In the recent years methane has become increasingly abundant. However, transportation costs are high and methane recovered as side product is often flared rather than valorized. The chemical ...utilization of methane is highly challenging and currently mainly based on the cost-intensive production of synthesis gas and its conversion. Alternative routes have been discovered in academia, though high temperatures are mostly required. However, the direct conversion of methane to methanol is an exception. It can already be carried out at comparably low temperatures. It is challenging that methanol is more prone to oxidation than methane, which makes high selectivities at moderate conversions difficult to reach. Decades of research for the direct reaction of methane and oxygen did not yield a satisfactory solution for the direct partial oxidation toward methanol. When changing the oxidant from oxygen to hydrogen peroxide, high selectivities can be reached at rather low conversions, but the cost of hydrogen peroxide is comparably high. However, major advancements in the field were introduced by converting methane to a more stable methanol precursor. Most notable is the conversion of methane to methyl bisulfate in the presence of a platinum catalyst. The reaction is carried out in 102% sulfuric acid using SO3 as the oxidant. This allows for oxidation of the platinum catalyst and prevents the in situ hydrolysis of methyl bisulfate toward the less stable methanol. With a slightly different motif, the stepped conversion of methane to methanol over copper-zeolites was developed a decade ago. The copper-zeolite is first activated in oxygen at 450 °C, and then cooled to 200 °C and reacts with methane in the absence of oxygen, thus protecting a methanol precursor from overoxidation. Subsequently methanol can be extracted with water. Several active copper-zeolites were found, and the active sites were identified and discussed. For a long time, the process was almost unchanged. Lately, we implemented online steam extraction rather than off-line extraction with liquid water, which enables execution of successive cycles. While recently we reported the isothermal conversion by employing higher methane pressures, carrying out the process according to prior art only yielded neglectable amounts of methane. Using a pressure <40 bar methane gave higher yields under isothermal conditions at 200 °C than most yields in prior reports. The yield, both after high temperature activation and under isothermal conditions at 200 °C, increased monotonously with the pressure. With this account we show that the trend can be represented by a Langmuir model. Thus, the pressure dependence is governed by methane adsorption. We show that the isothermal and the high temperature activated processes have different properties and should be treated independently, from both an experimental and a mechanistic point of view.
Here, we report the first direct amination of phenol with ammonia into primary anilines in the liquid phase. For this, Pd/C was demonstrated to be the most suitable catalyst. Optimization of the ...reaction parameters resulted in very selective and sustainable production of primary anilines with yields of up to 95%.
The concurrent hydrogenation of aromatic and nitro groups poses particular challenges due to the highly differing adsorption strengths of the two chemical moieties on the surfaces of metal catalysts. ...In a study of the hydrogenation of nitrobenzene as a model reaction, catalysts of ruthenium supported on carbon nanotubes (Ru/CNT) provided an ideal compromise, allowing for hydrogenation of both the aromatic ring and the nitro group. The use of methyl-labeled substrates enabled tracking the pathway of specific substrates and obtaining insight into the relative rates for the hydrogenation of nitrobenzene and intermediates. Together with findings on the coadsorption of nitrobenzene and aniline on the Ru/CNT catalyst, an advanced mechanistic model for the hydrogenation of nitrobenzene emerges.
The environmental impact of endocrine-disrupting chemicals (EDCs)—compounds that interfere with endocrine system function at minute concentrations—is now well established. In recent years, concern ...has been mounting over a group of endocrine disruptors known as hormonal growth promotants (HGPs), which are natural and synthetic chemicals used to promote growth in livestock by targeting the endocrine system. One of the most potent compounds to enter the environment as a result of HGP use is 17β-trenbolone, which has repeatedly been detected in aquatic habitats. Although recent research has revealed that 17β-trenbolone can interfere with mechanisms of sexual selection, its potential to impact sequential female mate choice remains unknown, as is true for all EDCs. To address this, we exposed female guppies (Poecilia reticulata) to 17β-trenbolone at an environmentally relevant level (average measured concentration: 2 ng/L) for 21 days using a flow-through system. We then compared the response of unexposed and exposed females to sequentially presented stimulus (i.e., unexposed) males that varied in their relative body area of orange pigmentation, as female guppies have a known preference for orange colouration in males. We found that, regardless of male orange pigmentation, both unexposed and exposed females associated with males indiscriminately during their first male encounter. However, during the second male presentation, unexposed females significantly reduced the amount of time they spent associating with low-orange males if they had previously encountered a high-orange male. Conversely, 17β-trenbolone-exposed females associated with males indiscriminately (i.e., regardless of orange colouration) during both their first and second male encounter, and, overall, associated with males significantly less than did unexposed females during both presentations. This is the first study to demonstrate altered sequential female mate choice resulting from exposure to an endocrine disruptor, highlighting the need for a greater understanding of how EDCs may impact complex mechanisms of sexual selection.
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•17β-trenbolone (TB) is a widespread agricultural contaminant used in cattle farming .•Female guppies were exposed to TB at an environmentally relevant level for 21 days.•TB altered sequential female mate choice in guppies.•Females exposed to TB associated with males less overall than unexposed females.•First study to show disruption of sequential female mate choice by exposure to an endocrine disruptor.
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•Phenol amination via cyclohexanone is possible in absence of added reductant.•Dehydrogenation of amine allows for hydrogenation of phenol and subsequent amination.•Nature of amine ...determines reactivity of the catalytic system.•Ease and possible extent of dehydrogenation of amine are important for reactivity.
Anilines and cyclohexylamines are currently produced from fossil feedstocks. Phenol would be an attractive alternative feedstock that can be obtained from renewable resources. We herein clarify the influence of the amine on the course of the amination of phenol using a hydrogen borrowing strategy. Amines can in this case act as a reductant which can be dehydrogenated to initiate the partial hydrogenation of phenol which is required for the reaction to take place. The nature of the amine reactant can have a larger effect than the presence of additional reductants like sodium formate. The results in this report do not only present a method for the amination of phenol without addition of an extra reductant, but also rationalize the reactivity of amines in their reaction with phenol.
Direct partial oxidation of methane into methanol is a cornerstone of catalysis. The stepped conversion of methane into methanol currently involves activation at high temperature and reaction with ...methane at decreased temperature, which limits applicability of the technique. The first implementation of copper‐containing zeolites in the production of methanol directly from methane is reported, using molecular oxygen under isothermal conditions at 200 °C. Copper‐exchanged zeolite is activated with oxygen, reacts with methane, and is subsequently extracted with steam in a repeated cyclic process. Methanol yield increases with methane pressure, enabling reactivity with less reactive oxidized copper species. It is possible to produce methanol over catalysts that were inactive in prior state of the art systems. Characterization of the activated catalyst at low temperature revealed that the active sites are small clusters of copper, and not necessarily di‐ or tricopper sites, indicating that catalysts can be designed with greater flexibility than formerly proposed.
Under pressure: Direct, stepped oxidation of methane into methanol was realized in an isothermal reaction. Otherwise inactive copper clusters were activated by employing higher methane pressures. This method provides new material design and process development opportunities that enable direct conversion of methane into methanol.
Despite a growing literature highlighting the potential impact of human-induced environmental change on mechanisms of sexual selection, relatively little is known about the effects of chemical ...pollutants on male-male competition. One class of environmental pollutant likely to impact male competitive interactions is the endocrine-disrupting chemicals (EDCs), a large and heterogeneous group of chemical contaminants with the potential to influence morphology, physiology and behaviour at minute concentrations. One EDC of increasing concern is the synthetic, androgenic steroid 17β-trenbolone, which is used globally to promote growth in beef cattle. Although 17β-trenbolone has been found to cause severe morphological and behavioural abnormalities in fish, its potential impact on male-male competition has yet to be investigated. To address this, we exposed wild male guppies (Poecilia reticulata) to an environmentally realistic concentration of 17β-trenbolone (average measured concentration: 8 ng/L) for 21 days using a flow-through system. We found that, in the presence of a competitor, 17β-trenbolone-exposed males carried out more frequent aggressive behaviours towards rival males than did unexposed males, as well as performing less courting behaviour and more sneak (i.e., coercive) mating attempts towards females. Considering that, by influencing mating outcomes, male-male competition has important consequences for population dynamics and broader evolutionary processes, this study highlights the need for greater understanding of the potential impact of EDCs on the mechanisms of sexual selection.
•17β-trenbolone (TB) is a widespread agricultural contaminant used in cattle farming.•Male guppies were exposed to TB at an environmentally relevant level for 21 days.•TB increased male aggression towards a rival and decreased courting of a female.•Males exposed to TB performed more ‘sneak’ mating attempts towards females.•First study to show disruption of male-male competition by exposure to TB.
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•Contamination of the environment with bioactive pharmaceuticals is a major problem.•We tested for impacts of the endocrine disruptor 17β-trenbolone (17β-TB) on male guppies.•Exposure ...altered male mating strategy when females were encountered sequentially.•Exposed males shifted towards a coercive ‘sneaking’ reproductive strategy.•Experience with a previous female was not found to affect male mating behaviour.
A leading source of endocrine-disrupting chemicals (EDCs) in the environment is run-off of veterinary pharmaceuticals used in agriculture, including hormonal growth promotants (HGPs). Despite being banned in various countries, HGP use is still common in beef production around the world. The androgenic steroid 17β-trenbolone (17β-TB) is a HGP that commonly enters surface waters via livestock effluent run-off. Here, we used a flow-through system to expose wild-caught adult male guppies (Poecilia reticulata) to an environmentally realistic level of 17β-TB (average measured concentration = 2 ng/L) for 21 days. We then compared the response of exposed and unexposed males to sequentially presented large and small stimulus (unexposed) females. Due to a positive size-fecundity relationship, larger females are generally expected to be preferred by males. While we found no evidence that the size of a previously encountered female affected the amount of courtship or coercive ‘sneak’ mating behaviour performed by males during the second presentation, males from both exposure treatments conducted more frequent courting events towards larger females during both presentations, suggesting an absolute preference for greater female size. Further, across both presentations, 17β-TB exposure caused a shift in male mating strategy towards increased coercive sneaking behaviour, although male sequential investment into mating effort was not impacted at the tested dosage. In combination, our findings demonstrate that exposure to a field-realistic level of a widespread agricultural pollutant alters male mating strategies in fish, and contribute to a growing understanding of sub-lethal impacts of chemical contaminants on complex behaviours in wildlife.
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•Hf and Zn combined showed good activity and selectivity to the desired products.•Hf-Zn/SiO2.Al2O3 displayed unprecedented stability compared with other systems.•Brønsted and Lewis ...acidity contributed to an active and selective catalyst.
A catalyst containing Hf4+ and Zn2+ supported on silica has been found to be highly effective for the synthesis of methylenedianiline (MDA), an indispensable precursor in the polyurethane industry. Its performance was further improved when the silica support was replaced by silica-alumina, which resulted in a catalyst that was both active and selective, as indicated by the high MDA yield and high 4,4′–MDA/(2,2′–MDA + 2,4′–MDA) isomer ratio obtained. Furthermore, the catalyst also gave an appreciable oligomeric MDA (OMDA) yield and was noticeably more stable than the zeolites that were used in comparative tests: it could be used in at least five consecutive runs without any significant loss in activity. The combination of Brønsted and Lewis acidity strongly increases the overall activity and yields a catalyst that represents a remarkably stable and reusable alternative to the commonly studied systems for this reaction.
Coke formation is the prime cause of catalyst deactivation, where undesired carbon wastes block the catalyst surface and hinder further reaction in a broad gamut of industrial chemical processes. ...Yet, the origins of coke formation and their distribution across the catalyst remain elusive, obstructing the design of coke‐resistant catalysts. Here, the first‐time application of tip‐enhanced Raman spectroscopy (TERS) is demonstrated as a nanoscale chemical probe to localize and identify coke deposits on a post‐mortem metal nanocatalyst. Monitoring coke at the nanoscale circumvents bulk averaging and reveals the local nature of coke with unmatched detail. The nature of coke is chemically diverse and ranges from nanocrystalline graphite to disordered and polymeric coke, even on a single nanoscale location of a top‐down nanoprinted SiO2‐supported Pt catalyst. Surprisingly, not all Pt is an equal producer of coke, where clear isolated coke “hotspots” are present non‐homogeneously on Pt which generate large amounts of disordered coke. After their formation, coke shifts to the support and undergoes long‐range transport on the surrounding SiO2 surface, where it becomes more graphitic. The presented results provide novel guidelines to selectively free‐up the coked metal surface at more mild rejuvenation conditions, thus securing the long‐term catalyst stability.
Coke formation is a prime cause of catalyst deactivation, where undesired carbon products block the catalytic active sites and impede further reaction. Herein, the nanofabrication of metal catalysts is synergized with advanced coke characterization via tip‐enhanced Raman spectroscopy. This approach reveals the chemical diversity of coke deposits at the nanoscale, opening novel routes for extending the catalyst's lifespan.
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