Balancing the Kinetic and Thermodynamic Synergetic Effect of Doped Carbon Molecular Sieves for Selective Separation of C2H4/C2H6.

Selective separation of ethylene and ethane (C2H4/C2H6) is a formidable challenge due to their close molecular size and boiling point. Compared to industry-used cryogenic distillation, adsorption separation would offer a more energy-efficient solution when an efficient adsorbent is available. Herein, a class of C2H4/C2H6 separation adsorbents, doped carbon molecular sieves (d-CMSs) is reported which are prepared from the polymerization and subsequent carbonization of resorcinol, m-phenylenediamine, and formaldehyde in ethanol solution. The study demonstrated that the polymer precursor themselves can be a versatile platform for modifying the pore structure and surface functional groups of their derived d-CMSs. The high proportion of pores centered at 3.5 Å in d-CMSs contributes significantly to achieving a superior kinetic selectivity of 205 for C2H4/C2H6 separation. The generated pyrrolic-N and pyridinic-N functional sites in d-CMSs contribute to a remarkable elevation of Henry selectivity to 135 due to the enhancement of the surface polarity in d-CMSs. By balancing the synergistic effects of kinetics and thermodynamics, d-CMSs achieve efficient separation of C2H4/C2H6. Polymer-grade C2H4 of 99.71% purity can be achieved with 75% recovery using the devised d-CMSs as reflected in a two-bed vacuum swing adsorption simulation.

Deep Potential Molecular Dynamics Study of Propane Oxidative Dehydrogenation.

Oxidative dehydrogenation (ODH) of light alkanes is a key process in the oxidative conversion of alkanes to alkenes, oxygenated hydrocarbons, and COx (x = 1,2). Understanding the underlying mechanisms extensively is crucial to keep the ODH under control for target products, e.g., alkenes rather than COx, with minimal energy consumption, e.g., during the alkene production or maximal energy release, e.g., during combustion. In this work, deep potential (DP), a neural network atomic potential developed in recent years, was employed to conduct large-scale accurate reactive dynamic simulations. The model was trained on a sufficient data set obtained at the density functional theory level. The intricate reaction network was elucidated and organized in the form of a hierarchical network to demonstrate the key features of the ODH mechanisms, including the activation of propane and oxygen, the influence of propyl reaction pathways on the propene selectivity, and the role of rapid H2O2 decomposition for sustainable and efficient ODH reactions. The results indicate the more complex reaction mechanism of propane ODH than that of ethane ODH and are expected to provide insights in the ODH catalyst optimization. In addition, this work represents the first application of deep potential in the ODH mechanistic study and demonstrates the ample advantages of DP in the study of mechanism and dynamics of complex systems.

Boundary-Rich Carbon-Based Electrocatalysts with Manganese(II)-Coordinated Active Environment for Selective Synthesis of Hydrogen Peroxide.

Coordinated manganese (Mn) electrocatalysts owing to their electronic structure flexibility, non-toxic and earth abundant features are promising for electrocatalytic reactions. However, achieving selective hydrogen peroxide (H2 O2 ) production through two electron oxygen reduction (2e-ORR) is a challenge on Mn-centered catalysts. Targeting this goal, we report on the creation of a secondary Mn(II)-coordinated active environment with reactant enrichment effect on boundary-rich porous carbon-based electrocatalysts, which facilitates the selective and rapid synthesis of H2 O2 through 2e-ORR. The catalysts exhibit nearly 100 % Faradaic efficiency and H2 O2 productivity up to 15.1 mol gcat -1 h-1 at 0.1 V versus reversible hydrogen electrode, representing the record high activity for Mn-based electrocatalyst in H2 O2 electrosynthesis. Mechanistic studies reveal that the epoxide and hydroxyl groups surrounding Mn(II) centers improve spin state by modifying electronic properties and charge transfer, thus tailoring the adsorption strength of *OOH intermediate. Multiscale simulations reveal that the high-curvature boundaries facilitate oxygen (O2 ) adsorption and result in local O2 enrichment due to the enhanced interaction between carbon surface and O2 . These merits together ensure the efficient formation of H2 O2 with high local concentration, which can directly boost the tandem reaction of hydrolysis of benzonitrile to benzamide with nearly 100 % conversion rate and exclusive benzamide selectivity.

Hydrogen Spillover-Driven Dynamic Evolution and Migration of Iron Oxide for Structure Regulation of Versatile Magnetic Nanocatalysts.

Magnetic nanocatalysts with properties of easy recovery, induced heating, or magnetic levitation play a crucial role in advancing intelligent techniques. Herein, we report a method for the synthesis of versatile core-shell-type magnetic nanocatalysts through "noncontact" hydrogen spillover-driven reduction and migration of iron oxide with the assistance of Pd. In situ analysis techniques were applied to visualize the dynamic evolution of the magnetic nanocatalysts. Pd facilitates the dissociation of hydrogen molecules into activated H*, which then spills and thus drives the iron oxide reduction, gradual outward split, and migration through the carbonaceous shell. By controlling the evolution stage, nanocatalysts having diverse architectures including core-shell, split core-shell, or hollow type, each featuring Pd or PdFe loaded on the carbon shell, can be obtained. As a showcase, a magnetic nanocatalyst (Pd-loaded split core-shell) can hydrogenate crotonaldehyde to butanal (26 624 h-1 in TOF, ∼100% selectivity), outperforming reported Pd-based catalysts. This is due to the synergy of the enhanced local magnetothermal effect and the preferential adsorption of -C═C on Pd with a small d bandwidth. Another catalyst (PdFe-loaded split core-shell) also delivers a robust performance in phenylacetylene semihydrogenation (100% conversion, 97.5% selectivity) as PdFe may inhibit the overhydrogenation of -C═C. Importantly, not only Pd, other noble metals (e.g., Pt, Ru, and Au) also showed a similar property, revealing a general rule that hydrogen spillover drives the dynamic reduction, splitting, and migration of encapsulated nanosized iron oxide, resulting in diverse structures. This study would offer a structure-controllable fabrication of high-performance magnetic nanocatalysts for various applications.

Beyond the Selectivity-Capacity Trade-Off: Ultrathin Carbon Nanoplates with Easily Accessible Ultramicropores for High-Efficiency Propylene/Propane Separation.

Rapid and highly efficient C3H6/C3H8 separation over porous carbons is seriously hindered by the trade-off effect between adsorption capacity and selectivity. Here, we report a new type of porous carbon nanoplate (CNP) featuring an ultrathin thickness of around 8 nm and easily accessible ultramicropores (approximately 5.0 Å). The ultrathin nature of the material allows a high accessibility of gas molecules into the interior transport channels, and ultramicropores magnify the difference in diffusion behavior between C3H6 and C3H8 molecules, together ensuring a remarkable C3H6/C3H8 separation performance. The CNPs show a high and steady C3H6 capacity of up to 3.03 mmol g-1 at 298 K during consecutive dynamic cycles, which is superior to that of the state-of-the-art porous carbons and even porous crystalline materials. In particular, the CNPs show a rapid gas diffusivity, which is 1000 times higher than that of conventional activated carbons. This research provides a promising design principle for addressing the selectivity-capacity trade-off for other types of adsorbent materials.

Boosting Selective Oxidation of Ethylene to Ethylene Glycol Assisted by In situ Generated H2 O2 from O2 Electroreduction.

Ethylene glycol is a useful organic compound and chemical intermediate for manufacturing various commodity chemicals of industrial importance. Nevertheless, the production of ethylene glycol in a green and safe manner is still a long-standing challenge. Here, we established an integrated, efficient pathway for oxidizing ethylene into ethylene glycol. Mesoporous carbon catalyst produces H2 O2 , and titanium silicalite-1 catalyst would subsequently oxidize ethylene into ethylene glycol with the in situ generated H2 O2 . This tandem route presents a remarkable activity, i.e., 86 % H2 O2 conversion with 99 % ethylene glycol selectivity and 51.48 mmol gecat -1 h-1 production rate at 0.4 V vs. reversible hydrogen electrode. Apart from generated H2 O2 as an oxidant, there exists ⋅OOH intermediate which could omit the step of absorbing and dissociating H2 O2 over titanium silicalite-1, showing faster reaction kinetics compared to the ex situ one. This work not only provides a new idea for yielding ethylene glycol but also demonstrates the superior of in situ generated H2 O2 in tandem route.

Oxidative dehydrogenation of light alkanes to olefins on metal-free catalysts.

Metal-free boron- and carbon-based catalysts have shown both great fundamental and practical value in oxidative dehydrogenation (ODH) of light alkanes. In particular, boron-based catalysts show a superior selectivity toward olefins, excellent stability and atom-economy to valuable carbon-based products by minimizing CO2 emission, which are highly promising in future industrialization. The carbonaceous catalysts also exhibited impressive behavior in the ODH of light alkanes helped along by surface oxygen-containing functional groups. This review surveyed and compared the preparation methods of the boron- and carbon-based catalysts and their characterization, their performance in the ODH of light alkanes, and the mechanistic issues of the ODH including the identification of the possible active sites and the exploration of the underlying mechanisms. We discussed different boron-based materials and established versatile methodologies for the investigation of active sites and reaction mechanisms. We also elaborated on the similarities and differences in catalytic and kinetic behaviors, and reaction mechanisms between boron- and carbon-based metal-free materials. A perspective of the potential issues of metal-free ODH catalytic systems in terms of their rational design and their synergy with reactor engineering was sketched.

Self-Pillared Ultramicroporous Carbon Nanoplates for Selective Separation of CH4 /N2.

There is growing evidence that pillaring up a densely packed ultramicroporous two-dimensional (2D) structure is an effective strategy to reduce their internal diffusion. Reliable pillaring paradigms, however, is rather challenging. Here we report a one-pot multi-component sequential assembly method for the preparation of a new self-pillared 2D polymer and ultramicroporous carbon with integrated surface protrusions. The molecular level pillaring process is surprisingly fast, that is, in 10 min. The thickness of nanoplate edge and the density (roughness), angle as well as height of protrusions can be precisely tuned. Exemplified in coal bed methane purification/separation, this unique pillared 2D carbons exhibit a CH4 /N2 selectivity up to 24 at a low CH4 partial pressure and two orders of magnitude faster CH4 diffusion kinetics than the commercial carbon molecular sieves. This solution synthesis methodology is generalizable for creation and fine tuning of pillared 2D heterostructures.

Plasma Tuning Local Environment of Hexagonal Boron Nitride for Oxidative Dehydrogenation of Propane.

Hexagonal boron nitride (h-BN) has lately received great attention in the oxidative dehydrogenation (ODH) reaction of propane to propylene for its extraordinary olefin selectivity in contrast to metal oxides. However, high crystallinity of commercial h-BN and elusive cognition of active sites hindered the enhancement of utilization efficiency. Herein, four kinds of plasmas (N2 , O2 , H2 , Ar) were accordingly employed to regulate the local chemical environment of h-BN. N2 -treated BN exhibited a remarkable activity, i.e., 26.0 % propane conversion with 89.4 % selectivity toward olefins at 520 °C. Spectroscopy demonstrated that "three-boron center" N-defects in the catalyst played a pivotal role in facilitating the conversion of propane. While the sintering effect of the "BOx " species in O2 -treated BN, led to the suppressed catalytic performance (12.4 % conversion at 520 °C).

Wiggling Mesopores Kinetically Amplify the Adsorptive Separation of Propylene/Propane.

Adsorptive separation is an appealing technology for propylene and propane separation; however, the challenge lies in the design of efficient adsorbents which can distinguish the two molecules having very similar properties. Here we report a kinetically amplified separation by creating wiggling mesopores in structurally robust carbon monoliths. The wiggling mesopores with alternating wide and narrow segments afford a surface area of 413 m2 g-1 and a tri-modal pore size distribution centered at 1.5, 4.2 and 6.6 nm, respectively. The synergistically kinetic and equilibrium effects were observed and quantitatively assessed, which together ensured a remarkable propylene/propane selectivity up to 39. This selectivity outperformed not only the available carbon adsorbents but also highly competitive among the dominated crystalline porous adsorbents. In addition, the wiggling mesoporous carbon adsorbent showed excellent dynamical separation stability, which ensured its great potential in practical molecular separations.

A Mechanochemical-Assisted Synthesis of Boron, Nitrogen Co-Doped Porous Carbons as Metal-Free Catalysts.

A green and convenient solid-state method assisted by mechanical energy is employed for the synthesis of boron (B) and nitrogen (N) co-doped porous carbons (B,N-Cs). Glutamic acid (Glu) and boric acid (H3 BO3 ) are used as the N-containing carbon precursor and boron source, respectively. This method is easy to perform and proved to be efficient towards co-doping B and N into the carbon matrix with high contents of B (7 atom %) and N (10 atom %). By adjusting the molar ratio of H3 BO3 to Glu, the surface chemical states of B and N could be readily modulated. When increasing H3 BO3 dosage, the pore size of B,N-Cs could be tuned ranging from micropores to mesopores with a Brunauer-Emmett-Teller (BET) surface area up to 940 m2 g-1 . Finally, the B,N-Cs were applied as metal-free catalysts for the cycloaddition of CO2 to epoxides, which outperform the N-doped carbon catalyst (NC-900) and the physically mixed catalyst of NC-900/B4 C. The enhanced activity is attributed to the cooperative effect between B and N sites. X-ray photoelectron spectroscopy (XPS) analysis reveals that BN3 in the B,N-Cs serves as a critical active site for the cooperative catalysis.

Molecular-Based Design of Microporous Carbon Nanosheets.

Microporous carbons afford high surface areas, large pore volumes, and good conductivity, and are fascinating over a wide range of applications. Traditionally synthesized microporous carbon materials usually suffer from some limitations, such as poor accessibility and slow mass transport of molecules due to the micrometer-scale diffusion pathways and space confinement imposed by small pore sizes. Two-dimensional microporous carbon materials, denoted as microporous carbon nanosheets (MCNs), possess nanoscale thickness, which allows fast mass and heat transport along the z axis; thus overcoming the drawbacks of their bulk counterparts. Herein, recent breakthroughs in the synthetic strategies for MCNs are summarized. Three typical methods are discussed in detail with several examples: pyrolysis of organic precursors with 2D units, a templating method that uses wet chemistry, and the molten salt method. Among them, molecular-based assembly of MCNs in the liquid phase shows more controllable morphology, thickness, and pore size distribution. Finally, challenges in this research area are discussed to inspire future explorations.

Polyacrylonitrile-Derived Sponge-Like Micro/Macroporous Carbon for Selective CO2 Separation.

CO2 capture under a dynamical flow situation requires adsorbents possessing balanced proportion of macropores as diffusion path and micropores as adsorption reservoir. However, the construction of interconnected micro-/macropores structure coupled with abundant nitrogen species into one carbon skeleton remains a challenge. Here, we report a new approach to prepare sponge-like carbon with a well-developed micro-/macroporous structure and enriched nitrogen species through aqueous phase polymerization of acrylonitrile in the presence of graphene oxide. The tension stress caused by the uniform thermal shrinkage of polyacrylonitrile during the pyrolysis together with the favorable flexibility of graphene oxide sheets are responsible for the formation of the sponge-like morphology. The synergistic effect of micro-/macroporous framework and rich CO2 -philic site enables such carbon to decrease resistance to mass transfer and show high CO2 dynamic selectivity over N2 (454) and CH4 (11), as well as good CO2 capacity at 298 K under low CO2 partial pressure (0.17 bar, a typical CO2 partial pressure in flue gas). The above attributes make this porous carbon a promising candidate for CO2 capture from flue gas, methane sources and other relevant applications.

Thermoregulated Phase-Transition Synthesis of Two-Dimensional Carbon Nanoplates Rich in sp2 Carbon and Unimodal Ultramicropores for Kinetic Gas Separation.

The development of highly selective, chemically stable and moisture-resistant adsorbents is a key milestone for gas separation. Porous carbons featured with random orientation and cross-linking of turbostratic nanodomains usually have a wide distribution of micropores. Here we have developed a thermoregulated phase-transition-assisted synthesis of carbon nanoplates with more than 80 % sp2 carbon, unimodal ultramicropore and a controllable thickness. The thin structure allows oriented growth of carbon crystallites, and stacking of crystallites in nearly parallel orientation are responsible for the single size of the micropores. When used for gas separation from CH4 , carbon nanoplates exhibit high uptakes (5.2, 5.3 and 5.1 mmol g-1 ) and selectivities (7, 71 and 386) for CO2 , C2 H6 and C3 H8 under ambient conditions. The dynamic adsorption capacities are close to equilibrium uptakes of single components, further demonstrating superiority of carbon nanoplates in terms of selectivity and sorption kinetics.

Using hollow carbon nanospheres as a light-induced free radical generator to overcome chemotherapy resistance.

Under evolutionary pressure from chemotherapy, cancer cells develop resistance characteristics such as a low redox state, which eventually leads to treatment failures. An attractive option for combatting resistance is producing a high concentration of produced free radicals in situ. Here, we report the production and use of dispersible hollow carbon nanospheres (HCSs) as a novel platform for delivering the drug doxorubicine (DOX) and generating additional cellular reactive oxygen species using near-infrared laser irradiation. These irradiated HCSs catalyzed sufficiently persistent free radicals to produce a large number of heat shock factor-1 protein homotrimers, thereby suppressing the activation and function of resistance-related genes. Laser irradiation also promoted the release of DOX from lysosomal DOX@HCSs into the cytoplasm so that it could enter cell nuclei. As a result, DOX@HCSs reduced the resistance of human breast cancer cells (MCF-7/ADR) to DOX through the synergy among photothermal effects, increased generation of free radicals, and chemotherapy with the aid of laser irradiation. HCSs can provide a unique and versatile platform for combatting chemotherapy-resistant cancer cells. These findings provide new clinical strategies and insights for the treatment of resistant cancers.

Evidence of Microporous Carbon Nanosheets Showing Fast Kinetics in both Gas Phase and Liquid Phase Environments.

Despite the great advantages of microporous carbons for applications in gas phase separation, liquid phase enrichment, and energy storage devices, direct experiment data and theoretical calculations on the relevance of properties and structures are quite limited. Herein, two model carbon materials are designed and synthesized, i.e., microporous carbon nanosheets (MCN) and microporous carbon spheres (MCS). They both have nearly same composition, surface chemistry, and specific surface area, known morphology, but distinguishable diffusion paths. Based on these two types of materials, a reliable relationship between the morphology with different diffusion paths and adsorption kinetics in both gas phase and liquid phase environments is established. When used for CO2 capture, MCN shows a high saturated CO2 capacity of 8.52 µmol m(-2) and 18.4 mmol cm(-3) at 273 K and ambient pressure, and its calculated first-order rate constant is ≈7.4 times higher than that of MCS. Moreover, MCN shows a quick and high uptake of Cr (VI) and a higher-rate performance for supercapacitors than MCS does. These results strongly confirm that MCN exhibits improved kinetics in gas phase separation, liquid phase enrichment, and energy storage devices due to its shorter diffusion paths and larger exposed geometrical area resulting from the nanosheet structure.

Porous carbon anodes for a high capacity lithium-ion battery obtained by incorporating silica into benzoxazine during polymerization.

Porous carbon anodes with a controllable Vmes/Vmic ratio were synthesized through the self-assembly of poly(benzoxazine-co-resol) and the simultaneous hydrolysis of tetraethyl orthosilicate (TEOS) followed by carbonization and removal of silica. The Vmes/Vmic ratio of the carbon can be controlled in the range of approximately 1.3-32.6 through tuning the amount of TEOS. For lithium-ion battery anodes, a correlation between the electrochemical performance and Vmes/Vmic ratio has been established. A high Vmes/Vmic ratio in porous carbons is favorable for enhancing the accessibility of Li ions to active sites provided by the micropores and for achieving good lithium storage performance. The obtained porous carbon exhibits a high reversible capacity of 660 mAh g(-1) after 70 cycles at a current density of 100 mA g(-1). Moreover, at a high current density of 3000 mA g(-1), the capacity still remains at 215 mAh g(-1), showing a fast charge-discharge potential. This synthesis method relying on modified benzoxazine chemistry with the hydrolysis of TEOS may provide a new route for the development of mesoporous carbon-based electrode materials.

Al2O3 Nanosheets Rich in Pentacoordinate Al(3+) Ions Stabilize Pt-Sn Clusters for Propane Dehydrogenation.

In heterogeneous catalysis, supports play a crucial role in modulating the geometric and electronic structure of the active metal phase for optimizing the catalytic performance. A γ-Al2O3 nanosheet that contains 27% pentacoordinate Al(3+) sites can nicely disperse and stabilize raft-like Pt-Sn clusters as a result of strong interactions between metal and support. Consequently, there are strong electronic interactions between the Pt and Sn atoms, resulting in an increase in the electron density of the Pt sites. When used in the propane dehydrogenation reaction, this catalyst displayed an excellent specific activity for propylene formation with >99% selectivity, and superior anti-coking and anti-sintering properties. Its exceptional ability to maintain the high activity and stability at ultrahigh space velocities further showed that the sheet construction of the catalyst facilitated the kinetic transfer process.

Selective formation of carbon-coated, metastable amorphous ZnSnO3 nanocubes containing mesopores for use as high-capacity lithium-ion battery.

Mesoporous and amorphous ZnSnO3 nanocubes of ~37 nm size coated with a thin porous carbon layer have been prepared using monodisperse ZnSn(OH)6 as the active precursor and low-temperature synthesized polydopamine as the carbon precursor. The small single nanocubes cross-link with each other to form a continuous conductive framework and interconnected porous channels with macropores of 74 nm width. Because of its multi-featured nanostructure, this material exhibits greatly enhanced integration of reversible alloying/de-alloying (i.e., transformation of Li(4.4)Sn and LiZn to Sn and Zn) and conversion (i.e., oxidation of Sn and Zn to ZnSnO3) reaction processes with an extremely high capacity of 1060 mA h g(-1) for up to 100 cycles. A high reversible capacity of 650 and 380 mA h g(-1) can also be delivered at rates of 2 and 3 A g(-1), respectively. This excellent electrochemical performance is attributed to the small particle size, well-developed mesoporosity, the amorphous nature of the ZnSnO3 and the continuous conductive framework produced by the interconnected carbon layers.

Confined nanospace pyrolysis for the fabrication of coaxial Fe3O4@C hollow particles with a penetrated mesochannel as a superior anode for Li-ion batteries.

In this study, a method is developed to fabricate Fe3O4@C particles with a coaxial and penetrated hollow mesochannel based on the concept of "confined nanospace pyrolysis". The synthesis involves the production of a polydopamine coating followed by a silica coating on a rod-shaped ß-FeOOH nanoparticle, and subsequent treatment by using confined nanospace pyrolysis and silica removal procedures. Typical coaxial hollow Fe3O4@C possesses a rice-grain morphology and mesoporous structure with a large specific surface area, as well as a continuous and flexible carbon shell. Electrochemical tests reveal that the hollow Fe3O4@C with an open-ended nanostructure delivers a high specific capacity (ca. 864 mA h g(-1) at 1 A g(-1)), excellent rate capability with a capacity of about 582 mA h g(-1) at 2 A g(-1), and a high Coulombic efficiency (>97%). The excellent electrochemical performance benefits from the hollow cavity with an inner diameter of 18 nm and a flexible carbon shell that can accommodate the volume change of the Fe3O4 during the lithium insertion/extraction processes as well as the large specific surface area and open inner cavity to facilitate the rapid diffusion of lithium ions from electrolyte to active material. This fabrication strategy can be used to generate a hollow or porous metal oxide structure for high-performance Li-ion batteries.