Homoleptic alkynyl-protected Ag_(32 )nanocluster with atomic precision: Probing the ligand effect toward CO_(2) electroreduction and 4-nitrophenol reduction

We report a superatomic homoleptic alkynyl-protected Ag_(32)L_(24)(L=3,5-bis(trifluoromethylbenzene)acetylide,Ag_(32) for short)nanocluster with atomic precision,which possesses eight free electrons.Ag_(32) is formed by an Ag17 core with C3 symmetry and the remaining 15 Ag atoms bond to each other and coordinate with the 24 surface ligands.When applied as electrocatalyst for CO_(2) reduction reaction(CO_(2)RR),Ag_(32) exhibited the highest Faradaic efficiency(FE)of CO up to 96.44%at−0.8 V with hydrogen evolution being significantly suppressed in a wide potential range,meanwhile it has a reaction rate constant of 0.242 min−1 at room temperature and an activation energy of 45.21 kJ·mol−1 in catalyzing the reduction of 4-nitrophenol,both markedly superior than the thiolate and phosphine ligand co-protected Ag_(32) nanocluster.Such strong ligand effect was further understood by density functional theory(DFT)calculations,as it revealed that,one single ligand stripping off from the intact cluster can create the undercoordinated Ag atom as the catalytically active site for both clusters,but alkynyl-protected Ag_(32) nanocluster possesses a smaller energy barrier for forming the key*COOH intermediate in CO_(2)RR,and favors the adsorption of 4-nitrophenol.This study not only discovers a new member of homoleptic alkynyl-protected Ag nanocluster,but also highlights the great potentials of employing alkynyl-protected Ag nanoclusters as bifunctional catalysts toward various reactions.

Pre-reduction of WO_(3)-Co_(3)O_(4)by H_(2)-C_(2)H_4 in a fluidized bed

In order to avoid the formation ofηphase(W_(6)Co_(6)C or W_(3)Co_(3)C)that adversely affects the sintering process and its products in the preparation process of ultra-fine WC-Co powder,a technical route of prereduction of WO_(3)-Co_(3)O_(4)to WO_(2)-Co and then deep reduction carbonization to WC-Co powder has been proposed.This study mainly investigates the influence of gas partial pressure on the pre-reduction process of WO_(3)-Co_(3)O_(4)under a mixed atmosphere of H_(2)-C_(2)H_(4)-Ar at 600℃and establishes the kinetic equations of pre-reduction and carbon evolution.The results indicate that increasing the partial pressure of hydrogen is conducive to the rapid and complete conversion of WO_(3) to WO_(2).High carbon content can be generated by the deposition of C_(2)H_(4),and it hinders the diffusion of the reducing gas;WO_(3)still cannot be completely reduced to WO_(2)as the partial pressure of C_(2)H_(4) increases to 60%.For the carbon evolution of C_(2)H_(4),the carbon amount is positively related to the H_(2)partial pressure,but it shows the highest amount and evolution rate when the ethylene partial pressure is 20%.Based on the reduction rate curves of WO_(3) and carbon evolution rate curves of C_(2)H_(4),the rate equations of pre-reduction and carbon evolution of WO_(3)-Co_(3)O_(4)system at 600℃are established.The pre-reduction reaction belongs to the first-order reaction,and its equation is expressed as follows:r=-(dw_(WO_(3)))/dt=(9±0.15)×10^(-2)×P_(H_(2))^(0.44)P_(C_(2)H_(4))&(0.57)The carbon deposition rate equation of C_(2)H_(4) can be expressed as follows:r=-(dc_C)/dt=r_f-r_b≌7.35×10^(-2)×P_(C_(2)H_(4))^(0.31)

Highly selective photocatalytic reduction of CO_(2) to CH_(4) on electron-rich Fe species cocatalyst under visible light irradiation

Efficient photocatalytic reduction of CO_(2) to high-calorific-value CH4,an ideal target product,is a blueprint for C_(1)industry relevance and carbon neutrality,but it also faces great challenges.Herein,we demonstrate unprecedented hybrid SiC photocatalysts modified by Fe-based cocatalyst,which are prepared via a facile impregnation-reduction method,featuring an optimized local electronic structure.It exhibits a superior photocatalytic carbon-based products yield of 30.0μmol g^(−1) h^(−1) and achieves a record CH_(4) selectivity of up to 94.3%,which highlights the effectiveness of electron-rich Fe cocatalyst for boosting photocatalytic performance and selectivity.Specifically,the synergistic effects of directional migration of photogenerated electrons and strongπ-back bonding on low-valence Fe effectively strengthen the adsorption and activation of reactants and intermediates in the CO_(2)→CH_(4) pathway.This study inspires an effective strategy for enhancing the multielectron reduction capacity of semiconductor photocatalysts with low-cost Fe instead of noble metals as cocatalysts.

Tuning Structural and Electronic Configuration of FeN_(4) via External S for Enhanced Oxygen Reduction Reaction

The Fe-N-C material represents an attractive oxygen reduction reaction electrocatalyst,and the FeN_(4)moiety has been identified as a very competitive catalytic active site.Fine tuning of the coordination structure of FeN_(4)has an essential impact on the catalytic performance.Herein,we construct a sulfur-modified Fe-N-C catalyst with controllable local coordination environment,where the Fe is coordinated with four in-plane N and an axial external S.The external S atom affects not only the electron distribution but also the spin state of Fe in the FeN_(4)active site.The appearance of higher valence states and spin states for Fe demonstrates the increase in unpaired electrons.With the above characteristics,the adsorption and desorption of the reactants at FeN_(4)active sites are optimized,thus promoting the oxygen reduction reaction activity.This work explores the key point in electronic configuration and coordination environment tuning of FeN_(4)through S doping and provides new insight into the construction of M-N-C-based oxygen reduction reaction catalysts.

Healing the structural defects of spinel MnFe_(2)O_(4) to enhance the electrocatalytic activity for oxygen reduction reaction

Spinel metal oxides containing Mn,Co,or Fe(AB_(2)O_(4),A/B=Mn/Fe/Co)are one of the most promising nonPt electrocatalysts for oxygen reduction reaction(ORR)in alkaline conditions.However,the low conductivity of metal oxides and the poor intrinsic activities of transition metal sites lead to unsatisfactory ORR performance.In this study,eutectic molten salt(EMS)treatment is employed to reconstruct the atomic arrangement of MnFe_(2)O_(4)electrocatalyst as a prototype for enhancing ORR performance.Comprehensive analyses by using XAFS,soft XAS,XPS,and electrochemical methods reveal that the EMS treatment reduces the oxygen vacancies and spinel inverse in MnFe_(2)O_(4)effectively,which improves the electric conductivity and increases the population of more catalytically active Mn^(2+)sites with tetrahedral coordination.Moreover,the enhanced Mn-O interaction after EMS treatment is conducive to the adsorption and activation of O_(2),which promotes the first electron transfer step(generally considered as the ratedetermining step)of the ORR process.As a result,the EMS treated MnFe_(2)O_(4)catalyst delivers a positive shift of 40 mV in the ORR half-wave potential and a two-fold enhanced mass/specific activity.This work provides a convenient approach to manipulate the atomic architecture and local electronic structure of spinel oxides as ORR electrocatalysts and a comprehensive understanding of the structureperformance relationship from the molecular/atomic scale.

Research Progress in Photocatalytic CO_(2) Reduction with ZnIn_(2)S_(4)-Based Nanomaterials(Ⅰ)

Zinc indium sulfide(ZnIn_(2)S_(4),ZIS),a novel photocatalyst with layered nanostructure,has drawn significant attention in the field of photocatalytic CO_(2) reduction in recent years due to various advantages,including non-toxicity,structural stability,easy availability,and suitable band gap.We introduced the types of ZISbased nanomaterials and their action mechanism in photocatalytic CO_(2) reduction.Moreover,we put forward prospects in the future development directions of ZIS-based nanomaterials for photocatalytic CO_(2) reduction.

Research Progress in Photocatalytic CO_(2)Reduction with ZnIn_(2)S_(4)-Based Nanomaterials(Ⅱ)

Zinc indium sulfide(ZnIn_(2)S_(4),ZIS),a novel photocatalyst with layered nanostructure,has drawn significant attention in the field of photocatalytic CO_(2)reduction in recent years due to various advantages,including non-toxicity,structural stability,easy availability,and suitable band gap.We introduce the types of ZIS-based nanomaterials and their action mechanism in photocatalytic CO_(2)reduction.Moreover,we put forward prospects in the future development directions of ZIS-based nanomaterials for photocatalytic CO_(2)reduction.

Facile g-ray irradiation synthesis of Pt/GA nanocomposite for catalytic reduction of 4-nitrophenol

Up to now,facile and pollution-free routes for catalyst preparation are in high demand.In this study,a green and cost-effective strategy was successfully developed to construct platinum/graphene aerogel(Pt/GA)nanocomposites by the co-reduction of graphene oxides(GO)and chloroplatinic acid(H_(2)PtCl6$6H_(2)O)with the assists of g-ray irradiation in the absence of any other reductants.Characterization studies indicated that the energy of g-ray irradiation and the hole scavenger isopropanol(IPA)played a vital role in forming small Pt nanoparticles with uniform size of~3 nm on the surface of graphene aerogel(GA).Furthermore,Pt/GA synthesized with a mass ratio of 2:1(Pt/GA-2)exhibited a lowest activation energy value and outstanding catalytic properties for the reduction of 4-nitrophenol(4-NP).The excellent catalytic and cycling performance suggest that Pt/GA-2 catalyst has a promising prospect for the reduction of nitroaromatic compounds in wastewater treatment and other industrial applications.

Versatile bifunctional nitrogen-doped porous carbon derived from biomass in catalytic reduction of 4-nitrophenol and oxidation of styrene

The scarcity and weak durability of metal,especially precious metal catalysts are big obstacles for their large-scale application in many reactions.The state-of-the-art of the catalytic science prefers such type of catalysts,which can replace metal-based catalysts to alleviate energy and environmental crises and exhibit catalytic performance comparable to or even exceeding these metal catalysts.Herein,we report that N-doped porous carbon(NKC)derived from cheap and abundant radish can be employed as versatile and efficient bifunctional catalysts in both the catalytic reduction of 4-nitrophenol(NRR)and oxidation of styrene(SOR).The series of NKC catalysts were prepared with a simple and facile one-pot strategy by coupling the N-doping,carbonization and KOH activation processes.These catalysts show hierarchical porosity,with the specific surface area,total pore volume and N-doping content ranging from 918.9-3062.7 m^2 g^-1,1.01-2.04 cm^3 g^-1 and 1.29-15.3 at%,respectively.Interestingly,our finding suggests that the catalytic performance is not directly related to these parameters but correlates positively with the content of graphitic N dopants,which is the dominant contributor for impelling both the NRR and SOR.Another intriguing finding is that for both reactions,the optimal catalyst was found to be the NKC-3-800 which possesses the highest graphitic N content of 3.13 at%.In addition,to gain insight into the catalytic behavior,analyses of kinetics and thermodynamics were performed,and the catalytic mechanisms were postulated.This work paves the way for the construction of biomass-derived N-doped carbon catalysts for bi-or even multi-functional applications in various organic reactions.

Experimental design for optimization of 4-nitrophenol reduction by green synthesized CeO2/g-C3N4/Ag catalyst using response surface methodology

In this study,the enhancement of catalytic activity of ceria when modified with co-catalysts such as graphitic carbon nitride and silver was establishe d.The material was synthe sized using phytogenic combustion method,a green alternative to the traditional preparative routes.The catalyst was characterized using XRD,FTIR,SEM,EDX,XPS and TEM techniques.The synergistic effect of the composite CeO2/g-C3 N4/Ag was tested for catalytic reduction of 4-nitrophenol in the prese nce of sodium borohydride.The reaction was carried out at room tempe rature without any light source or exte rnal stirring.The individual and combined effects of four parameters,viz.,concentration of 4-NP,amount of catalyst,amount of NaBH4 and time for the reduction of reduction 4-NP were investigated using Box-Behnken design of response surface methodology(RSM).This statistical model was used to optimize the reaction conditions for maximum reduction of 4-NP.The optimum conditions for the reduction reaction are found to be 0.01 mmol/L 4-NP,15 mg catalyst,20 mg NaBH4 and 13.7 min time interval.

Kinetically controlled synthesis of atomically precise Ag nanoclusters for the catalytic reduction of 4-nitrophenol

Synthesizing atomically precise Ag nanoclusters(NCs),which is essential for the general development of NCs,is quite challenging.In this study,we report the synthesis of high-purity atomically precise Ag NCs via a kinetically controlled strategy.The Ag NCs were prepared using a mild reducing agent via a one-pot method.The as-prepared Ag NCs were confirmed to be Ag_(49)(D-pen)_(24)(D-pen:D-penicillamine)on the basis of their matrix-assisted laser desorption ionization time-of-flight mass spectrometric and thermogravimetric characteristics.The interfacial structures of the Ag NCs were illustrated by proton nuclear magnetic resonance and Fourier-transform infrared spectroscopy.The Ag NCs were supported on activated carbon(AC)to form Ag NCs/AC,which displayed excellent activity for the catalytic reduction of 4-nitrophenol with a kinetic reaction rate constant k of 0.21 min^(-1).Such a high k value indicates that the composite could outperform several previously reported catalysts.Moreover,the catalytic activity of Ag NCs/AC remained nearly constant after six times of recycle,which suggests its excellent stability.

Reduction of 4-nitrophenol catalyzed by nitroreductase

The reduction of 4-nitrophenol catalyzed by nitroreductase in the presence of NADH was investigated in this paper. 4-Amino- phenol and 4-hydroxylamino-phenol were found in the reductive products. The relationship between reaction time and the reductive ratio were studied. The similar reducing ratios of 4-nitrophenol were obtained under aerobic and anaerobic conditions. The results indicated that an oxygen-insensitive reaction was proceeded in the reduction of 4-nitrophenol and nitroreductase was an oxygeninsensitive enzyme. The reductive products of 4-nitrophenol were determined by HPLC and MS.

CO oxidation and 4-nitrophenol reduction over ceria-promoted platinum nanoparticles impregnated with ZSM-5 zeolite

Active new ceria-promoted platinum supported on ZSM-5 catalysts were prepared and characterized by X-ray diffraction(XRD),Fourier transform infrared spectra(FTIR),transform electron microscopy(TEM),temperature programmed desorption(TPD),and FTIR of CO adsorption.The samples were prepared by the incipient wetness impregnation method and calcined at 500℃.The XRD patterns and FTIR spectra prove that the zeolite framework is kept unaltered after metal loadings.TEM images prove the presence of Pt nanoparticles with particle size starting from 14 to 27 nm.The FTIR data suggest the formation of Pt-O-Ce linkage.In-situ FTIR of CO adsorption over reduced samples proves the presence of Pt~0 only,and no Pt^(n+)-CO species are detected.The prepared catalysts were tested in both oxidation reaction(CO oxidation) in the gas phase and in reduction reaction(4-nitrophenol reduction) in the aqueous medium.Firstly,CO oxidation by O_(2) results in the formation of a CO_(2) peak at 2347 cm^(-1) as the only CO oxidation product in the studied frequency range.The intensity of the CO_(2) peak increases after the addition of Ce,and it is 4 times higher in Pt_(1) Ce_(0.5)ZSM-5 than that in the Ce-free sample.According to the FTIR data and previous reports,the increase in the catalytic activity may be due to the formation of Pt-O-Ce linkage.Secondly,Ce-promoted Pt_(1) ZSM5 also exhibits enhanced catalytic activity towards the reduction of 4-nitrophenol to 4-aminophenol by NaBH_(4) in the aqueous medium.The first-order rate constant of the reduction increases ≈13 times after incorporating equal ratios of Pt and Ce(Pt_(1) Ce_(1)ZSM-5),and the activation energy(E_(a)) decreases to 40% of that in the reaction over Pt_(1) ZSM-5.

Deposition of Pd on Co(OH)_(2) nanoplates in stabilizer-free aqueous phase for catalytic reduction of 4-nitrophenol

Palladium-supported cobalt hydroxide(Co(OH)_(2)-Pd) nanoplates were fabricated in an aqueous solution and employed as a catalyst for the reduction of 4-nitrophenol.For the preparation of Co(OH)2-Pd,Pd nanoparticles were anchored on the Co(OH)_(2) nanoplates after the reduction of Na;PdCl;by ascorbic acid in the absence of a stabilizer at room temperature.The observations under transmission and scanning electron microscopy reveal that Pd nanoparticles with a size of 2-5 nm are uniformly dispersed on the surface of the Co(OH)_(2) nanoplates.In catalytic test,the conversion of 4-nitrophenol to 4-aminophenol is completed within 6 min in the presence of Co(OH)_(2)-Pd(1000) nanoplates with2.18 at.% Pd,and the corresponding kinetic constant is 0.0089 s;in the first test.The catalyst retains relatively high activity after several cycles.The results demonstrate that the Co(OH)_(2)-Pd(1000) nanoplates exhibit high catalytic activity toward the reduction of 4-nitrophenol in the presence of NaBH;.

Co_3O_4 nanoparticles assembled on polypyrrole/graphene oxide for electrochemical reduction of oxygen in alkaline media

The development of highly efficient catalysts for cathodes remains an important objective of fuel cell research. Here, we report Co3O4 nanoparticles assembled on a polypyrrole/graphene oxide electrocatalyst （Co3O4/Ppy/GO） as an efficient catalyst for the oxygen reduction reaction （ORR） in alkaline media. The catalyst was prepared via the hydrothermal reaction of Co2＋ ions with Ppy-modified GO. The GO, Ppy/GO, and Co3O4/Ppy/GO were characterized using scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The incorporation of Ppy into GO nanosheets resulted in the formation of a nitrogen-modified GO po-rous structure, which acted as an efficient electron-transport network for the ORR. With further anchoring of Co3O4 on Ppy/GO, the as-prepared Co3O4/Ppy/GO exhibited excellent ORR activity and followed a four-electron route mechanism for the ORR in alkaline solution. An onset potential of -0.10 V vs. a saturated calomel electrode and a diffusion limiting current density of 2.30 mA/cm^2 were achieved for the Co3O4/Ppy/GO catalyst heated at 800 ℃; these values are comparable to those for noble-metal-based Pt/C catalysts. Our work demonstrates that Co3O4/Ppy/GO is highly active for the ORR. Notably, the Ppy coupling effects between Co3O4 and GO provide a new route for the preparation of efficient non-precious electrocatalysts with hierarchical porous structures for fuel cell applications.

Modified carbothermal reduction method for synthesis of LiFePO_4/C composite

With LiAc-2H2O as Li precursor,pure olivine phase LiFePO4/C was synthesized at a relatively low temperature（650 ℃） and short sintering period（4 h） by molten salt carbothermal reduction method.Scanning electron micrograph shows that particle size of the product is about 1μm,smaller than that of the sample synthesized with Li2CO3 as Li precursor.Electrochemical measurements prove that LiFePO4/C obtained from LiAc-2H2O shows high capacity.The initial discharge capacities are 148 mA-h/g at 0.5C rate and 115 mA-h/g at 5C rate,respectively.After 50 cycles,the capacity retention ratios are 93% and 89% at 0.5C rate and 5C rate,respectively.

Effects of reaction parameters on preparation of Cu nanoparticles via aqueous solution reduction method with NaBH_4

The preparation of Cu nanoparticles by the aqueous solution reduction method was investigated. The effects of different reaction parameters on the preparation of Cu nanoparticles were studied. The optimum conditions for preparing well-dispersed nanoparticles were found as follows: 0.4 mol/L NaBH4 was added into solution containing 0.2 mol/L Cu2+, 1.0% gelatin dispersant in mass fraction, and 1.2 mol/L NH3?H2O at pH 12 and 313 K. In addition, a series of experiments were performed to discover the reaction process. NH3?H2O was found to be able to modulate the reaction process. At pH=10, Cu2+ was transformed to Cu(NH3)42+ as precursor after the addition of NH3?H2O, and then Cu(NH3)42+ was reduced by NaBH4 solution. At pH=12, Cu2+ was transformed to Cu(OH)2 as precursor after the addition of NH3?H2O, and Cu(OH)2 was then reduced by NaBH4 solution.

Atomically dispersed Mn-N_(x) catalysts derived from Mn-hexamine coordination frameworks for oxygen reduction reaction

Metal-organic frameworks recently have been burgeoning and used as precursors to obtain various metal-nitrogen-carbon catalysts for oxygen reduction reaction(ORR).Although rarely studied,Mn-N-C is a promising catalyst for ORR due to its weak Fenton reaction activity and strong graphitization catalysis.Here,we developed a facile strategy for anchoring the atomically dispersed nitrogen-coordinated single Mn sites on carbon nanosheets(MnNCS)from an Mn-hexamine coordination framework.The atomically dispersed Mn-N_(4) sites were dispersed on ultrathin carbon nanosheets with a hierarchically porous structure.The optimized MnNCS displayed an excellent ORR performance in half-cells(0.89 V vs.reversible hydrogen electrode(RHE)in base and 0.76 V vs.RHE in acid in half-wave potential)and Zn-air batteries(233 mW cm^(−2)in peak power density),along with significantly enhanced stability.Density functional theory calculations further corroborated that the Mn-N_(4)-C(12)site has favorable adsorption of*OH as the rate-determining step.These findings demonstrate that the metal-hexamine coordination framework can be used as a model system for the rational design of highly active atomic metal catalysts for energy applications.

Comparison of reduction behavior of Fe_2O_3, ZnO and ZnFe_2O_4 by TPR technique

Advanced integrated gasification combined cycle （IGCC） power generation systems require the development of high-temperature, regenerable, desulfurization sorbents capable of removing hydrogen sulfide from coal gasifier gas to very low levels. As a sort of effective desufurizer, such as Fe2O3, ZnO and ZnFe2O4, it will endure strong reducing atmosphere in desulfurization process. The reduced degree of desufurizer can have an effect on its desulfurization reactivity. In this paper, Fe2O3, ZnO and ZnFe2O4 were synthesized by precipitation or co-precipitation at constant pH. After aging, washing and drying, the solids were calcined at 800℃. The reduction behaviors of sample were characterized by temperature-programmed reduction （TPR）. It is found that there are two reduction peaks for Fe2O3 in TPR, and whereas no reduction peaks for ZnO are found. The reduction process of ZnFe2O4 prepared by co-precipitation is different from that of Fe2O3. ZnFe2O4 is easier to be reduced than Fe2O3. The activation energy of reduction process for Fe2O3 and ZnFe2O4 is obtained at different reduction periods.

CH_4 emissions and reduction potential in wastewater treatment in China

The treatment of domestic and industrial wastewater is one of the major sources of CH_4 in the Chinese waste sector. On the basis of statistical data and country-specific emission factors, using IPCC methodology, the characteristics of CH_4 emissions from wastewater treatment in China were analyzed. The driving factors of CH_4 emissions were studied, and the emission trend and reduction potential were predicted and analyzed according to the current situation. Results show that in 2010, CH_4 emissions from the treatment of domestic and industrial wastewater were0.6110 Mt and 1.6237 Mt, respectively. Eight major industries account for more than 92% of emissions, and CH_4 emissions gradually increased from 2005 to 2010. From the controlling management scenario, we predict that in 2020, CH_4 emissions from the treatment of domestic and industrial wastewater will be 1.0136 Mt and 2.3393 Mt, respectively, and the reduction potential will be 0.0763 Mt and 0.2599 Mt, respectively.From 2010 to 2020, CH_4 emissions from the treatment of domestic and industrial wastewater will increase by 66% and 44%, respectively.