The lack of chemical understanding and efficient catalysts impedes the development of electrocatalytic nitrogen reduction reaction (eNRR) for ammonia production. In this work, we employed density ...functional theory calculations to build up a picture (activity trends, electronic origins, and design strategies) of single-atom catalysts (SACs) supported on nitrogen-doped carbons as eNRR electrocatalysts. To construct such a picture, this work presents systematic studies of the eNRR activity of SACs covering 20 different transition metal (TM) centers coordinated by nitrogen atoms contained in three types of nitrogen-doped carbon substrates, which gives 60 SACs. Our study shows that the intrinsic activity trends could be established on the basis of the nitrogen adatom adsorption energy (ΔE N*). Furthermore, the influence of metal and support (ligands) on ΔE N* proved to be related to the bonding/antibonding orbital population and regulating the scaling relations for adsorption of intermediates, respectively. Accordingly, a two-step strategy is proposed for improving the eNNR activity of TM-SACs, which involves the following: (i) selection of the most promising family of SACs (g-C3N4 supported SACs as predicted in this work) and (ii) further improvement of the activity of the best candidate in the aforementioned family via tuning the adsorption strength of the key intermediates. Also, the stability of N-doped carbon supports and their selectivity in comparison to the competing hydrogen evolution need to be taken into consideration for screening the durable and efficient candidates. Finally, an effective strategy for designing active, stable, and selective SACs based on the mechanistic insights is elaborated to guide future eNRR studies.
A copper‐catalyzed asymmetric radical oxytrifluoromethylation of alkenyl oxime and Togni's reagent has been successfully developed, thereby providing straightforward access to CF3‐containing ...isoxazolines bearing α‐tertiary stereocenters with excellent yield and enantioselectivity. The key to success is the rational design of cinchona‐alkaloid‐based sulfonamides as neutral/anionic hybrid ligands to effectively control the stereochemistry in copper‐catalyzed reactions involving free alkyl radical species. The utility of this method is illustrated by efficient transformation of the products into useful chiral CF3‐containing 1,3‐aminoalcohols.
Powerful hybrid ligand: Cinchona‐alkaloid‐based sulfonamides were designed as effective hybrid ligands for copper, which enabled catalytic asymmetric radical oxytrifluoromethylation of alkenyl oximes to give CF3‐containing isoxazolines bearing α‐tertiary stereocenters with excellent yield and enantioselectivity.
Nanostructured Fe-N-C materials represent a new type of "platinum-like" non-noble-metal catalyst for various electrochemical reactions and organic transformations. However, no consensus has been ...reached on the active sites of the Fe-N-C catalysts because of their heterogeneity in particle size and composition. In this contribution, we have successfully prepared atomically dispersed Fe-N-C catalyst, which exhibited high activity and excellent reusability for the selective oxidation of the C-H bond. A wide scope of substrates, including aromatic, heterocyclic, and aliphatic alkanes, were smoothly oxidized at room temperature, and the selectivity of corresponding products reached as high as 99%. By using sub-ångström-resolution HAADF-STEM in combination with XPS, XAS, ESR, and Mössbauer spectroscopy, we have provided solid evidence that Fe is exclusively dispersed as single atoms via forming FeNx (x = 4-6) and that the relative concentration of each FeNx species is critically dependent on the pyrolysis temperature. Among them, the medium-spin FeIIIN5 affords the highest turnover frequency (6455 h-1), which is at least 1 order of magnitude more active than the high-spin and low-spin FeIIIN6 structures and 3 times more active than the FeIIN4 structure, although its relative concentration in the catalysts is much lower than that of the FeIIIN6 structures.
A novel radical 1,2‐formylfunctionalization of alkenes involving 1,2(4,5)‐formyl migration triggered by addition of various carbon‐ and heteroatom‐centered radicals to alkenes has been developed for ...the first time, thus providing straightforward access to diverse β‐functionalized aldehydes with good efficiency, remarkable selectivity, and excellent functional group tolerance. Analogous transformations mediated by a keto‐carbonyl migration have also been effected under similar conditions. This method was used to access ring systems including various benzannulated nine‐, ten‐, and eleven‐membered rings, complex 6‐5(6,7)‐6(5) fused rings, and bridged rings with diverse functionalities.
The old 1,2: A novel 1,2‐formyl functionalization of unactivated alkenes involving formyl migration and addition of radicals to alkenes has been developed for access to synthetically important β‐functionalized aldehydes. The analogous keto‐carbonyl migration has been performed to synthesize challenging medium‐sized diketones, which were additionally transformed into complex fused rings.
For high-temperature catalytic reaction, it is of significant importance and challenge to construct stable active sites in catalysts. Herein, we report the construction of sufficient and stable ...copper clusters in the copper‒ceria catalyst with high Cu loading (15 wt.%) for the high-temperature reverse water gas shift (RWGS) reaction. Under very harsh working conditions, the ceria nanorods suffered a partial sintering, on which the 2D and 3D copper clusters were formed. This partially sintered catalyst exhibits unmatched activity and excellent durability at high temperature. The interaction between the copper and ceria ensures the copper clusters stably anchored on the surface of ceria. Abundant in situ generated and consumed surface oxygen vacancies form synergistic effect with adjacent copper clusters to promote the reaction process. This work investigates the structure-function relation of the catalyst with sintered and inhomogeneous structure and explores the potential application of the sintered catalyst in C1 chemistry.
Display omitted
•Ultrasonic frequency, intensity, and duration affect algal cell disruption.•Acoustic cavitation, heat, pressure and free radicals are the major mechanisms.•Hybrid techniques of ...ultrasound and other disruption methods reduce energy cost.•Target product release is a vital indicator to reflect cell disruption degree.•Researches on system design and quality control for commercial use are needed.
Microalgae are a promising feedstock for the production of biofuels, nutraceuticals, pharmaceuticals and cosmetics, due to their superior capability of converting solar energy and CO2 into lipids, proteins, and other valuable bioactive compounds. To facilitate the release of these important biomolecules from microalgae, effective cell disruption is usually necessary, where the use of ultrasound has gained tremendous interests as an alternative to traditional methods. This review not only summarizes the mechanisms of and operation parameters affecting cell disruption, but also takes an insight into measuring techniques, synergistic integration with other disruption methods, and challenges of ultrasonication for microalgal biorefining. Optimal conditions including ultrasonic frequency, intensity, and duration, and liquid viscosity and sonochemical reactor are the key factors for maximizing the disruption and extraction efficiency. A combination of ultrasound with other disruption methods such as ozonation, microwave, homogenization, enzymatic lysis, and solvents facilitates cell disruption and release of target compounds, thus provides powerful solutions to commercial scale-up of ultrasound extraction for microalgal biorefining. It is concluded that ultrasonication is a sustainable “green” process, but more research and work are needed to upscale this process without sacrificing performance or consuming more energy.
This paper first establishes the index system of high-quality economic development and realizes the calculation of economic high-quality development score with the help of the entropy value method ...and coupling mechanism. Secondly, by constructing a spatial autocorrelation model, the spatial spillover effect of new infrastructure on high-quality economic development is empirically investigated. The mediation effect of digital new infrastructure on economic high-quality development through industrial structure and technological progress is continued to be analyzed. Finally, based on the panel data of 30 Chinese provinces from 2008 to 2020, the dynamic panel threshold model and the dynamic spatial Durbin model are used to test the nonlinear effects of financial resource allocation on the convergence of high-quality economic development and the mechanism of action, respectively. It is found that the direct effect coefficient of digital new infrastructure is 0.002 with a p-value less than 5%, and the indirect effect coefficient is 0.004, which passes the significance test at the 1% level. It is conducive to promoting high-quality economic development, and the allocation of financial resources can significantly enhance the role of new digital infrastructure in promoting high-quality economic development. Accordingly, implementing the new digital infrastructure proposed in this paper has contributed to the modernization of government governance, optimized the allocation of financial resources, and promoted high-quality economic development.
In this paper, we first study the representation of news text, build the content tree using the CTWE text method, and combine the word vector with the interrelationship between words in the content ...tree. Then, a feature word extraction technique is applied to filter key information, and Single-pass hierarchical clustering algorithm is used to classify the news content, and a data mining algorithm is applied to realize news delivery. Finally, the impact of information’s initial value and credibility on the transmission process is examined, and the model’s feasibility and practicality are assessed. The results show that the RMSE value of the data mining model is 0.0408, the Pearson correlation coefficient is 0.9334, and the cosine similarity is 0.9596, and the model in this paper has the smallest deviation from the real data and the greatest similarity compared with other models. This study confirms the unique advantages of the data mining model in news dissemination.
Wealth is often seen as an object of desire. That is, it is what desire desires and it comes to represent desire. The accumulation of wealth is commonly considered excessive and coming at the cost of ...environmental and corporeal needs. Such an account of wealth follows an either/or logic that produces a set of oppositional terms such as nature or culture, desire or need, wealth or necessity, luxury or survival. This article explores questions of wealth and desire via the 2018 film Crazy Rich Asians. It uses the lens of ornament to zoom in on how the film depicts the relationship between the natural and the artificial, winning and losing, and subject and object. It proposes a feminist ornamental approach to wealth and desire that reworks the either/or logic and the oppositional terms that undergird it. It argues that this approach allows for an analysis of the relation between race, gender, nature, style, wealth and desire beyond one of commodification or recognition, ownership or dispossession.
An asymmetric intermolecular, three-component radical-initiated dicarbofunctionalization of 1,1-diarylalkenes with diverse carbon-centered radical precursors and electron-rich heteroaromatics by a ...copper(I) and chiral phosphoric acid cooperative catalysis strategy has been developed, providing straightforward access to chiral triarylmethanes bearing quaternary all-carbon stereocenters with high efficiency as well as excellent chemo- and enantioselectivity. The key to success is not only the introduction of a sterically demanding chiral phosphoric acid to favor radical difunctionalization over the otherwise remarkable side reactions but also the in situ generation of carbocation intermediates from benzylic radical to realize asymmetric induction with the aid of a removable hydroxy directing group via cooperative interactions with chiral phosphate. Density functional theory calculations elucidated the critical chiral environment created by the hydrogen-bonding and ion-pair interactions between the chiral phosphoric acid catalyst and substrates, which leads to the enantioselective C–C bond formation.
PDF
