New insight into the design of highly dispersed Pt supported CeO_(2)-TiO_(2) catalysts with superior activity for VOCs low-temperature removal

A series of CeO_(2)-TiO_(2)mixed oxides supports with various Ce/Ti molar ratio were synthesized by modified coprecipitation method. The corresponding Pt loaded(0.5 wt% Pt) catalysts were prepared by electronless deposition method and evaluated for the deep oxidation of n-hexane as a model VOCs. The results show that the CeO_(2)and TiOxnanoparticles can highly disperse into each other and form Ce_(2)Ti_(2)O_(7)solid solution with appropriate Ce/Ti molar ratio, which significantly improves their redox ability by enhancing the interaction between CeO_(2)and TiO_(x). The dispersibility of Pt species can also be adjusted by altering the Ce/Ti molar ratio, and Pt/CeTi-2/1 catalyst with Ce/Ti molar ratio of 2:1 exhibits the best Pt dispersibility that Pt species mainly exist as Pt single atoms. The high dispersion of Pt species in the Pt/CeO_(2)-TiO_(2)catalysts would promote the catalytic activity of VOCs oxidation with low T90% values(1000 ppm, GHSV = 15,000 h^(-1)), such as for n-hexane degradation with T90% of 139℃. The characterizations reveal that the superior activity is mainly related to possessing the more Pt2+species,adsorbed oxygen species and higher low-temperature reducibility owing to the strong interaction between highly dispersed Pt species and CeO_(2)-TiO_(2)as well as the promoted migration of lattice oxygen by the formation of more Ce_(2)Ti_(2)O_(7)species. Furthermore, the Pt/CeTi-2/1 catalyst also exhibits excellent stability for chlorinated and other non-chlorinated VOCs oxidation, making it very promising for real application under various operating conditions.

A Fe-N-C catalyst with highly dispersed iron in carbon for oxygen reduction reaction and its application in direct methanol fuel cells

Exploring non‐precious metal catalysts for the oxygen reduction reaction （ORR） is essential for fuel cells and metal–air batteries. Herein, we report a Fe‐N‐C catalyst possessing a high specific surface area （1501 m2/g） and uniformly dispersed iron within a carbon matrix prepared via a two‐step pyrolysis process. The Fe‐N‐C catalyst exhibits excellent ORR activity in 0.1 mol/L NaOH electrolyte （onset potential, Eo=1.08 V and half wave potential, E1/2=0.88 V vs. reversible hydrogen electrode） and 0.1 mol/L HClO4 electrolyte （Eo=0.85 V and E1/2=0.75 V vs. reversible hydrogen electrode）. The direct methanol fuel cells employing Fe‐N‐C as the cathodic catalyst displayed promising per‐formance with a maximum power density of 33 mW/cm2 in alkaline media and 47 mW/cm2 in acidic media. The detailed investigation on the composition–structure–performance relationship by X‐ray diffraction, X‐ray photoelectron spectroscopy and Mo-ssbauer spectroscopy suggests that Fe‐N4, together with graphitic‐N and pyridinic‐N are the active ORR components. The promising direct methanol fuel cell performance displayed by the Fe‐N‐C catalyst is related to the intrinsic high catalytic activity, and critically for this application, to the high methanol tolerance.

Ru/FeO_x catalyst performance design: Highly dispersed Ru species for selective carbon dioxide hydrogenation

A series of Ru/FeOx catalysts were synthesized for the selective hydrogenation of CO2to CO.Detailed characterizations of the catalysts through X‐ray diffraction,X‐ray photoelectron spectroscopy,transmission electron microscopy,and temperature‐programmed techniques were performed to directly monitor the surface chemical properties and the catalytic performance to elucidate the reaction mechanism.Highly dispersed Ru species were observed on the surface of FeOx regardless of the initial Ru loading.Varying the Ru loading resulted in changes to the Ru coverage over the FeOx surface,which had a significant impact on the interaction between Ru and adsorbed H,and concomitantly,the H2activation capacity via the ability for H2dissociation.FeOx having0.01%of Ru loading exhibited100%selectivity toward CO resulting from the very strong interaction between Ru and adsorbed H,which limits the desorption of the activated H species and hinders over‐reduction of CO to CH4.Further increasing the Ru loading of the catalysts to above0.01%resulted in the adsorbed H to be easily dissociated,as a result of a weaker interaction with Ru,which allowed excessive CO reduction to produce CH4.Understanding how to selectively design the catalyst by tuning the initial loading of the active phase has broader implications on the design of supported metal catalysts toward preparing liquid fuels from CO2.?2018,Dalian Institute of Chemical Physics,Chinese Academy of Sciences toward preparing liquid fuels from CO2.?2018,Dalian Institute of Chemical Physics,Chinese Academy of Sciences.Published by Elsevier B.V.All rights reserved.

Highly Dispersed Pt Species with Excellent Stability and Catalytic Performance by Reducing a Perovskite-Type Oxide Precursor for CO Oxidation

A new scheme for the preparation of highly dispersed precious metal catalysts is proposed in this work. Samples of LaCol-xPtxO3/SiO2 （x = 0.03, 0.05, 0.07, 0.09, and 0.10） were prepared through a simple method of citrate acid complexa-tion combined with impregnation. In a nanocrystallite of LaCOl-xPtxO3, ions of lanthanum, cobalt, and platinum are evenly mixed at the atomic level and confined within the nanocrystallite. In the reduction process, platinum ions were reduced and migrated onto the surface of the nanocrystallite, and the platinum should be highly dispersed owing to the even mixing of the platinum ions in the precursor. When x = 0.05 or lower, the highest dispersion of Pt could be achieved. The highly dispersed Pt is stable, because of the strong interaction between Pt atoms and the support. The catalysts were characterized by BET surface area, temperature-programmed reduction, X-ray diffraction, transmission electron microscopy, CO temperature-programmed desorption, and turnover frequency. Compared with general precious metal Pt catalysts, the LaCo0.95Pt0.05O3/ SiO2 catalyst exhibited better activity for CO oxidation, and it maintained stability at a high temperature of 400 ℃ for 250 h with complete CO conversion.

Highly dispersed Ru nanospecies on N-doped carbon/MXene composite for highly efficient alkaline hydrogen evolution

Hydrogen has emerged as a promising environmentally friendly energy source. The development of lowcost, highly active, stable, and easily synthesized catalysts for hydrogen evolution reactions(HER) remains a significant challenge. This study explored the synthesis of nitrogen-doped MXene-based composite catalysts for enhanced HER performance. By thermally decomposing RuCl_(3) coordinated with melamine and formaldehyde resin, we successfully introduced nitrogen-doped carbon(N–C) with highly dispersed ruthenium(Ru) onto the MXene surface. The calcination temperature played a crucial role in controlling the size of Ru nanoparticles(Ru NPs) and the proportion of Ru single-atom(Ru SA), thereby facilitating the synergistic enhancement of HER performance by Ru NPs and Ru SA. The resulting catalyst prepared with a calcination temperature of 600℃, Ti_(3)C_(2)T_x-N/C-Ru-600(TNCR-600), exhibited exceptional HER activity(η10= 17 m V) and stability(160 h) under alkaline conditions. This work presented a simple and effective strategy for synthesizing composite catalysts, offering new insights into the design and regulation of high-performance Ru-based catalysts for hydrogen production.

Dehydrogenation activities of highly dispersed transition metal oxides on NaY zeolite

Highly dispersed α-Fe_2O_3/NaY,NiO/NaY,and CuO/NaY catalyst systems were pre- pared by impregnation method.Dispersion thresholds of the transition metal oxides on NaY' zeolite were determined by XRD phase analysis.The dispersion capacities of the transition metal oxides on NaY zeolite are much lower than that estimated on the basis of a closed packed monolayer in the micro pores.The catalytic activity and selectivity of the highly dispersed oxide catalyst systems for ethylben- zene and cyclohexane dehydrogenation reactions were reported.

The highly dispersed Co-based nanoparticles encapsulated into porous N-doping carbon polyhedral with the low content of Ru modification as a promising cathode catalyst for long-life Li-O_(2)batteries

Lithium(Li)-O_(2)batteries have triggered worldwide interest due to their ultrahigh theoretical energy density.However,it is a long shot for the grand-scale applications of Li-O_(2)battery at current stage owing to its significant polarization,inferior cycling life,and irreversible decomposition of Li2O_(2).Herein,a facile way of preparing the highly dispersed Co-based nanoparticles encapsulated into porous N-doping carbon polyhedral with the low content of Ru modification(LRu@HDCo-NC)is explored through the pyrolysis of Co/Zn based zeolitic imidazole frameworks(ZIFs)containing Ru-based ligands.Even with the very small amount of Ru introduction(1.8%),LRu@HDCo-NC still exhibits the superior oxygen evolution reaction/oxygen reduction reaction(OER/ORR)performance and also inhibits side reactions in Li-O_(2)battery because of the abundant pores,plentiful surface N heteroatoms,and highly dispersed metal-based sites which are induced by the volatilization of Zn,and conductive/stable carbon skeleton derived from ZIFs.When applied in Li-O_(2)batteries,LRu@HDCo-NC cathode delivers a high discharge capacity of 15,973 mAh·g^(-1)at 200 mA·g^(-1),good capacity retention at higher rate(12,362 mAh·g^(-1)at 500 mA·g^(-1))and outstanding stability for>300 cycles with low voltage polarization of<2.3 V under a cut-off capacity of 1,000 mAh·g^(-1)at 500 mA·g^(-1).More critically,a series of ex situ and in situ characterization technologies disclose that the LRu@HDCo-NC cathodes can effectively promote the reversible reactions in Li-O_(2)batteries.

A highly stable and active mesoporous ruthenium catalyst for ammonia synthesis prepared by a RuCl_3/SiO_2-templated approach

Molecular nitrogen is relatively inert and the activation of its triple bond is full of challenges and of significance.Hence,searching for an efficiently heterogeneous catalyst with high stability and dispersion is one of the important targets of chemical technology.Here,we report a Ba‐K/Ru‐MC catalyst with Ru particle size of 1.5–2.5 nm semi‐embedded in a mesoporous C matrix and with dual promoters of Ba and K that exhibits a higher activity than the supported Ba‐Ru‐K/MC catalyst,although both have similar metal particle sizes for ammonia synthesis.Further,the Ba‐K/Ru‐MC catalyst is more active than commercial fused Fe catalysts and supported Ru catalysts.Characterization techniques such as high‐resolution transmission electron microscopy,N2 physisorption,CO chemisorption,and temperature‐programmed reduction suggest that the Ru nanoparticles have strong interactions with the C matrix in Ba‐K/Ru‐MC,which may facilitate electron transport better than supported nanoparticles.

CNT modified by mesoporous carbon anchored by Ni nanoparticles for CO_(2) electrochemical reduction

The design of novel catalysts for efficient electroreduction of CO_(2) into valueadded chemicals is a promising approach to alleviate the energy crisis.Herein,we successfully modify the carbon nanotube by a layer of mesoporous carbon shell anchored by nickel(Ni)nanoparticles.Ni species effectively enable carbon deposition derived from pyrolysis of surfactant 1-hexadecyl trimethyl ammonium bromide to form a mesoporous carbon shell.At the same time,Ni nanoparticles can be embedded in the mesoporous carbon shell due to the confinement effect.Owing to the dispersive Ni nanoparticles and N-doping active sites of mesoporous carbon,the as-prepared electrocatalyst exhibits exciting catalytic performance for the selective reduction of CO_(2) to carbon monoxide(CO)with a maximum Faradaic efficiency of 98%at a moderate overpotential of−0.81 V(vs.reversible hydrogen electrode)and a high partial current density of 60 mA cm^(−2) in H-cell with an aqueous electrolyte.

Platinum catalysts supported on Nafion functionalized carbon black for fuel cell application

We report a high performance supported Pt catalyst, in which a perfluorosulfonic acid （Nation） functionalized carbon black is used as support. The catalyst is characterized by infrared spectroscopy （IR）, transmission electron microscopy （TEM） and X-ray diffraction （XRD）. The TEM image shows that the active Pt component is in nanoparticles and highly dispersed on the carbon black with an average particle size of 1.9 nm. The catalyst shows improved activity towards the methanol anodic oxidation and oxygen reduction reaction （ORR）, resulting from the high dispersion of active Pt component. It leads to increases in electrochemically accessible surface areas and ion channels, as well as easier charge- transfer at polymer/electrolyte interfaces. The high platinum utilization and high performance of Pt/Nafion-C catalyst make it a promising electrocatalyst for fuel cell application.

Enhanced performance for propane dehydrogenation through Pt clusters alloying with copper in zeolite

Metal alloys have been widely applied for heterogeneous catalysis,especially alkane dehydrogenation.However,the catalysts always suffer from sintering and coke deposition due to the rigorous reaction conditions.Herein,we described an original approach to prepare a catalyst where highly dispersed Pt clusters alloying with copper were encapsulated in silicalite-1(S-1)zeolite for propane dehydrogenation(PDH).The introduction of Cu species significantly enhances the catalytic activity and prolongs the lifetime of the catalyst.0.1Pt0.4CuK@S-1 exhibits a propane conversion of 24.8%with 98.2%selectivity of propene,and the specific activity of propylene formation is up to 32 mol·gPt^(−1)·h^(−1)at 500℃.No obvious deactivation is observed even after 73 h on stream,affording an extremely low deactivation constant of 0.00032 h^(−1).The excellent activity and stability are ascribed to the confinement of zeolites and the stabilization of Cu species for Pt clusters.

Facile synthesis of C_(3)N_(4)-supported metal catalysts for efficient CO_(2) photoreduction

Facile synthesis of photocatalysts with highly dispersed metal centers is a high-priority target yet still a significant challenge.In this work,a series of Co-C_(3)N_(4) photocatalysts with different Co contents atomically dispersed on g-CaN4 have been prepared via one-step thermal treatment of cobalt-based metal-organic frameworks(MOFs)and urea in the air.Thanks to the highly dispersed and rich exposed Co sites,as well as good charge separation efficiency and abundant mesopores,the optimal 25-Co-C_(3)N_(4),in the absence of noble metal catalysts/sensitizers,exhibits excellent performance for photocatalytic C0_(2) reduction to CO under visible.light irradiation,with a high CO evolution rate of 394.4μmol·g^(-1)·h^(-1),over 80 times higher than that of pure g-C_(3)N_(4)(4.9μmol·g^(-1)·h^(-1)).In:addition,by this facile synthesis strategy,the atomically dispersed Fe and Mn anchoring on g-C_(3)N_(4)(Fe-C_(3)N_(4) and Mn-C_(3)N_(4))have been also obtained,indicating the reliability and universality of this strategy in synthesizing photocatalysts with highly dispersed metal centers.This work paves a new way to develop cost-effective photocatalysts for photocatalytic C0_(2) reduction.

Synthesis of Ag-SiO_2 composite nanospheres and their catalytic activity

A simple,mild,and time-saving method is employed to synthesize Ag-SiO2 composite nanospheres with Ag nanoparticles uniformly distributed on the surface of SiO2 nanoparticles.The chemical elements and the morphology of Ag-SiO2 composite nanospheres were analyzed with transmission electron microscopy(TEM),X-ray power diffraction(XRD),and X-ray photoelectron spectroscopy(XPS).On the surface of Ag-SiO2 composite nanospheres,silane coupling agent(KH-550)is introduced as an intermediary to connect the surfaces of SiO2 nanospheres and Ag nanoparticles,which is also helpful for avoiding the aggregation of Ag nanoparticles.It is found that Ag-SiO2 composite nanospheres have very good catalytic properties for the reduction of organic dyes,which may have potential application in wastewater treatment.

Kinetically rate-determining step modulation by metal-support interactions for CO oxidation on Pt/CeO_(2)

Rational design and performance promotion are eternal topics and ultimate goals in catalyst preparation.In contrast,trial–and–error is still the common method people take.Therefore,it is important to develop methods to intrinsically enhance the performance of catalysts.The most effective solutions are the one from a kinetic perspective based on clear knowledge of the reaction mechanism.This paper describes rate-determining step cognition and modulation to promote CO oxidation on highly dispersed Pt on CeO_(2).The different degrees of metal–support interactions due to variation of hydroxyl density of support could alter the structure of active species and the ability of oxygen activation apparently,further shift the rate-determining step from oxygen activation to oxygen reverse spillover kinetically.The transformation of rate-determining step could enhance the intrinsic activity significantly,and decrease the T_(50) approximately 140℃.The findings of this research exemplify the universal and effective method of performance elevation by rate-determining step modulation,which is promising for application in different systems.

Characterization and catalytic properties of mesoporous CuO/SBA-16 prepared by different impregnation methods

CuO/SBA-16 catalysts were prepared by two different routes–the conventional impregnation method and the modified impregnation method with pH adjustment.These catalysts were characterized by X-ray diffraction(XRD),atomic absorption spectrometry(AAS),N2 physisorption and hydrogen temperature programmed reduction(H2-TPR)measurements which reveal that the cubic cagelike(Im3m)pore structure of the parent SBA-16 molecule sieves was well maintained throughout the synthesis.After introduction of Cu,a different CuO dispersion exists on these catalysts.The CuO/SBA-16 prepared by modified impregnation method has a single highly dispersed CuO which is considered as a highly efficient species for hydroxylation of phenol withH2O2.CuO/SBA-16 prepared by the conventional impregnation method shows the presence of bulk CuO species which is undesirable for this reaction.

A review of friction stir welding of steels： Tool, material flow, microstructure, and properties

Considerable progress has been achieved in friction stir welding （FSW） of steels in every aspect of tool fab- rication, microstructure control and properties evaluation in the past two decades. With the development of reliable welding tools and precise control systems, FSW of steels has reached a new level of technical maturity. High-quality, long welds can be produced in many engineering steels. Compared to traditional fusion welding, FSW exhibits unique advantages producing joints with better properties. As a result of active control of the welding temperature and/or cooling rate, FSW has the capability of fabricating steel joints with excellent toughness and strength. For example, unfavorable phase transformations that usu- ally occur during traditional welding can be avoided and favorable phase fractions in advanced steels can be maintained in the weld zone thus avoiding the typical property degradations associated with fusion welding. If phase transformations do occur during FSW of thick steels, optimization of microstructure and properties can be attained by controlling the heat input and post-weld cooling rate.

Combination of ionic liquid dispersive liquid-phase microextraction and high performance liquid chromatography for the determination of triazine herbicides in water samples

A temperature-controlled ionic liquid dispersive liquid-phase microextraction in combination with high performance liquid chromatography was developed for the enrichment and determination of triazine herbicides such as cyanazine,simazine,and atrazine in water samples.1-Octyl-3-methylimidazolium hexafluorophosphate（[C8MIM][PF6]） was selected as the extraction solvent.Several experimental parameters were optimized.Under the optimal conditions,the linear range for cyanazine was in the concentration range of 0.5–80 mg/L and the linear range for simazine and atrazine was in the range of1.0–100 mg/L.The limit of detection（LOD,S/N = 3） was in the ranges of 0.05–0.06 mg/L,and the intra day and inter day precision（RSDs,n = 6） was in the ranges of 3.2%–6.6% and 4.8%–8.9%,respectively.Four real water samples were analyzed with the developed method,and the experimental results showed that the spiked recoveries were satisfactory.All these exhibited that the developed method was a valuable tool for monitoring such pollutants.

High Differential Group Index of Dispersion Compensating Fibers for OCDMA Encoder/Decoder

We report the LPG pair device that can be used as a pulse duplicator or an OCDMA encoder/decoder. Due to the ring core region of dispersion compensating fiber (DCF), we can shorten the device length by a third and obtain surrounding insensitive LPG devices.