Despite the large number of disparate approaches for the direct selective partial oxidation of methane, none of them has translated into an industrial process. The oxidation of methane to methanol is ...a difficult, but intriguing and rewarding, task as it has the potential to eliminate the prevalent natural gas flaring by providing novel routes to its valorization. This Review considers the synthesis of methanol and methanol derivatives from methane by homogeneous and heterogeneous pathways. By establishing the severe limitations related to the direct catalytic synthesis of methanol from methane, we highlight the vastly superior performance of systems which produce methanol derivatives or incorporate specific measures, such as the use of multicomponent catalysts to stabilize methanol. We thereby identify methanol protection as being indispensable for future research on homogeneous and heterogeneous catalysis.
Being selective: The selective oxidation of methane to methanol in high yield is currently elusive, but when accomplished it could redefine the petrochemical industry. This Review illustrates the homogeneous and heterogeneous catalytic routes for this process and discerns the most promising approaches with the potential to conquer the challenge.
Lewis acidic aluminum in zeolites, particularly acidity that is inherent to the framework, is an indeterminate concept. A fraction of framework aluminum changes geometry to octahedral coordination in ...the proton form of zeolite mordenite. Such octahedrally coordinated aluminum is the precursor of a Lewis acid site and its formation is accompanied by a loss in Brønsted acidity. Herein, we show that such Lewis acid sites have a preferred location in the pore structure of mordenite. A greater proportion of these Lewis acid sites resides in the side-pockets than in the main channel. By reverting the octahedrally coordinated aluminum back to a tetrahedral geometry, the corresponding Brønsted acid sites are restored with a concomitant loss in the ability to form Lewis acid sites. Thereby, reversible octahedral-tetrahedral aluminum coordination provides a means to indirectly switch between Lewis and Brønsted acidity. This phenomenon is unique to Lewis acidity that is inherent to the framework, thereby distinguishing it from Lewis acidity originating from extra-framework species. Furthermore, the transformation of framework aluminum into octahedral coordination is decoupled from the generation of distorted tetrahedrally coordinated aluminum, where the latter gives rise to the IR band at 3660 cm
−1
in the OH stretching region.
Framework-associated aluminum is demonstrated to facilitate a reversible switch between Lewis and Brønsted acidity in zeolites with the Lewis acid sites preferentially populating the side-pockets in the case of mordenite.
Rapid industrialization, modern agricultural practices and other anthropogenic activities add a significant quantity of toxic heavy metals into the environment, which induces severe toxic effects on ...all form of living organisms, alter the soil properties and its biological activity. Remediation of heavy metal contaminated sites has become an urgent necessity. Among the existing strategies, phytoremediation is an eco-friendly and much convincing tool for the remediation of heavy metals. However, the applicability of phytoremediation in contaminated sites is restricted by two prime factors such as i) slow growth rate at higher metal contaminated sites and ii) metal bioavailability. This circumstance could be minimized and accelerate the phytoremediation efficiency by incorporating the potential plant growth promoting rhizobacterial (PGPR) as a combined approach. PGPR inoculation might improve the plant growth through the production of plant growth promoting substances and improve the heavy metal remediation efficiency by the secretion of chelating agents, acidification and redox changes. Moreover, rhizobacterial inoculation consolidates the metal tolerance and uptake by regulating the expression of various metal transporters, tolerant and metal chelator genes. However, the exact underlying molecular mechanism of PGPR mediated plant growth promotion and phytoremediation of heavy metals is poorly understood. Thus, the present review provides clear information about the molecular mechanisms excreted by PGPR strains in plant growth promotion and phytoremediation of heavy metals.
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•Specific and non-specific plant growth promoting mechanisms of the PGPR strains elucidated.•The role of PGPR strains in phytoextraction, phytostabilization and phytovolatilization has been brought forward.•Possible molecular mechanism behind PGPR assisted phytoremediation has been illustrated.
A promising strategy to break through the selectivity‐conversion limit of direct methane conversion to achieve high yields is the protection of methanol via esterification to a more stable methyl ...ester. We present an aerobic methane‐to‐methyl‐ester approach that utilizes a highly dispersed, cobalt‐containing solid catalyst, along with significantly more favorable reaction conditions compared to existing homogeneously‐catalyzed approaches (e.g. diluted acid, O2 oxidant, moderate temperature and pressure). The trifluoroacetic acid medium is diluted (<25 wt %) with an inert fluorous co‐solvent that can be recovered after the separation of the methyl trifluoroacetate via liquid–liquid extraction at ambient conditions. Silica‐supported cobalt catalysts are highly active in this system, with competitive yields and turnovers in comparison to known aerobic transition metal‐based catalytic systems.
Methane is aerobically converted to an oxidation‐resistant methyl ester in high yields with a solid cobalt‐containing catalyst at a moderate temperature and pressure. Improved reaction conditions result from the dilution of the trifluoroacetic acid in an inert perfluoroalkane co‐solvent. The fluorous character of the solvent enables the facile recovery of the product ester through a simple liquid‐liquid extraction with non‐fluorous solvent.
Amidst ongoing attempts to enhance green chemistry education in the chemical sciences curriculum, the teaching of analytical methods, such as spectroscopy, still largely lacks grounding in the ...principles of green chemistry. In an attempt to embed this context to spectroscopy education, this article describes the development, delivery, and evaluation of a course module designed to teach spectroscopic methods within the context of pollution analysis. Using the Integrated Course Design framework, a course section that intertwines fundamental spectroscopy knowledge with the application to pollution analysis was developed. Following the design and delivery of diverse teaching and learning activities, the analysis of student feedback revealed a high degree of satisfaction with the course. Some reservations around digital learning resources and group work activities present scope for improvement. This paper also describes the use of a multifold student assessment model developed on the basis of spaced repetition learning.
A scale-flexible process for the direct and selective oxidation of methane to primary oxygenates is of great interest, however, a commercially feasible approach has yet to be realized due to a number ...of challenges. Low product yields imposed by a well-established selectivity-conversion limit are particularly burdensome for direct methane-to-methanol chemistry. One strategy that has emerged to break out of this limit is the
esterification of produced methanol to the more oxidation-resistant methyl ester. However, these methaneto-methyl-ester approaches still elude commercialization despite their unprecedented high yields. Herein, we outline some of the key barriers that hinder the commercial prospects of this otherwise promising route for highyield direct catalytic methane conversion, including extremely corrosive reagents, homogeneous catalysts, and inviable oxidants. We then highlight directions to address these challenges while maintaining the characteristic high performance of these systems. These discussions support the efficacy of product protection strategies for the direct, selective oxidation of methane and encourage future work in developing creative solutions to merge this promising chemistry with more practical industrial requirements.
Alongside innovation in teaching practice, student assessment in chemical engineering has seen significant changes in the recent past. This article undertakes a systematic review of the recent ...advances that have been reported in assessment practice in chemical engineering education. The main trends that emerge are: a shift towards authentic assessment methods, an increase in emphasis on peer-assessment and other approaches for group-based assignments, and a greater use of digital tools for the delivery of authentic assessments and improvement of marking and feedback practice. The analysis also examines the diversity of assessment methods used across the different chemical engineering subjects and how these map against assessment frameworks reported in the wider pedagogical literature. The emerging strand of research on synoptic and interdisciplinary assessment is used to develop an assessment framework for producing chemical engineering graduates who are also socially responsible and competent global citizens.
•Diverse authentic assessment methods reported in chemical engineering education.•Design, modeling and simulation have the greatest use of authentic assessment.•Increased digitalization for assessment authenticity, feedback and peer-assessment.•Synoptic and interdisciplinary assessments constitute more recent developments.
The objective of this prospective observational study was to assess the door-to-balloon time (D2B), in acute ST-segment elevation myocardial infarction (STEMI) patients and the time factors ...influencing it. The following timeframes were measured during the study: ED to ECG time, ED to coronary care unit time (ED2CCU), consent time, post-consent to balloon time (POSTCONSENT2B) and D2B. Effective D2B was 54 ± 12.2 min. Of the dependent variables, D2B had a strong positive correlation (ρ = 0.903) with consent time. This study sheds light on consent time a previously unrecognized entity as a significantly influencing factor for the D2B time.
Arsenic (As), a potent environmental toxin, causes cardiac functional impairments. Ferulic acid (FA), a ubiquitous dietary hydroxycinnamate, exerts beneficial effects on human health. Hence, the ...present study investigated the effect of FA on myocardial oxidative stress parameters, ATP level, the status of cardiac cytoskeleton intermediate filaments—desmin and vimentin, and AMPK signaling proteins in As‐intoxicated rats. Wistar rats were administered orally with FA‐40 mg/kg and As‐5 mg/kg alone and in combination for 30 days. Myocardial As content, serum cardiac marker enzyme activities including creatine kinase‐isoenzyme, lactate dehydrogenase, and aspartate aminotransferase were increased in As‐exposed rats. An accumulation of myocardial oxidants such as reactive oxygen species, lipid peroxidation, nitric oxide, protein carbonyl content, and histological aberrations was observed. A significant decrease of myocardial antioxidants comprises superoxide dismutase, catalase, glutathione peroxidase, reduced glutathione, and ascorbic acid and declined expression of desmin and vimentin was noted. Impaired energy signaling molecules AMPKα (Thr172), AMPKβ1/2 (Ser108), ACC (Ser79), and intracellular myocardial ATP depletion were observed in As‐intoxicated animals. FA attenuates As‐induced cardiac dysfunction by restoring the expression of intermediate filaments and AMPK proteins. Based on the above findings, FA treatment could be used as a novel therapeutic against As‐induced cardiac dysfunction.
Chromium (Cr) is a toxic heavy metal discharged into the environment through various anthropogenic sources, which affects soil properties and fertility. Hence, an effective soil restoration strategy ...is the need of the hour. In this study, a potent Cr(VI)-reducing strain M2 was isolated from the rhizosphere of Zea mays L. grown in leather industrial effluent contaminated sites and identified as Bacillus flexus through 16S rDNA sequencing. Strain M2 exhibited strong tolerance to multi-stresses such as temperature (up to 45 °C), pH (up to 9.0), Sodium chloride (NaCl) (up to 7%) and PEG 6000 (up to 50%) and showed strong Cr(VI) reduction with the presence of multi-stresses. The interaction of Cr(VI) with strain M2 was elucidated through various instrumentation analyses. Fourier Transform Infra-red (FTIR) Spectroscopy analysis confirmed that Cr(VI) exposures induce significant changes in the cell-surface functional groups. Raman spectrum and Transmission Electron Microscopy–Energy Dispersive X-ray spectroscopy (TEM-EDX) analysis confirmed the bio-reduction of Cr(VI) to Cr(III) and their intracellular localization as Cr(III). Further, strain M2 produced a significant quantity of Indole acetic acid (IAA), ammonia, and exopolysaccharide (EPS) and showed positive results for various plant-growth-promoting activities with the presence of Cr(VI). In greenhouse experiments, the strain M2 inoculation progressively increased the plant growth parameters and stabilized the antioxidant system of Vigna radiata under Cr stress. However, Cr(VI) exposure decreased the growth parameters and increased the level of proline content, Hydrogen peroxide (H2O2) accumulation, and antioxidant enzymes expression in V. radiata. Interestingly, strain M2 inoculation significantly reduced the accumulation of Cr in root and shoot of V. radiata when compared to the uninoculated Cr(VI) treatment. Hence, this study confirms that rhizobacterial inoculation markedly reduced the negative impact of Cr toxicity and improved V. radiata growth even in harsh environments by stabilizing the mobility of Cr in the rhizosphere.
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