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To date, NH3synthesis under mild conditions is largely confined to precious Ru catalysts, while nonprecious metal (NPM) catalysts are confronted with the challenge of low catalytic activity due to the inverse relationship between the N2dissociation barrier and NHx(x= 1–3) desorption energy. Herein, we demonstrate NPM (Co, Ni, and Re)-mediated Mo2CTxMXene (where Txdenotes the OH group) to achieve efficient NH3synthesis under mild conditions. In particular, the NH3synthesis rate over Re/Mo2CTxand Ni/Mo2CTxcan reach 22.4 and 21.5 mmol g–1h–1at 400 °C and 1 MPa, respectively, higher than that of NPM-based catalysts and Cs–Ru/MgO ever reported. Experimental and theoretical studies reveal that Mo4+over Mo2CTxhas a strong ability for N2activation; thus, the rate-determining step is shifted from conventional N2dissociation to NH2* formation. NPM is mainly responsible for H2activation, and the high reactivity of spillover hydrogen and electron transfer from NPM to the N-rich Mo2CTxsurface can efficiently facilitate nitrogen hydrogenation and the subsequent desorption of NH3. With the synergistic effect of the dual active sites bridged by H-spillover, the NPM-mediated Mo2CTxcatalysts circumvent the major obstacle, making NH3synthesis under mild conditions efficient.

The hydrogenation of amides is an important but highly challenging reaction, which usually is applied under drastic conditions (temperature >160 °C). Here, we report a heterogeneous Pt–MoOx/TiO2catalyst for amide and imide hydrogenation under milder conditions. The catalytic reactivity is proposed to originate from the synergistic effect between surface active species. Pt promotes formation of partially reduced MoOxthat is responsible for CO activation, and MoOx-modified Pt can more efficiently generate surface species from gas-phase H2. This catalyst system enables the selective hydrogenation of several 2° and 3° amides as well as imides.

High-silica zeolite Y encapsulated ultra-small Ru nanoclusters enhance the catalytic selectivity and stability for the direct hydrodeoxygenation of neat methyl levulinate into pentanoic biofuels at a previously unattained reaction temperature.

Methanol with 12.5 wt% H2content is widely considered a liquid hydrogen medium. Taking into account water with 11.1 wt% H2content, H2synthesis from the mixture of water and methanol is a promising method for on-demand hydrogen production. We demonstrate an atomic-level catalyst design strategy using the synergy between single atoms and nanodots for H2production. The PtCu–TiO2sandwich photocatalyst achieves a remarkable H2formation rate (2,383.9 µmol h–1) with a high apparent quantum efficiency (99.2%). Furthermore, the oxidation product is a high-value chemical formaldehyde with 98.6% selectivity instead of CO2, leading to a nearly zero-carbon-emission process. Detailed investigations indicate a dual role of the copper atoms: an electron acceptor to facilitate photoelectron transfer to Pt, and a hole acceptor for the selective oxidation of methanol to formaldehyde, thus avoiding over-oxidation to CO2. The synergy between Pt nanodots and Cu single atoms together reduces the activation energy of this process to 13.2 kJ mol–1.

In this work, we identified the prevailing catalytically active species evolved from paired PdCl2–CuCl2in 1-butyl-3-methylimidazolium chloride ([BMim]Cl) that displayed dramatic synergy between the two metal chlorides in catalyzing the hydrolysis of β-1,4-glycosidic bonds in cellulose. Ultraviolet-visible (UV-vis), far infrared (FIR), and electron paramagnetic resonance (EPR) spectroscopy provide clear evidence for the prominent evolutionary pathways to form the catalytically active species. It is observed that the strong synergy between [PdIICl4]2−and [CuIICl4]2−is initiated by the presence of a saccharide. In the absence of a saccharide, the spectroscopic features of [PdIICl4]2−and [CuIICl4]2−in their paired solution show little change with respect to those of individual metal chloride solutions. The evolution of a highly active heterometallic PdII–Cl–CuIcomplex from paired PdCl2–CuCl2in the presence of saccharides is revealed by the transition of the FIR absorption peak of PdII–Cl. Glycolaldehyde as the simplest model compound, which is the same as the reducing end group of saccharides, is applied to determine the possible catalytic species. X-ray absorption spectroscopy (XAS) verifies that [CuIICl4]2−is reduced to [CuICl3]2−by glycolaldehyde. The HCl generated from reduced [CuIICl4]2−is also found to contribute to the hydrolysis of cellobiose, serving as another catalytically active species in paired PdCl2–CuCl2/[BMim]Cl. Paired PdCl2–CuCl2pretreated with glycolaldehyde exhibits dramatically higher activity than direct use of paired PdCl2–CuCl2in cellobiose conversion. Strikingly, the PdII–Cl–CuIcomplex is found to be substantially more active than HCl in the hydrolysis of β-1,4-glycosidic bonds as evidenced by the sustained high cellobiose conversion after neutralization of HCl with NaOH.

Atomically dispersed M-N-C (M refers to transition metals) materials represent the most promising catalyst alternatives to the precious metal Pt for the electrochemical reduction of oxygen (ORR), yet the genuine active sites in M-N-C remain elusive. Here, we develop a two-step approach to fabricate Cu-N-C single-atom catalysts with a uniform and well-defined Cu2+-N4structure that exhibits comparable activity and superior durability in comparison to Pt/C. By combining operandoX-ray absorption spectroscopy with theoretical calculations, we unambiguously identify the dynamic evolution of Cu-N4to Cu-N3and further to HO-Cu-N2under ORR working conditions, which concurrently occurs with reduction of Cu2+to Cu+and is driven by the applied potential. The increase in the Cu+/Cu2+ratio with the reduced potential indicates that the low-coordinated Cu+-N3is the real active site, which is further supported by DFT calculations showing the lower free energy in each elemental step of the ORR on Cu+-N3than on Cu2+-N4. These findings provide a new understanding of the dynamic electrochemistry on M-N-C catalysts and may guide the design of more efficient low-cost catalysts.

A new electrocatalyst of Pt single atoms dispersed into Mo2C nanocrystals in 3D porous carbon matrix derived from metal-organic frameworks pyrolysis exhibits remarkably enhanced HER activity and stability in 1 M KOH.

The catalytic hydrogenation of halonitroarenes to haloanilines is a green and sustainable process for the production of key nitrogen-containing intermediates in fine chemical industry. Chemoselective hydrogenation poses a significant challenge, which requires the rational design of the catalysts with proper hydrogenation ability for nitro group and simultaneously preventing dehalogenation of halogen group. Herein, a highly effective Rh@Al2O3@C single-atom catalyst (SAC) was developed for the hydrogenation of m-chloronitrobenzene (m-CNB) to m-chloroaniline (m-CAN), through an in-situ grafting of metal during the assembly of MIL-53 (Al), followed by confined pyrolysis. Extensive characterizations reveal an exquisite structure of the Rh@Al2O3@C, containing atomically dispersed Rh sites onto Al2O3confined by the amorphous carbon. The five-coordinated aluminum (AlV) species are essential for achieving the atomic dispersion of Rh atoms, providing the unsaturated coordinative sites for metal. Compared to the benchmark Rh/γ-Al2O3and Rh/C nanocatalysts, the Rh@Al2O3@C SAC affords an excellent turnover frequency of 2317 molm-CNB·molRh–1·h–1, the highest value to date in heterogeneous catalyst systems for the hydrogenation of m-CNB at 313 K and 20 bar H2, together with a sustained selectivity to m-CAN (~98%) during five consecutive runs. The superior catalytic performance of the Rh@Al2O3@C is attributed to a proper modulation of electronic structure of hydrogenation metal by forming SAC, together with an enhanced accessibility of acid function sites.

Transition-metal catalysts that can efficiently activate peroxide bonds have been extensively pursued for various applications including environmental remediation, chemical synthesis, and sensing. Here, we present pyridine-coordinated Co single atoms embedded in a polyaromatic macrostructure as a highly efficient peroxide-activation catalyst. The efficient catalytic production of reactive radicals through peroxymonosulfate activation was demonstrated by the rapid removal of model aqueous pollutants of environmental and public health concerns such as bisphenol A, without pH limitation and Co2+leaching. The turnover frequency of the newly synthesized Co single-atom catalyst bound to tetrapyridomacrocyclic ligands was found to be 2 to 4 orders of magnitude greater than that of benchmark homogeneous (Co2+) and nanoparticulate (Co3O4) catalysts. Experimental results and density functional theory simulation suggest that the abundant π-conjugation in the polyaromatic support and strong metal–support electronic interaction allow the catalysts to effectively adsorb and activate the peroxide precursor. We further loaded the catalysts onto a widely used poly(vinylidene fluoride) microfiltration membrane and demonstrated that the model pollutants were oxidatively removed as they simply passed through the filter, suggesting the promise of utilizing this novel catalyst for realistic applications.

Selective aerobic oxidation of alcohols under mild conditions is of great importance yet challenging, with the activation of molecular oxygen (O2) as a crucial capability of the catalysts. Herein, we demonstrate that an Al2O3-supported Pd single-atom catalyst leads to higher activity and selectivity compared to Pd nanoparticles for the oxidation of cinnamyl alcohol. The Al2O3support used in this study is rich in coordinately unsaturated Al3+sites, which are apt for binding to Pd atoms through oxygen bridges and present a distinct metal-support interaction (MSI). The suitable MSI then leads to a unique electronic characteristic of the Pd single atoms, which can be confirmed via X-ray photoelectron spectroscopy, normalized X-ray absorption near-edge structure, and diffuse reflectance Fourier transform infrared spectroscopy. Moreover, this unique electronic state is proposed to be responsible for its high catalytic activity. With the help of in-situUV-vis spectra and electron spin resonance spectra, a specific alcohol oxidation route with O2activation mechanism is then identified. Active oxygen species behaving chemically like singlet-O2are generated from the interaction of O2with Pd1/Al2O3, and then oxidize the partially dehydrogenated intermediates produced by the adsorbed allylic alcohols and Pd atoms to the desired alkenyl aldehyde. This work provides a promising path for the design and development of high-activity catalysts for aerobic oxidation reactions.

Cellulosic ethanol is one of the most important biofuels, yet its commercial production is hindered by the low-efficiency and high-cost bioconversion process. Here, we report a new chemocatalytic approach for the one-pot production of cellulosic ethanol. With a multifunctional Mo/Pt/WOxcatalyst, cellulose is directly converted to ethanol in a one-pot reaction with a yield as high as 43.2 C%. Kinetic analysis reveals that such a one-pot process involves tandem catalysis from cellulose to ethylene glycol (rapid) followed by hydrogenolysis of ethylene glycol to ethanol (slow). Characterizations show that isolated and low-coordinated MoOxbonds to metallic Pt particles on the mesoporous WOxsupport, constituting xOMo–Pt–WOxinterfacial sites, which offer high activity for C–O cleavage of ethylene glycol.

Promoters are indispensable components of Ru-based catalysts to promote N2activation in ammonia (NH3) synthesis. The rational addition and regulation of promoters play a critical role in affecting the NH3synthesis rate. In this work, we report a simple method by altering the loading sequence of Ba and Ru species to modulate the Ru-promoter interface, thus significantly boosting the NH3synthesis rate. The Ba–Ru/GC BM catalyst via the prior loading of Ba rather than Ru over graphitic carbon (GC) exhibits a high NH3synthesis rate of 18.7 mmol gcat–1h–1at 400 °C and 1 MPa, which is 2.5 times that of the Ru–Ba/GC BM catalyst via the conventional prior loading of Ru rather than Ba on GC. Our studies reveal that the prior loading of Ba benefits the high dispersion of the basic Ba promoter over an electron-withdrawing GC support, and then Ba species serve as structural promoters to stabilize Ru with small particle sizes, which exposes more active sites for N2activation. Additionally, the intimate Ba and Ru interface enables facile electron donation from Ba to Ru sites, thus accelerating N2dissociation to realize efficient NH3synthesis. This work provides a simple approach to modulating the Ru-promoter interface and maximizing promoter utilization to enhance NH3synthesis performance.

A narrow linewidth laser configuration based on distributed feedback fiber lasers (DFB-FL) with eight wavelengths in the international telecommunication union (ITU) grid is presented and realized. In this laser configuration, eight phase-shifted gratings in series are bidirectionally pumped by two 980-nm laser diodes (LDs). The final laser output with over 10-mW power for each wavelength can be obtained, and the maximum power difference within eight wavelengths is 1.2 dB. The laser configuration with multiple wavelengths and uniform power outputs can be very useful in large scaled optical fiber hydrophone fields.

A fabrication method of the multi-wavelength fiber grating (FBG) was introduced. Using the scan exposure method, the multi-wavelength FBG can be successfully manufactured through applying different tensile forces during the multiple exposures process on the same fiber. Experiment results show that the position and the overlap of different sub FBGs will greatly affect the spectrum of every sub FBG. The spectrum of each sub FBG will be affected by short wave oscillation unless the lengths and positions of all sub FBGs are fully overlapped. For hydrogen loaded fiber, the wavelength and reflectivity of the nth level FBG will increase as the (n+1)th level FBG is written. But for germanium doped photosensitive fiber, multiple exposure will increase the wavelength of previous sub FBGs while decrease the reflectivity of all sub FBGs. Through well distributing exposure intensity of every sub FBGs, a four-wavelength FBG with same sub FBG’s spectrum was fabricated on a hydrogen loaded single mode fiber.

Sepsis is a systemic inflammatory response syndrome with high morbidity and mortality mediated by infection‐caused oxidative stress. Early antioxidant intervention by removing excessively produced reactive oxygen and nitrogen species (RONS) is beneficial to the prevention and treatment of sepsis. However, traditional antioxidants have failed to improve patient outcomes due to insufficient activity and sustainability. Herein, by mimicking the electronic and structural characteristics of natural Cu‐only superoxide dismutase (SOD5), a single‐atom nanozyme (SAzyme) featuring coordinately unsaturated and atomically dispersed Cu‐N4site was synthesized for effective sepsis treatment. The de novo‐designed Cu‐SAzyme exhibits a superior SOD‐like activity to efficiently eliminate O2•−, which is the source of multiple RONS, thus blocking the free radical chain reaction and subsequent inflammatory response in the early stage of sepsis. Moreover, the Cu‐SAzyme effectively harnessed systemic inflammation and multi‐organ injuries in sepsis animal models. These findings indicate that the developed Cu‐SAzyme possesses great potential as therapeutic nanomedicines for the treatment of sepsis. A SOD‐inspired copper single‐atom nanozyme (Cu‐SAzyme) was designed and synthesized by a two‐step scaffold‐adsorption method. The Cu‐SAzyme exhibits high catalytic activity to scavenge superoxide anion, the initiator of ROS, and thus effectively prevents the disease progression in septic animals.

A SOD‐inspired copper single‐atom nanozyme (Cu‐SANzyme) was designed and synthesized by a two‐step scaffoldadsorption method. The Cu‐SANzyme exhibits high catalytic activity to scavenge superoxide anion, the initiator of ROS, and thus effectively prevents the disease progression in septic animals.

Four distributed feedback fiber lasers with dual-wavelength operations were studied experimentally in detail. The laser characteristics of these distributed feedback fiber lasers (DFB-FLs) were investigated. The operation conditions for the dual-wavelength output are analyzed and presented. Through this study, the guidance of the design and fabrication of some dual-wavelength distributed feedback fiber lasers are provided.

A distributed feedback (DFB) fiber laser with a ratio of the backward to forward output power of 1:100 was composed by a 45-mm-length asymmetrical phase-shifted fiber grating fabricated on the 50-mm erbium-doped photosensitive fiber. Forward output laser was amplified using a certain length of Nufern EDFL-980-Hp erbium-doped fiber to absorb the surplus pump power after the active phase-shifted fiber grating and get population inversion. By using OptiSystem software, the best fiber length of the EDFL to get the highest gain was simulated. In order to keep the amplified laser with the narrow line-width and low noise, a narrow-band light filter consisting of a fiber Bragg grating (FBG) with the same Bragg wavelength as the laser and an optical circulator was used to filter the amplified spontaneous emission (ASE) noise of the out-cavity erbium-doped fiber. The designed laser structure sufficiently utilized the pump power, and a DFB fiber laser with the 32.5-mW output power, 11.5-kHz line width, and −87-dB/Hz relative intensity noise (RIN) at 300 mW of 980 nm pump power was brought out.

The online fabrication of distributed feedback (DFB) fiber laser with a compact and asymmetrical cavity structure was presented. A DFB fiber laser with the total length of 1.9cm and a nearly unidirectional output which had an over 10:1 ratio for the backward to forward output was achieved. The characteristics of small dimension and unidirectional output made it suitable for sensing applications. And the fabrication procedure was easy to be carried out.

Restructuring is ubiquitous in thermocatalysis and of pivotal importance to identify the real active site, yet it is less explored in electrocatalysis. Herein, by using operandoX-ray absorption spectroscopy in conjunction with advanced electron microscopy, we reveal the restructuring of the as-synthesized Cu–N4single-atom site to the nanoparticles of ∼5 nm during the electrochemical reduction of nitrate to ammonia, a green ammonia production route upon combined with the plasma-assisted oxidation of nitrogen. The reduction of Cu2+to Cu+and Cu0and the subsequent aggregation of Cu0single atoms is found to occur concurrently with the enhancement of the NH3production rate, both of them are driven by the applied potential switching from 0.00 to −1.00 V versus RHE. The maximum production rate of ammonia reaches 4.5 mg cm–2h–1(12.5 molNH3gCu–1h–1) with a Faradaic efficiency of 84.7% at −1.00 V versus RHE, outperforming most of the other Cu catalysts reported previously. After electrolysis, the aggregated Cu nanoparticles are reversibly disintegrated into single atoms and then restored to the Cu–N4structure upon being exposed to an ambient atmosphere, which masks the potential-induced restructuring during the reaction. The synchronous changes of the Cu0percentage and the ammonia Faradaic efficiency with the applied potential suggests that the Cu nanoparticles are the genuine active sites for nitrate reduction to ammonia, which is corroborated with both the post-deposited Cu NP catalyst and density functional theory calculations.

The birefringence and optical activity of La3Ga5SiO14 crystal were studied by interferometry of polarized light. The corresponding characteristic parameters were calculated from the transmittance spectra with different orientational configuration between parallel polarisers. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical activity along the optical axis of four piezoelectric crystals Sr3TaGa3Si2O14 (STGS), Sr3NbGa3Si2O14 (SNGS), Ca3TaGa3Si2O14 (CTGS) and Ca3NbGa3Si2O14 (CNGS) with ordered langasite structure were studied via a convenient method. All the crystals investigated show unusually large values of the specific rotation. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)