Cooperation between single atom catalyst and support to promote nitrogen electroreduction to ammonia:A theoretical insight

The co-catalysis between single atom catalyst(SAC)and its support has recently emerged as a promising strategy to synergistically boost the catalytic activity of some complex electrochemical reactions,encompassing multiple intermediates and pathways.Herein,we utilized defective BC_(3)monolayer-supported SACs as a prototype to investigate the cooperative effects of SACs and their support on the catalytic performance of the nitrogen reduction reaction(NRR)for ammonia(NH_(3))production.The results showed that these SACs can be firmly stabilized on these defective BC_(3)supports with high stability against aggregation.Furthermore,co-activation of the inert N_(2)reactant was observed in certain embedded SACs and their neighboring B atoms on certain BC3 sheets due to the noticeable charge transfer and significant N–N bond elongation.Our high-throughput screening revealed that the Mo/DV_(CC)and W/DV_(CC)exhibit superior NRR catalytic performance,characterized by a low limiting potential of−0.33 and−0.43 V,respectively,which can be further increased under acid conditions based on the constant potential method.Moreover,varying NRR catalytic activities can be attributed to the differences in the valence state of active sites.Remarkably,further microkinetic modeling analysis displayed that the turnover frequency of N_(2)–to–NH_(3)conversion on Mo/DV_(CC)is as large as 1.20×10^(−3)s^(−1)site^(−1) at 700 K and 100 bar,thus guaranteeing its ultra-fast reaction rate.Our results not only suggest promising advanced electrocatalysts for NRR but also offer an effective avenue to regulate the electrocatalytic performance via the co-catalytic metal–support interactions.

The Electrocatalytic Performance of Rare Earth Ion Doped Co_(0.2)Ni_(0.8)-MOF-74 Catalyst for Nitrogen Reduction

We took Co_(0.2)Ni_(0.8)-MOF-74 with bimetallic synergistic effect as the basic material,and selected rare earth ions Ho,Gd,and Er with ion radii close to Co and Ni as the research objects for doping.The influence of rare earth ion doping amount and doping type on the eNRR performance of the catalyst was explored.The experimental results show that the ammonia yield rate and Faraday efficiency doped with Co_(0.2)Ni_(0.8)-MOF-0.5Ho are the highest,reaching 1.28×10^(-10)mol·s^(-1)·cm^(-2)/39.8%,which is higher than the1.12×10^(-10)mol·s^(-1)·cm^(-2)/32.2%of Co_(0.2)Ni_(0.8)-MOF-74,and is about 14.3%/23.7%higher than that without doping,respectively.And the stability of Co_(0.2)Ni_(0.8)-MOF-0.5 Ho is good(after 80 hours of continuous testing,the current density did not significantly decrease).This is mainly due to doping,which gives Co_(0.2)Ni_(0.8)-MOF-74 a larger specific surface area and catalytic active sites.The catalyst doped at the same time has more metal cation centers,which increases the electron density of the metal centers and enhances the corresponding eNRR performance.

“Blocking and rebalance”mechanism-guided design strategies of bimetallic doped 2D a-phosphorus carbide as efficient catalysts for N_(2) electroreduction

Compared to single atom catalysts(SACs),the introduction of dual atom catalysts(DACs)has a significantly positive effect on improving the efficiency in the electrocatalytic nitrogen reduction reaction(NRR)which provides an environmental alternative to the Haber-Bosch process.However,the research on the mechanism and strategy of designing bimetallic combinations for better performance is still in its early stages.Herein,based on"blocking and rebalance"mechanism,45 combinations of bimetallic pair dopedα-phosphorus carbide(TM_(A)TM_(B)@PC)are investigated as efficient NRR catalysts through density functional theory and machine learning method.After a multi-step screening,the combinations of TiV,TiFe,MnMo,and FeW exhibit highly efficient catalytic performance with significantly lower limiting potentials(-0.17,-0.18,-0.14,and-0.30 V,respectively).Excitingly,the limiting potential for CrMo and CrW combinations is 0 V,which are considered to be extremely suitable for the NRR process.The mechanism of"blocking and rebalance"is revealed by the exploration of charge transfer for phosphorus atoms in electron blocking areas.Moreover,the descriptorφis proposed with machine learning,which provides design strategies and accurate prediction for finding efficient DACs.This work not only offers promising catalysts TM_(A)TM_(B)@PC for NRR process but also provides design strategies by presenting the descriptorφ.

“Capture-activation-recapture” mechanism-guided design of double-atom catalysts for electrocatalytic nitrogen reduction

Compared with the traditional industrial nitrogen fixation, electrocatalytic methods, especially those utilizing double-atom catalysts containing nonmetals, can give good consideration to the economy and environmental protection. However, the existing “acceptance-donation” mechanism is only applicable to bimetallic catalysts and nonmetallic double-atom catalysts containing boron atoms. Herein, a novel “capture-activation-recapture” mechanism for metal-nonmetal double-atom catalyst is proposed to solve the problem by adjusting the coordination environments of nonmetallic atoms and utilizing the activation effect of metal atoms on nitrogen. Based on this mechanism, the nitrogen reduction reaction (NRR) activity of 48 structures is calculated by density functional theory calculation, and four candidates are selected as outstanding electrocatalytic nitrogen reduction catalysts: Si-Fe@NG (U_(L) = –0.14 V), Si-Co@NG (U_(L)= –0.15 V), Si-Mo@BP1 (U_(L) = 0 V), and Si-Re@BP1 (U_(L) = –0.02 V). The analyses of electronic properties further confirm “capture-activation-recapture” mechanism and suggest that the difference in valence electron distribution between metal and Si atoms triggers the activation of N≡N bonds. In addition, a machine learning approach is utilized to generate an expression and an intrinsic descriptor that considers the coordination environment to predict the limiting potential. This study offers profound insight into the synergistic mechanism of TM and Si for NRR and guidance in the design of novel double-atom nitrogen fixation catalysts.

Chromium phosphide nanoparticles embedded in porous nitrogen-/phosphorus-doped carbon as efficient electrocatalysts for a nitrogen reduction reaction

The resource recovery of heavy metals from effluent has significant environmental implications and potential commercial value.Chromium phosphide nanoparticles embedded in a nitrogen-/phosphorus-doped porous carbon matrix(CrP/NPC)are synthesized via a consecutive Cr^(6+)leachate treatment and resource recovery process.Electrochemical testing shows that CrP/NPC shows excellent nitrogen reduction reaction(NRR)performance,which yields the highest NH_(3) production rate of 22.56μg h^(−1) mg^(−1)_(cat).and Faradaic efficiency(16.37%)at−0.5 V versus the reversible hydrogen electrode in a 0.05M Na_(2)SO_(4) aqueous solution,as well as robust catalytic stability.The isotopic experiments using ^(15)N^(2) as a nitrogen source confirm that the detected NH_(3) is derived from the NRR process.Finally,density functional theory(DFT)calculations show that the electron deficiency environment of the Cr site can significantly reduce the barrier of the NRR process and promote the formation of intermediate species.

Nitrogen and Phosphorus Loss Law and Emission Reduction Effects Under Water and Fertilizer Management Integrated Mode in Dike Paddy Field

To achieve the purpose of reducing farm non-point source pollution, we integrated site specific nitrogen management precise irrigation, controlled drainage, and wetland eco-repair system in dike area of Taihu basin. During investigation, it had given prominence for the water and fertilizer coupling effects of precise irrigation and site specific nutrient management, the characteristics of integration on controlled irrigation, controlled drainage and wetland ecosystem non-point source pollution control. Then the water and fertilizer integrated management mode of paddy field was put forward in Taihu basin where the water production efficiency increased to 1.64 kg. m-3, water saved 37.8%, fertilizer use efficiency raised 15,4%, yield raised 10%, and N, P load decreased 26%-72%. The modern agricultural and farmland ecosystems that control and cut down the farm non-point source pollution came into being, which can be a reference by Taihu basin to control its agricultural non-point source pollution and eutrophicated water body.

Subsurface intercalation activating basal plane of black phosphorus for nitrogen reduction

Ammonia(NH3)is not only an important chemical in many fields,but also provides a promising intermediate for energy stor-age[1,2].To produce NH3 from naturally abundant N2,the strong N≡N bond in the inert N2 molecules must be broken firstly.

Enhancing ammonia production rates from electrochemical nitrogen reduction by engineering three-phase boundary with phosphorus-activated Cu catalysts

Electrochemical N_(2) reduction reaction(eNRR) over Cu-based catalysts suffers from an intrinsically low activity of Cu for activation of stable N_(2) molecules and the limited supply of N_(2) to the catalyst due to its low solubility in aqueous electrolytes.Herein,we propose phosphorus-activated Cu electrocatalysts to generate electron-deficient Cu sites on the catalyst surface to promote the adsorption of N_(2) molecules.The eNRR system is further modified using a gas diffusion electrode(GDE) coated with polytetrafluoroethylene(PTFE) to form an effective three-phase boundary of liquid water-gas N_(2)-solid catalyst to facilitate easy access of N_(2) to the catalytic sites.As a result,the new catalyst in the flow-type cell records a Faradaic efficiency of 13.15% and an NH_(3) production rate of 7.69 μg h^(-1) cm^(-2) at-0.2 V_(RHE),which represent 3.56 and 59.2 times increases from those obtained with a pristine Cu electrode in a typical electrolytic cell.This work represents a successful demonstration of dual modification strategies;catalyst modification and N_(2) supplying system engineering,and the results would provide a useful platform for further developments of electrocatalysts and reaction systems.

Mechanism of phosphorus removal in beneficiation of high phosphorous oolitic hematite by direct reduction roasting with dephosphorization agent

High phosphorous oolitic hematite ore is one of typical intractable iron ores in China, and the conventional beneficiation methods are found to be impracticable to , remove phosphorus from the ore effectively. Better beneficiation index were gotten by direct reduction roasting with dephosphorization agent followed by two stages of grinding and magnetic separation. P content decreases from 0.82% in the raw ore to 0.06% in the magnetic concentrate, and the total iron grade increases from 43.65% to 90.23%, the recovery of iron can reach 87%. Mechanisms of phosphorus removal in the beneficiation of high phosphorous oolitic hematite ore by direct reduction roasting with dephosphorization agent were studied using XRD, SEM and EPMA. The results showed that about 20% of the apatite in the raw ore transferred into phosphorus and volatilized with the gas in the process of reduction roasting, while the rest 80% apatite was not involved in the reaction of generation of phosphorus, and remained as apatite in the roasted products, which was removed to tailings by grinding and magnetic separation. A small amount of phosphorus existed in the magnetic concentrate as apatite. The oolitic texture of raw ore was partly changed during roasting, resulting in the formation of nepheline in the reaction between the dephosphorization agent, SiO2 and Al2O3 in the raw ore, which greatly improved the liberation degree of minerals in the roasted products, and it was beneficial to the subsequent grinding and magnetic separation.

Synthesis of a chabazite-supported copper catalyst with full mesopores for selective catalytic reduction of nitrogen oxides at low temperature

A series of meso‐microporous copper‐supporting chabazite molecular sieve（CuSAPO‐34） catalysts with excellent performance in low‐temperature ammonia selective catalytic reduction（NH3‐SCR）have been synthesized via a one‐pot hydrothermal crystallization method. The physicochemical properties of the catalysts were characterized by scanning electron microscopy, transmission electron microscopy, N2 adsorption‐desorption measurements, X‐ray diffraction, 27 Al magic angle spinning nuclear magnetic resonance, diffuse reflectance ultraviolet‐visible spectroscopy, inductively coupled plasma‐atomic emission spectroscopy, X‐ray photoelectron spectroscopy, temperature‐programmed reduction measurements, and electron paramagnetic resonance analysis. The formation of micro‐mesopores in the Cu‐SAPO‐34 catalysts decreases diffusion resistance and greatly improves the accessibility of reactants to catalytic active sites. The main active sites for NH3‐SCR reaction are the isolated Cu^2＋ species displaced into the ellipsoidal cavity of the Cu‐SAPO‐34 catalysts.

Nitrogen-doped TiO_2 microsheets with enhanced visible light photocatalytic activity for CO_2 reduction

Nitrogen-doped anatase TiO 2 microsheets with 65%（001） and 35%（101） exposed faces were fabricated by the hydrothermal method using TiN as precursor in the presence of HF and HCl. The samples were characterized by scanning electron microscopy,X-ray diffraction,N2 adsorption,X-ray photoelectron spectroscopy,UV-visible spectroscopy,and electrochemical impedance spectroscopy. Their photocatalytic activity was evaluated using the photocatalytic reduction of CO2. The N-doped TiO 2 sample exhibited a much higher visible light photocatalytic activity for CO2 reduction than its precursor TiN and commercial TiO 2（P25）. This was due to the synergistic effect of the formation of surface heterojunctions on the TiO 2 microsheet surface,enhanced visible light absorption by nitrogen-doping,and surface fluorination.

Oxygen vacancy enhancing mechanism of nitrogen reduction reaction property in Ru/TiO2

To search the new effective nitrogen reduction reaction(NRR)electrocatalyst is very important for the ammonia-based industry.Herein,we reported the design of a novel NRR electrocatalyst with Ru NPs loaded on oxygen-vacancy TiO2(Ru/TiO2-Vo).Structural characterizations revealed that oxygen vacancy was loaded in the matrix of Ru/TiO2-Vo.Electrocatalytic results indicated that Ru/TiO2-Vo showed good NRR performance(2.11μg h^-1 cm^-2).Contrast tests showed that NRR property of Ru/TiO2-Vo was much better than those of Ru/TiO-12(B)(0.53μg hcm^-2)and Ru/P25(0.42μg h^-1 cm^-2).Furthermore,density functional theory calculation results indicated catalytic mechanism of NRR and rate-determining step(*N2+1/2 H2→*N+*NH)was the potential-determining step with the overpotential requirement of 0.21 V.A combination of electronic structure analysis and catalytic measurement shed light on the synergistic effect of Ru and oxygen vacancy on the NRR performance.

Recovery of iron from high phosphorus oolitic iron ore using coal-based reduction followed by magnetic separation

Oolitic iron ore is one of the most important iron resources. This paper reports the recovery of iron from high phosphorus oolitic iron ore using coal-based reduction and magnetic separation. The influences of reduction temperature, reduction time, C/O mole ratio, and CaO content on the metallization degree and iron recovery were investigated in detail. Experimental results show that reduced products with the metallization degree of 95.82% could be produced under the optimal conditions （i.e., reduction temperature, 1250℃; reduction time, 50 min; C/O mole ratio, 2.0; and CaO content, 10wt%）. The magnetic concentrate containing 89.63wt% Fe with the iron recovery of 96.21% was obtained. According to the mineralogical and morphologic analysis, the iron minerals had been reduced and iron was mainly enriched into the metallic iron phase embedded in the slag matrix in the form of spherical particles. Apatite was also reduced to phosphorus, which partially migrated into the metallic iron phase.

Preparation of nitrogen and sulfur co-doped ultrathin graphitic carbon via annealing bagasse lignin as potential electrocatalyst towards oxygen reduction reaction in alkaline and acid media

Renewable lignin used for synthesizing materials has been proven to be highly potential in specific electrochemistry.Here,we report a simple method to synthesize nitrogen and sulfur co-doped carbon nanosheets by using bagasse lignin,denoted as lignin-derived carbon(LC).By adjusting the ratio of nitrogen source and annealing temperature,we obtained the ultrathin graphitic lignin carbon(LC-4-1000)with abundant wrinkles with high surface area of 1208 m2g_1 and large pore volume of 1.40 cm3g_1.In alkaline medium,LC-4-1000 has more positive half-wave potential and nearly current density compared to commercial Pt/C for oxygen reduction reaction(ORR).More importantly,LC-4-1000 also exhibits comparable activity and superior stability for ORR in acid medium due to its high graphitic N ratio and a direct four electron pathway for ORR.This study develops a cost-effective and highly efficient method to prepare biocarbon catalyst for ORR in fuel cells.

Direct and Indirect Applications of Dielectric Barrier Discharge Plasma to Catalytic Reduction of Nitrogen Oxides from Exhaust Gas

Dielectric barrier discharge （DBD） plasma was utilized to oxidize NO contained in the exhaust gas to NO2, ultimately improve the selective catalytic reduction of nitrogen oxides （NOx）. In the one case, DBD was created directly in the exhaust gas （direct application）, and in the an other case, ozone produced by DBD was injected into the exhaust gas （indirect application）. A comparative study between such direct and indirect applications of DBD plasma was made in terms of the NOx removal efficiency and the energy consumption. The NO2 content in the exhaust gas was changed by the voltage applied to the DBD device （for direct application） or by the amount of ozone added to the exhaust gas （for indirect application）. In both cases, NO was easily oxidized to NO2, and the change in NO2 content largely affected the NOx removal performance of the catalytic reactor placed downstream, where both NO and NO2 were reduced to N2 in the presence of ammonia as the reducing agent. The experiments were primarily concerned with the effect of reaction temperature on the catalytic NOx reduction at various NO2 contents. The direct and indirect applications of DBD were found to remarkably improve the catalytic NOx reduction, especially at low temperatures.

ZrO2 nanoparticles anchored on nitrogen-doped carbon nanosheets as efficient catalyst for electrochemical CO2 reduction

Electrochemical reduction of CO2 to produce value-added feedstock chemicals using high-performance electrocatalysts is a promising protocol to address the excessive CO2 in the atmosphere and the energy crisis. However, the high overpotential, low current density, and poor product selectivity for CO2 electroreduction greatly impede their practical applications. In this work, we develop an efficient catalyst for CO2 reduction to CO consisting of well-dispersed ZrO2 nanoparticles tightly anchored on nitrogendoped carbon nanosheets(ZrO2/N-C) for the first time. Importantly, the ZrO2 nanoparticles possess oxygen vacancies and defects, which regulate the electronic structure of catalyst and thus greatly enhance the electrocatalytic activity. Specifically, ZrO2/N-C demonstrates a high CO Faradaic efficiency(FE) of 64% at-0.4 V vs. the reversible hydrogen electrode(RHE) and a respectable current density of ~2.6 m A cm-2 in CO2-saturated 0.5 M KHCO 3 solution. This work opens a new avenue for developing excellent catalysts for CO2 electroreduction with metal oxide/heteroatom-doped carbon composite structure.

Nitrogen doped tin oxide nanostructured catalysts for selective electrochemical reduction of carbon dioxide to formate

Tin/tin oxide materials are key electrocatalysts for selective conversion of CO;to formate/formic acid.Herein we report a tin oxide material with nitrogen doping by using ammonia treatment at elevated temperature. The N doped material demonstrated enhanced electrocatalytic CO;reduction activity, showing high Faradaic efficiency（90%） for formate at -0.65 V vs. RHE with partial current density of 4 mA/cm;.The catalysis was contributed to increased electron negativity of N atom compared to O atom. Additionally, the N-doped catalyst demonstrates sulfur tolerance with retained formate selectivity. The analysis after electrolysis shows that the catalyst structure partially converts to metallic Sn, and thus the combined Sn/N-SnO;is the key for the active CO;catalysis.

Distribution behavior of phosphorus in the coal-based reduction of high-phosphorus-content oolitic iron ore

This study focuses on the reduction of phosphorus from high-phosphorus-content oolitic iron ore via coal-based reduction. The distribution behavior of phosphorus （i.e., the phosphorus content and the phosphorus distribution ratio in the metal, slag, and gas phases） during reduction was investigated in detail. Experimental results showed that the distribution behavior of phosphorus was strongly influenced by the reduction temperature, the reduction time, and the C/O molar ratio. A higher temperature and a longer reaction time were more favor-able for phosphorus reduction and enrichment in the metal phase. An increase in the C/O ratio improved phosphorus reduction but also hin-dered the mass transfer of the reduced phosphorus when the C/O ratio exceeded 2.0. According to scanning electron microscopy analysis, the iron ore was transformed from an integral structure to metal and slag fractions during the reduction process. Apatite in the ore was reduced to P, and the reduced P was mainly enriched in the metal phase. These results suggest that the proposed method may enable utilization of high-phosphorus-content oolitic iron ore resources.

Migration behaviors and kinetics of phosphorus during coal-based reduction of high-phosphorus oolitic iron ore

To understand the migration mechanisms of phosphorus(P)during coal-based reduction,a high-phosphorus oolitic iron ore was reduced by coal under various experimental conditions.The migration characteristics and kinetics of P were investigated by a field-emission electron probe microanalyzer(FE-EPMA)and using the basic principle of solid phase mass transfer,respectively.Experimental results showed that the P transferred from the slag to the metallic phase during reduction,and the migration process could be divided into three stages:phosphorus diffusing from the slag to the metallic interface,the formation of Fe P compounds at the slag metal interface and P diffusing from the slag metal interface to the metallic interior.The reduction time and temperature significantly influenced the phosphorus content of the metallic and slag phases.The P content of the metallic phase increased with increasing reduction time and temperature,while that of the slag phase gradually decreased.The P diffusion constant and activation energy were determined and a migration kinetics model of P in coal-based reduction was proposed.P diffusion in the metallic phase was the controlling step of the P migration.

Theoretical screening of the transition metal heteronuclear dimer anchored graphdiyne for electrocatalytic nitrogen reduction

Developing efficient electrocatalysts for nitrogen reduction reaction(NRR)is crucial to replace the both energy-intensive and environment-malignant Haber-Bosch process.Here using density functional theory calculations,we systematically studied the potential of the heteronuclear 3 d transition metal dimers anchored graphdiyne monolayers(FeM@and NiM@GDY,M=Ti,V,Cr,Mn,Fe,Co,Ni,and Cu)as efficient NRR catalysts.Among all the studied double-atom catalysts(DACs),FeCo@and NiCo@GDY are the most promising with excellent NRR catalytic activity,high ability to suppress the competing hydrogen evolution reaction(HER),and good stability.For both FeCo@and NiCo@GDY,NRR prefers to the distal pathway with the calculated onset potentials of -0.44 and -0.36 V,respectively,which are comparable and even better than their homonuclear counterparts.Moreover,FeCo@and NiCo@GDY have higher ability to suppress HER than Fe_(2)@ and Co_(2)@GDY,which may result from the modulated d state electronic structure due to the synergy effect of the heteronuclear atoms in the DACs.Our work not only suggests that FeCo@and NiCo@GDY hold great promises as efficient,low-cost,and stable DACs for NRR,but also further provides a strategy,i.e.alloying the atomic metal catalysts,to improve the NRR catalytic activity and/or selectivity.