An overview of recent advances of the catalytic selective oxidation of ethane to oxygenates

The selective partial oxidation of short chain alkanes is a key challenge within catalysis research. Direct ethane oxidation to oxygenates is a difficult aim, but potentially rewarding, and it could lead to a paradigm shift in the supply chain of several bulk chemicals. Unfortunately, low C–H bond reactivity and kinetically labile products are just some reasons affecting the development and commercialisation of such processes. Research into direct ethane oxidation is therefore disparate, with approaches ranging from oxidation in the gas phase at high temperatures to enzyme catalysed hydroxylation under ambient conditions. Furthermore, in overcoming the barrier posed by the chemically inert C–H bond a range of oxidants have been utilised. Despite years of research, this remains an intriguing topic from both academic and commercial perspectives. Herein we describe some recent developments within the field of catalytic ethane oxidation focusing on the formation of oxygenated products, whilst addressing the key challenges which are still to be overcome

The design of new catalysts for the partial oxidation of methane to methanol.

The direct partial oxidation of CH4 to CH30H would offer considerable economic advantages over the current two stage process. It would also facilitate the utilisation of natural gas reserves in remote locations. To date, the catalytic partial oxidation of CH4 to CH30H has been extensively studied, however, it has proved to be an extremely demanding reaction which has met with little success. This study has adopted a design approach for the identification of new catalysts by considering the efficacy of single oxides for CH4 activation, CH30H oxidation and 02 isotope exchange activity. On the basis of CH30H stability Sb203 was the best oxide, showing only 3 % CH30H conversion at 500°C. The majority of oxides totally combusted CH30H below 400°C. Mo03, Nb20S, Ta20S and W03 showed high selectivity to HCHO and (CH3hO with low levels of COx throughout the range of conversion. These oxides were not considered unsuitable from the perspective of CH30H stability as the products HCHO and (CH3hO are not considered undesirable by products from a CH4 partial oxidation process. A weak but significant correlation was observed between the combustion activity of the oxides and the oxygen exchange rate. Using CH4/D2 exchange as an indication of CH4 activation it has been shown that Ga203 was a particularly good catalyst, followed by ZnO and Cr203. A relationship between exchange activity and oxide basicity was established for the rare earth sesquioxides, MgO and CaO. This relationship indicak:d that CH4 activation took place by H+ abstraction to form a surface CH3- species. From these results and literature studies of oxygen isotope exchange, dual component oxides have been formulated as catalysts for CH4 partial oxidation. The best catalysts was Ga203/Mo03, prepared by a physical mixing process. This catalyst showed an increased yield of CH30H over the homogeneous gas phase oxidation of CH4 in a quartz chips packed reactor. This increased yield has been attributed to the development of a cooperative effect between the two component oxides. Comparison of the catalytic data with the homogeneous reaction in the empty reactor tube showed that the presence of a catalyst had a detrimental effect on the CH30H yield

Nanoporous aluminosilicate-catalyzed telescoped acetalization-direct aldol reactions of acetals with 1,3-dicarbonyl compounds

Nanoporous aluminosilicate materials, synthesized by an evaporation-induced self-assembly process, catalyze the direct aldol reaction of acyclic acetals with a range of 1,3-dicarbonyl compounds to produce the corresponding aldol addition products in high yield, rather than the expected Knoevenagel elimination products. By carrying out the reaction in the presence of either dimethoxy propane or the corresponding orthoester, it is possible to capitalize on the ability of these aluminosilicate materials to catalyze the corresponding acetalization reaction leading to the development of novel telescoped, acetalization-direct aldol addition reaction protocols

Study of the magnetite to maghemite transition using microwave permittivity and permeability measurements

The microwave cavity perturbation (MCP) technique is used to identify the transition from magnetite (Fe3O4) to the meta-stable form of maghemite (γ-Fe2O3). In this study Fe3O4 was annealed at temperatures from 60 to 300 °C to vary the oxidation. Subsequent to annealing, the complex permittivity and magnetic permeability of the iron oxide powders were measured. The transition to γ-Fe2O3 was corroborated with x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometry (VSM). XRD, XPS and VSM implied that the starting powder was consistent with Fe3O4 and the powders annealed at more than 200 °C were transitioning to γ-Fe2O3. The MCP measurements gave large differences in both complex permittivity and magnetic permeability of the two phases in the frequency range of 2.5–10.2 GHz. Magnetic permeability decreased with annealing temperature, though magnetic losses showed frequency dependent behaviour. Complex permittivity measurements showed a large decrease in both dielectric constant and losses at all measurement frequencies, as well as a prominent loss peak centred around the phase transition temperatures. We interpret the loss peak as being a consequence of field effects due to an intermediate multi-phase mixture. Additionally, almost no frequency dependence was observed. The reduction in complex permittivity implies that the $\text{Fe}_{\text{oct}}^{2+}$ cations in the lattice provide a significant contribution to polarization at microwave frequencies and the effects of $\text{Fe}_{\text{oct}}^{3+}$ are nominal in comparison. The change in loss can be explained as a combination of the differences in the effective conductivity of the two phases (i.e. Fe3O4 exhibits electron-hopping conduction whereas the presence of vacancies in γ-Fe2O3 nullifies this). This shows that the non-invasive MCP measurements serve as a highly sensitive and versatile method for looking at this phase transition in iron and potentially the effects of oxidation states on the polarization in other iron oxides

The selective oxidation of n-butanol to butyraldehyde by oxygen using stable Pt-based nanoparticulate catalysts: an efficient route for upgrading aqueous biobutanol

Supported Pt nanoparticles are shown to be active and selective towards butyraldehyde in the base-free oxidation of n-butanol by O2 in an aqueous phase. The formation of butyric acid as a by-product promoted the leaching of Pt and consequently the activity of the catalysts decreased upon reuse. Characterisation showed that the degree to which Pt leached from the catalysts was related to both the metal–support interaction and metal particle size. A catalyst active and stable (<1% metal leaching) in the aqueous reaction medium was obtained when Pt nanoparticles were supported on activated carbon and prepared by a chemical vapour impregnation method. The presence of n-butanol in the aqueous medium is required to inhibit the over oxidation of butyraldehyde to butyric acid. Consequently, high selectivities towards butyraldehyde can only be obtained at intermediate n-butanol conversion

Dehydrative etherification reactions of glycerol with alcohols catalyzed by recyclable nanoporous aluminosilicates: telescoped routes to glyceryl ethers

Catalytic strategies for the efficient transformation of abundant sustainable bioderived molecules, such as glycerol, into higher value more useful products is an important research goal. In this study, we demonstrate that atom efficient dehydrative etherification reactions of glycerol with activated alcohols are effectively catalyzed by nanoporous aluminosilicate materials in dimethylcarbonate (DMC) to produce the corresponding 1-substituted glyceryl ethers in high yield. By carrying out the reaction in acetone, it is possible to capitalize on the ability of these materials to catalyze the corresponding acetalization reaction, allowing for the development of novel, telescoped acetalization-dehydrative etherification reaction sequences to selectively produce protected solketal derivatives. These materials also catalyze the telescoped reaction of glycerol with <i>tert</i>-butanol (TBA) in acetone to produce the corresponding solketal mono <i>tert</i>-butyl ether product in high yield, providing a potential route to convert glycerol directly into a useful and sustainable fuel additive

One-step production of 1,3-butadiene from 2,3-butanediol dehydration

We report the direct production of 1,3-butadiene from the dehydration of 2,3-butandiol by using alumina as a catalyst. Under optimized kinetic reaction conditions, the production of methyl ethyl ketone and isobutyraldehyde, formed via the pinacol-pinacolone rearrangement, was markedly reduced and over 80% selectivity to 1,3-butadiene and 3-buten-2-ol could be achieved. The presence of water plays a critical role in the inhibition of oligomerization.The amphoteric nature of ϒ- Al2O3 was identified as important and this contributed to the improved catalytic selectivity when compared with other acidic catalysts

The role of copper speciation in the low temperature oxidative upgrading of short chain alkanes over Cu/ZSM-5 catalysts

Partial oxidative upgrading of C1–C3 alkanes over Cu/ZSM‐5 catalysts prepared by chemical vapour impregnation (CVI) has been studied. The undoped ZSM‐5 support is itself able to catalyse selective oxidations, for example, methane to methanol, using mild reaction conditions and the green oxidant H2O2. Addition of Cu suppresses secondary oxidation reactions, affording methanol selectivities of up to 97 %. Characterisation studies attribute this ability to population of specific Cu sites below the level of total exchange (Cu/Al<0.5). These species also show activity for radical‐based methane oxidation, with productivities exceeding those of the parent zeolite supports. When tested for ethane and propane oxidation reactions, comparable trends are observe