalizing organic molecules is an important value-creating step throughout the entire chemical value-chain. Oxyfunctionalization of e.g. C-H or C=C bonds is one of the most important functionalization technologies used industrially. The major challenge in this field is the prevention of side reactions and/or the consecutive over-oxidation of the desired products. Despite its importance, a fundamental understanding of the intrinsic chemistry, and the subsequent design of a tailored engineering environment, is often missing. Industrial oxidation processes are indeed to a large extent based on empirical know-how. In this mini-review, we summarize some of our previous work to help to bridge this knowledge gap and elaborate on our ongoing research.

During the autoxidation of cyclohexane, abstraction of the αH-atom of the hydroperoxide product by chain-carrying peroxyl radicals produces both the desired alcohol and ketone products, as well as the majority of by-products. Rationalizing the impact of this reaction, one should aim for a (catalytic) destruction of this hydroperoxide without the intervention of peroxyl chain-carriers. Starting from these new insights in the molecular mechanism, attempts for rational catalyst design are initiated.

Der heterogene Katalysator Sn-β wird gegenwartig in einer komplizierten Hydrothermalsynthese hergestellt, die einige unuberwindbare Hurden bezuglich der industriellen Implementierung aufweist. In ihrer Zuschrift auf S. 11906 ff. berichten I. Hermans und Mitarbeiter uber die einfache Herstellung von Sn-β durch Ionenaustausch im Festkorper. Die Methode erfordert sehr viel weniger Zeit und Aufwand, und das Produkt ermoglicht um eine Grosenordnung hohere Raum-Zeit-Ausbeuten als bisherige Katalysatoren.

The heterogeneous catalyst Sn-β is currently prepared in a complicated hydrothermal synthesis, which has several hurdles that prevent its industrial implementation. In their Communication on page 11736 ff., I. Hermans and co-workers report a convenient preparation of Sn-β by solid-state ion exchange. It requires much less time and synthetic skill, and the product has more favorable catalytic properties, giving space–time yields over one order of magnitude higher than previously observed.