Efficiently utilizing ammonia(carbon-free fuel)via low-temperature fuel cells is severely hindered by the sluggish kinetics of ammonia oxidation reaction(AOR).Herein,platinum-iridium-tungsten nanocubes(PtIrW-NCBs)with...Efficiently utilizing ammonia(carbon-free fuel)via low-temperature fuel cells is severely hindered by the sluggish kinetics of ammonia oxidation reaction(AOR).Herein,platinum-iridium-tungsten nanocubes(PtIrW-NCBs)with exposed{100}-rich facets were synthesized by a glucose-assisted solvent-thermal method,in which alloying W not only can facilitate the formation of such specific nanostructures to expose more active sites for AOR,but also modulate the electronic structure of PtIr to promote the kinetics of AOR.The PtIrW-NCBs featuring the small nanoparticle size of 5.05±0.07 nm exhibit superior AOR performance,wherein the onset potential is down to 0.319 V and the mass activity is 30.15 A g_((PGM=Pt,Ir))^(-1)at 0.50 V vs.RHE,significantly higher than those of reported majority of AOR catalysts and even commercial PtIr/C.Meanwhile,in situ Fourier transform infrared spectroscopy measurement further reveals that AOR on PtIrW-NCBs dominantly undergoes the dimerization path of NH_(x)(1≤x≤2).In addition,the theoretical calculations also identify that alloying W into PtIr can contribute additional electrons to 5d orbitals of PtIr,enabling the d-band center approaching the Femi level,which in turn induces the high-filling of bonding orbitals of N-N bond in^(*)N_(2)H_(4),promoting the dimerization of^(*)NH_(2)to^(*)N_(2)H_(4)and thus leading to high AOR activity of PtIrW.This work provides new insights for designing efficient AOR electrocatalysts.展开更多
As an emergent energy carrier,ammonia benefits from a well-established industrial infrastructure for its transportation and production,positioning it as a promising candidate toward a carbon-free energy landscape.With...As an emergent energy carrier,ammonia benefits from a well-established industrial infrastructure for its transportation and production,positioning it as a promising candidate toward a carbon-free energy landscape.Within this context,the electrocatalytic ammonia oxidation reaction(AOR)is pivotal.Platinum(Pt),recognized as the most efficient AOR catalyst,has undergone extensive development over the years,yielding notable advancements across various domains,ranging from elucidating the reaction mechanism to exploring innovative materials.This review begins by elucidating the mechanism of ammonia oxidation,summarizing the evolution of the mechanism and the diverse intermediates identified through various detection methods.Subsequently,it outlines the research progress surrounding different Pt-based catalysts,followed by a discussion on standard protocols for electrochemical ammonia oxidation testing,which facilitates meaningful comparisons across studies and catalyzes the development of more efficient and potent catalysts.Moreover,the review addresses current challenges in ammonia oxidation and outlines potential future directions,providing a comprehensive outlook on the field.展开更多
Mining,smelting and tailing deposition activities can cause metal(loid)contamination in surrounding soils,threatening ecosystems and human health.Microbial indicators are sensitive to environmental factors and have a ...Mining,smelting and tailing deposition activities can cause metal(loid)contamination in surrounding soils,threatening ecosystems and human health.Microbial indicators are sensitive to environmental factors and have a crucial role in soil ecological risk assessment.Xikuangshan,the largest active antimony(Sb)mine in the world,was taken as the research area.The soil properties,metal(loid)contents and microbial characteristics were investigated and their internal response relationships were explored by multivariate statistical analysis.The assessment of the single pollution index and Nemerow synthetic pollution index(PN)showed that the soils were mainly polluted by Sb,followed by Cd and As,in which sampling site S1 had a slight metal(loid)pollution and the other sampling sites suffered from severe synthetic metal(loid)pollution.The microbial characteristics were dissimilar among sampling points at different locations from the mining area according to hierarchical cluster analysis.The correlation analysis indicated that fluorescein diacetate hydrolase,acid phosphatase,soil basal respiration andmicrobial biomass carbonwere negatively correlatedwith PN,indicating their sensitivity to combined metal(loid)contamination;that dehydrogenase was positively correlated with pH;and that urease,potential ammonia oxidation and abundance of ammonia-oxidizing bacteria and archaea were correlated with N(nitrogen)contents.However,β-glucosidase activity had no significant correlations with physicochemical properties and metal(loid)contents.Principal components analysis suggested bioavailable Sb and pH were the dominant factors of soil environment in Xikuangshan Sb mining area.Our results can provide a theoretical basis for ecological risk assessment of contaminated soil.展开更多
Soil arsenic contamination is of great concern because of its toxicity to human,crops,and soil microorganisms.However,the impacts of arsenic on soil ammonia oxidizers communities remain unclear.Seven types of soil spi...Soil arsenic contamination is of great concern because of its toxicity to human,crops,and soil microorganisms.However,the impacts of arsenic on soil ammonia oxidizers communities remain unclear.Seven types of soil spiked with 0 or 100 mg arsenic per kg soil were incubated for 180 days and sampled at days 1,15,30,90 and 180.The changes in the community composition and abundance of ammonia oxidizing bacteria(AOB)and ammonia oxidizing archaea(AOA)were analyzed by terminal restriction fragment length polymorphism(TRFLP)analysis,clone library sequencing,and quantitative PCR(qPCR)targeting amoA gene.Results revealed considerable variations in the potential ammonia oxidation(PAO)rates in different soils,but soil PAO was not consistently significantly inhibited by arsenic,probably due to the low bioavailable arsenic contents or the existence of functional redundancy between AOB and AOA.The variations in AOB and AOA communities were closely associated with the changes in arsenic fractionations.The amoA gene abundances of AOA increased after arsenic addition,whereas AOB decreased,which corroborated the notion that AOA and AOB might occupy different niches in arsenic-contaminated soils.Phylogenetic analysis of amoA gene-encoded proteins revealed that all AOB clone sequences belonged to the genus Nitrosospira,among which those belonging to Nitrosospira cluster 3a were dominant.The main AOA sequence detected belonged to Thaumarchaeal Group 1.1b,which was considered to have a high ability to adapt to environmental changes.Our results provide new insights into the impacts of arsenic on the soil nitrogen cycling.展开更多
Over recent decades,fuel cell technologies have emerged as viable solutions to address the energy and environmental challenges stemming from fossil fuel dependence.Especially,ammonia has gained increasing attention as...Over recent decades,fuel cell technologies have emerged as viable solutions to address the energy and environmental challenges stemming from fossil fuel dependence.Especially,ammonia has gained increasing attention as an attractive alternative to hydrogen,offering comparable energy density while maintaining carbon-free characteristics,along with superior storage and transport properties that give direct ammonia fuel cells(DAFCs)distinct safety advantages over hydrogen-based systems.Central to this technology is the anodic ammonia oxidation reaction(AOR),where platinum(Pt)remains the most efficient catalyst after years of intensive research.This review offers a comprehensive overview of Ptbased AOR electrocatalysts with potential for application in low-temperature DAFCs.Following an introductory section highlighting key historical developments and catalytic breakthroughs,a fundamental understanding of low-temperature DAFC operation and AOR mechanisms is systematically presented.Subsequently,it outlines the advancements in Pt-based catalysts from simple monometallic systems to sophisticated multimetallic alloys and composites,highlighting material innovations and performance enhancements.Afterward,key challenges and future research directions for advancing AOR electrocatalysts are identified,with the aim of providing valuable guidance for developing practical,highperformance,and low-temperature DAFC systems.展开更多
Electrochemical nitrogen looping represents a promising carbon-free and sustainable solution for the energy transition,in which electrochemical ammonia oxidation stays at the central position.However,the various nitro...Electrochemical nitrogen looping represents a promising carbon-free and sustainable solution for the energy transition,in which electrochemical ammonia oxidation stays at the central position.However,the various nitrogen-containing intermediates tend to poison and corrode the electrocatalysts,even the state-of-the-art noble-metal ones,which is worsened at a high applied potential.Herein,we present an ultrarapid laser quenching strategy for constructing a corrosion-resistant and nanostructured CuNi alloy metallic glass electrocatalyst.In this material,single-atom Cu species are firmly bonded with the surrounding Ni atoms,endowing exceptional resistance against ammonia corrosion relative of conventional CuNi alloys.Remarkably,a record-high durability for over 300 h is achieved.Ultrarapid quenching also allows a much higher Cu content than typical single-atom alloys,simultaneously yielding a high rate and selectivity for ammonia oxidation reaction(AOR).Consequently,an outstanding ammonia conversion rate of up to 95%is achieved with 91.8%selectivity toward nitrite after 8 h.Theoretical simulations reveal that the structural amorphization of CuNi alloy could effectively modify the electronic configuration and reaction pathway,generating stable singleatom Cu active sites with low kinetic barriers for AOR.This ultrarapid laser quenching strategy thus provides a new avenue for constructing metallic glasses with well-defined nanostructures,presenting feasible opportunities for performance enhancement for AOR and other electrocatalytic processes.展开更多
Heterotrophic nitrifiers are bacteria that aerobically oxidize ammonia in the presence of organic carbon sources,which differs from autotrophic nitrifiers that extract energy from ammonia oxidation for cell metabolism...Heterotrophic nitrifiers are bacteria that aerobically oxidize ammonia in the presence of organic carbon sources,which differs from autotrophic nitrifiers that extract energy from ammonia oxidation for cell metabolism and growth.The physiological significance of heterotrophic ammonia oxidation remains unclear,even though this process has been known for decades.Here,we demonstrate that direct ammonia oxidation(Dirammox)—a heterotrophic ammonia oxidation process with dinitrogen(N)as the primary product—is associated with both redox balance and the electron transport chain in A/caligenes faecalis.Genetic and proteomic studies indicated that disruption of Dirammox genes(dnfA/dnfB/dnfC)induces a transient redox imbalance and perturbation in energy metabolism,further resulting in delayed growth.In addition,we found via biochemical and physiological studies that endogenous reactive oxygen species(ROS)enhance redox fluxes to ammonia oxidation,and the genetic disruption of cytochrome c peroxidase results in an increased flux of electrons to ammonia oxidation,producing N_(2) and N_(2)O.These unexpected findings provide a more thorough understanding of both the Dirammox process and the physiology of heterotrophic ammonia oxidation.展开更多
As a promising fuel candidate,ammonia has been successtully used as anode feed in alkaline fuel cells.However,current technology in catalysts for ammonia electro-oxidation reaction(AOR)with respect to both cost and pe...As a promising fuel candidate,ammonia has been successtully used as anode feed in alkaline fuel cells.However,current technology in catalysts for ammonia electro-oxidation reaction(AOR)with respect to both cost and performance is inadequate to ensure large scale commercial application of direct ammonia fuel cells.Recent studies found that alloying Pt with different transition metals and controlling the morphology of catalysts can improve the AOR activity,and thus potentially can solve the cost issue.Herein,(100)-terminated Pt-M nanocubes(M=3d-transition metals Fe,Co,Ni,Zn)are synthesized via wet-chemistry method and their catalytic activities toward AOR are evaluated.The addition of Fe,Co,Ni and Zn elements can enhance the AOR activity due to decrease in oxophilicity of platinum and bifunctional mechanism.Pt-Zn exhibits the maximum mass activity and specific ativity with values of 0.41 A/mgpt and 169 mA/cm2 that are 1.6 and 1.8 times higher than Pt nanocubes,respectively.Pt-Fe,Pt-Co and PI-Ni nanocubes also ilustrate higher mass and specific activities compared to Pt nanocubes.展开更多
Electrocatalytic ammonia oxidation reaction(EAOR)provides an ideal solution for on-board hydrogen supply for fuel cells,while the lack of efficient and durable EAOR catalysts has been a long-standing obstacle for its ...Electrocatalytic ammonia oxidation reaction(EAOR)provides an ideal solution for on-board hydrogen supply for fuel cells,while the lack of efficient and durable EAOR catalysts has been a long-standing obstacle for its practical application.Herein,we reported that the defect engineering via in-situ electrochemically introducing oxygen vacancies(Vo)not only turns the inactive CuO into efficient EAOR catalyst but also achieves a high stability of over 400 h at a high current density of~200 mA·cm^(−2).Theoretical simulation reveals that the presence of Vo on the CuO surface induces a remarkable upshift of the d-band center of active Cu site closer to the Fermi level,which significantly stabilizes the reaction intermediates(*NHx)and efficiently oxidizes NH3 into N2.This Vo-modulated CuO shows a different catalytic mechanism from that on the conventional Pt-based catalysts,paving a new avenue to develop inexpensive,efficient,and robust catalysts,not limited to EAOR.展开更多
It is still a lack of bifunctional catalysts for ammonia oxidation reaction(AOR)and hydrogen evolution reaction(HER)due to their different reaction mechanisms.In this work,P is doped into PtZn alloy by calcination wit...It is still a lack of bifunctional catalysts for ammonia oxidation reaction(AOR)and hydrogen evolution reaction(HER)due to their different reaction mechanisms.In this work,P is doped into PtZn alloy by calcination with NaH_(2)PO_(2) as P source to induce the lattice tensile strain of Pt and the electronic interaction between P and Zn,which optimizes the AOR and HER activity simultaneously.The sample with the optimal P content can drive the AOR peak current density of 293.6 mA·mgPt^(-1),which is almost 2.7 times of Pt.For HER,the overpotential at^(-1)0 mA·cm^(-2) is only 23 mV with Tafel slope of 34.1 mV·dec^(-1).Furthermore,only 0.59 V is needed to obtain 50 mA·mgPt^(-1) for ammonia electrolysis under a two-electrode system.Therefore,this work shows an ingenious method to design bifunctional catalysts for ammonia electrolysis.展开更多
Ammonia-oxidizing archaeon(AOA)could play important roles for nitrogen removal in the bioreactors under conditions such as low pH and low dissolved oxygen.Therefore,enhancing ammonia oxidation capability of AOA has gr...Ammonia-oxidizing archaeon(AOA)could play important roles for nitrogen removal in the bioreactors under conditions such as low pH and low dissolved oxygen.Therefore,enhancing ammonia oxidation capability of AOA has great significance for water and wastewater treatment,especially under conditions like low dissolved oxygen concentration.Utilizing a novel AOA strain SAT1,which was enriched from a wastewater treatment plant by our group,the effect of magnetic field on AOA’s ammonia oxidation capability,its magnetotaxis and heredity were investigated in this study.Compared with control experiment,AOA’s maximum nitrite-N formation rate during the cultivation increased by 56.8%(0.65 mgN/(L·d))with 20 mT magnetic field.Also,it was testified that AOA possessed a certain magnetotaxis.However,results manifested that the enhancement of AOA’s ammonia oxidation capability was not heritable,that is,lost once the magnetic field was removed.Additionally,the possible mechanism of improving AOA’s ammonia oxidation capability by magnetic field was owing to the promotion of AOA single cells’growth and fission,rather than the enhancement of their ammonia oxidation rates.The results shed light on the application of AOA and methods to enhance AOA’s ammonia oxidation capability,especially in wastewater treatment processes under certain conditions.展开更多
Measurement and predicted variations of ammonia oxidation rate(AOR)are critical for the optimization of biological nitrogen removal,however,it is difficult to predict accurate AOR based on current models.In this study...Measurement and predicted variations of ammonia oxidation rate(AOR)are critical for the optimization of biological nitrogen removal,however,it is difficult to predict accurate AOR based on current models.In this study,a modified model was developed to predict AOR based on laboratoryscale tests and verified through pilot-scale tests.In biological nitrogen removal reactors,the specific ammonia oxidation rate(SAOR)was affected by both mixed liquor volatile suspended solids(MLVSS)concentration and temperature.When MLVSS increased 1.6,4.2,and 7.1-fold(1.3‒8.9 g/L,at 20℃),the measured SAOR decreased by 21%,49%,and 56%,respectively.Thereby,the estimated SAOR was suggested to modify when MLVSS changed through a power equation fitting.In addition,temperature coefficient(θ)was modified based on MLVSS concentration.These results suggested that the prediction of variations ammonia oxidation rate in real wastewater treatment system could be more accurate when considering the effect of MLVSS variations on SAOR.展开更多
Electrocatalytic ammonia oxidation reaction(eAOR)is of significance to ammonia fuel economy and the production of valuable N-containing products,such as nitrite,nitrate and hydrazine.The study of well-defined molecula...Electrocatalytic ammonia oxidation reaction(eAOR)is of significance to ammonia fuel economy and the production of valuable N-containing products,such as nitrite,nitrate and hydrazine.The study of well-defined molecular catalysts offers rich insights in terms of the detailed mechanism of ammonia oxidation.This review analyzes the thermodynamics of ammonia oxidation reactions and summarizes the current progress in molecular electrocatalysts in this booming field.We emphasized the factors that influence the selectivity of products and further discussed the challenges in designing efficient catalysts.展开更多
The oxophilicity of metal oxides is usually utilized to improve the ammonia oxidation reaction(AOR)activity of Pt-based catalysts.But the effect of strong interaction between Pt and metal oxides on AOR is not studied....The oxophilicity of metal oxides is usually utilized to improve the ammonia oxidation reaction(AOR)activity of Pt-based catalysts.But the effect of strong interaction between Pt and metal oxides on AOR is not studied.Herein,experimental and density functional theory calculation results indicate that a strong interaction is built between Pt and reducible CeOx by high-temperature reduction,which induces the electronic interaction due to the difference of work fu nction,then optimizing the competitive adsorption behavior of*OH and*NH_(3)based on hard-soft acid-base principle.Accordingly,the optimal sample achieves an AOR peak current density of 329 mA mg_(Pt)^(-1),which is 2.4 times that of Pt.Meanwhile,it also shows satisfied hydrogen evolution reaction activity with an overpotential of only 24.3 mV at-10 mA cm^(-2)due to the optimization of*H adsorption energy on Pt by CeO_(x).Therefore,this work proposes an AOR activity enhancement mechanism of metal oxides in terms of the strong interaction,and sheds light on developing effective bifunctional catalysts for ammonia electrolysis.展开更多
Monte Carlo method is applied to investigate the kinetics of ammonia oxidative decomposition over the commercial propylene ammoxidation catalyst(Mo-Bi). The simulation is quite in agreement with experimental results. ...Monte Carlo method is applied to investigate the kinetics of ammonia oxidative decomposition over the commercial propylene ammoxidation catalyst(Mo-Bi). The simulation is quite in agreement with experimental results. Monte Carlo simulation proves that the process of ammonia oxidation decomposition is a two-step reaction.展开更多
A range of plant species produce root exudates that inhibit ammonia-oxidizing microorganisms.This biological nitrification inhibition(BNI)capacity can decrease N loss and increase N uptake from the rhizosphere.This st...A range of plant species produce root exudates that inhibit ammonia-oxidizing microorganisms.This biological nitrification inhibition(BNI)capacity can decrease N loss and increase N uptake from the rhizosphere.This study sought evidence for the existence and magnitude of BNI capacity in canola(Brassica napus).Seedlings of three canola cultivars,Brachiaria humidicola(BNI positive)and wheat(Triticum aestivum)were grown in a hydroponic system.Root exudates were collected and their inhibition of the ammonia oxidizing bacterium,Nitrosospira multiformis,was tested.Subsequent pot experiments were used to test the inhibition of native nitrifying communities in soil.Root exudates from canola significantly reduced nitrification rates of both N.multiformis cultures and native soil microbial communities.The level of nitrification inhibition across the three cultivars was similar to the well-studied high-BNI species B.humidicola.BNI capacity of canola may have implications for the N dynamics in farming systems and the N uptake efficiency of crops in rotational farming systems.By reducing nitrification rates canola crops may decrease N losses,increase plant N uptake and encourage microbial N immobilization and subsequently increase the pool of organic N that is available for mineralization during the following cereal crops.展开更多
In this work,the CuAl-LDO/c-CNTs catalyst was fabricated via in situ oriented assembly of layered-double hydroxides(LDHs)and citric acid-modified carbon nanotubes(c-CNTs)followed by annealing treatment,and evaluated i...In this work,the CuAl-LDO/c-CNTs catalyst was fabricated via in situ oriented assembly of layered-double hydroxides(LDHs)and citric acid-modified carbon nanotubes(c-CNTs)followed by annealing treatment,and evaluated in the selective catalytic oxidation(SCO)of NH_(3)to N_(2).The CuAl-LDO/c-CNTs catalyst presented better catalytic performance(98%NH_(3)conversion with nearly 90%N_(2)selectivity at 513 K)than other catalysts,such as CuAlO_(x)/CNTs,CuAlO_(x)/c-CNTs and CuAl-LDO/CNTs.Multiple characterizations were utilized to analyze the difference of physicochemical properties among four catalysts.XRD,TEM and XPS analyses manifested that CuO and Cu_(2)O nanoparticles dispersed well on the surface of the Cu Al-LDO/c-CNTs catalyst.Compared with other catalysts,larger specific surface area and better dispersion of CuAl-LDO/c-CNTs catalyst were conducive to the exposure of more active sites,thus improving the redox capacity of the active site and NH_(3)adsorption capacity.In-situ DRIFTS results revealed that the internal selective catalytic reduction(iSCR)mechanism was found over CuAl-LDO/c-CNTs catalyst.展开更多
Ce1-xZrxO_(2) composite oxides(molar,x=0-1.0,interval of 0.2)were prepared by a cetyltrimethylammonium bromide-assisted precipitation method.The enhancement of silver-species modification and catalytic mechanism of ad...Ce1-xZrxO_(2) composite oxides(molar,x=0-1.0,interval of 0.2)were prepared by a cetyltrimethylammonium bromide-assisted precipitation method.The enhancement of silver-species modification and catalytic mechanism of adsorption-transformationdesorption process were investigated over the Ag-impregnated catalysts for lowtemperature selective catalytic oxidation of ammonia(NH_(3)-SCO).The optimal 5 wt.%Ag/Ce_(0.6)Zr_(0.4)O_(2) catalyst presented good NH_(3)-SCO performancewith>90% NH_(3) conversion at temperature(T)≥250°C and 89% N_(2) selectivity.Despite the irregular block shape and underdeveloped specific surface area(∼60m2/g),the naked and Ag-modified Ce_(0.6)Zr_(0.4)O_(2) solid solution still obtained highly dispersed distribution of surface elements analyzed by scanning electron microscope-energy dispersive spectrometer(SEM-EDS)(mapping),N_(2) adsorptiondesorption test and X-ray diffraction(XRD).H2 temperature programmed reduction(H2-TPR)and X-ray photoelectron spectroscopy(XPS)results indicated that Ag-modification enhanced the mobility and activation of oxygen-species leading to a promotion on CeO_(2) reducibility and synergistic Ag0/Ag+and Ce^(4+)/Ce^(3+)redox cycles.Besides,Ag+/Ag_(2)O clusters could facilitate the formation of surface oxygen vacancies that was beneficial to the adsorption and activation of ammonia.NH3-temperature programmed desorption(NH_(3)-TPD)showed more adsorption-desorption capacity to ammoniawere provided by physical,weakandmedium-strong acid sites.Diffused reflectance infrared Fourier transform spectroscopy(DRIFTS)experiments revealed the activation of ammonia might be the control step of NH3-SCO procedure,during which NH3 dehydrogenation derived from NHx-species and also internal selective catalytic reduction(i-SCR)reactions were proposed.展开更多
[Objective] This study aimed to investigate the abundance and composition of ammonia-oxidizing bacteria and ammonia-oxidizing archaea in Pearl River Estuary sediment.[Method] Firstly,the amoA gene library was construc...[Objective] This study aimed to investigate the abundance and composition of ammonia-oxidizing bacteria and ammonia-oxidizing archaea in Pearl River Estuary sediment.[Method] Firstly,the amoA gene library was constructed;then based on that,the content and diversity of amoA genes of ammonia-oxidizing bacteria and ammonia-oxidizing archaea in Pearl River Estuary sediment were detected by using quantitative real-time polymerase chain reaction（Q-PCR）.[Result] The results of Q-PCR presented that ammonia-oxidizing archaea（AOA） were more abundant than ammonia-oxidizing bacteria（AOB） in the top of sediment cores,with ratios of AOA to AOB of 22 and 9 at the two sites.It suggested that ammonia-oxidizing archaea may play more important roles than ammonia-oxidizing bacteria in the process of ammonia oxidation in the Pearl River Estuary sediment.The phylogenetic tree based on amoA gene sequences revealed that the amoA sequences of both AOA and AOB shared high similarity with the clones from uncultured environment.In the top sediment layer at site Q7,AOB amoA-like gene sequences were dominated by Nitrosomonas-like sequence types,which could be classified into five groups（clusters A,B,C,D and E）.Cluster A accounted for 72.1% of the library.In the top sediment layer,the AOA amoA gene fell into two groups ＂water column/sediment＂ cluster（52.2%） and ＂soil/sediment＂ cluster（47.8%）.But in the bottom sediment layer of Q7,most of the AOA amoA sequences（93.3%） fell into ＂soil/sediment＂ cluster,and a little part（6.7%） fell into the ＂water/sediment＂ cluster.In addition,the total amount of amoA genes in the bottom sediment was higher than that in top sediment.[Conclusion] This study helps to realize the cycle of nitrogen in Pearl River Estuary Region,and thus to provide theoretical support for the treatment of nitrogen eutrophication.展开更多
Small-crystal TS-1 was synthesized via a seed-induced approach using ammonia as the alkali source and tetrapropylammonium bromide as an auxiliary structure-directing agent. The TS-1 samples were characterized using X-...Small-crystal TS-1 was synthesized via a seed-induced approach using ammonia as the alkali source and tetrapropylammonium bromide as an auxiliary structure-directing agent. The TS-1 samples were characterized using X-ray diffraction, N2 adsorption-desorption, Fourier-transform infrared spectroscopy, inductively coupled plasma atomic emission spectroscopy, scanning electron microscopy, and ultraviolet-visible spectroscopy. The use of the colloidal seed reduced the crystal size, and an appropriate amount of silicalite-1 seed assisted Ti incorporation into the TS-1 framework. This method reduces the cost of TS- 1 synthesis because a significantly smaller amount of tetrapropylammonium hydroxide is used. The catalytic performance of the synthesized small-crystal TS-1 samples in cyclohexanone ammoximation was better than that of bulk TS-1 as a result of improved diffusion and a larger number of active tetrahedral Ti centers.展开更多
基金supported by the National Natural Science Foundation of China(22379031)the Guangxi Science and Technology Project of China(AB16380030)+1 种基金the National Research Foundation,SingaporeA*STAR(Agency for Science,Technology and Research)under its LCER Phase 2 Programme Hydrogen&Emerging Technologies FI,Directed Hydrogen Programme(U2305D4003)。
文摘Efficiently utilizing ammonia(carbon-free fuel)via low-temperature fuel cells is severely hindered by the sluggish kinetics of ammonia oxidation reaction(AOR).Herein,platinum-iridium-tungsten nanocubes(PtIrW-NCBs)with exposed{100}-rich facets were synthesized by a glucose-assisted solvent-thermal method,in which alloying W not only can facilitate the formation of such specific nanostructures to expose more active sites for AOR,but also modulate the electronic structure of PtIr to promote the kinetics of AOR.The PtIrW-NCBs featuring the small nanoparticle size of 5.05±0.07 nm exhibit superior AOR performance,wherein the onset potential is down to 0.319 V and the mass activity is 30.15 A g_((PGM=Pt,Ir))^(-1)at 0.50 V vs.RHE,significantly higher than those of reported majority of AOR catalysts and even commercial PtIr/C.Meanwhile,in situ Fourier transform infrared spectroscopy measurement further reveals that AOR on PtIrW-NCBs dominantly undergoes the dimerization path of NH_(x)(1≤x≤2).In addition,the theoretical calculations also identify that alloying W into PtIr can contribute additional electrons to 5d orbitals of PtIr,enabling the d-band center approaching the Femi level,which in turn induces the high-filling of bonding orbitals of N-N bond in^(*)N_(2)H_(4),promoting the dimerization of^(*)NH_(2)to^(*)N_(2)H_(4)and thus leading to high AOR activity of PtIrW.This work provides new insights for designing efficient AOR electrocatalysts.
基金the National Key Research and Development Program of China(No.2022YFB4102000)the National Natural Science Foundation of China(Nos.22102018 and 52171201)+5 种基金the Huzhou Science and Technology Bureau(No.2022GZ45)the China Postdoctoral Science Foundation-Funded Project(No.2022M710601)the Huzhou Science and Technology Bureau(No.2023GZ02)the Natural Science Foundation of Sichuan Province(No.24NSFSC5779)the National Natural Science Foundation of China(Nos.22322201 and 22278067)the Natural Science Foundation of Sichuan Province(No.2023NSFSC0094)。
文摘As an emergent energy carrier,ammonia benefits from a well-established industrial infrastructure for its transportation and production,positioning it as a promising candidate toward a carbon-free energy landscape.Within this context,the electrocatalytic ammonia oxidation reaction(AOR)is pivotal.Platinum(Pt),recognized as the most efficient AOR catalyst,has undergone extensive development over the years,yielding notable advancements across various domains,ranging from elucidating the reaction mechanism to exploring innovative materials.This review begins by elucidating the mechanism of ammonia oxidation,summarizing the evolution of the mechanism and the diverse intermediates identified through various detection methods.Subsequently,it outlines the research progress surrounding different Pt-based catalysts,followed by a discussion on standard protocols for electrochemical ammonia oxidation testing,which facilitates meaningful comparisons across studies and catalyzes the development of more efficient and potent catalysts.Moreover,the review addresses current challenges in ammonia oxidation and outlines potential future directions,providing a comprehensive outlook on the field.
基金supported by the National Natural Science Foundation of China(No.42030706).
文摘Mining,smelting and tailing deposition activities can cause metal(loid)contamination in surrounding soils,threatening ecosystems and human health.Microbial indicators are sensitive to environmental factors and have a crucial role in soil ecological risk assessment.Xikuangshan,the largest active antimony(Sb)mine in the world,was taken as the research area.The soil properties,metal(loid)contents and microbial characteristics were investigated and their internal response relationships were explored by multivariate statistical analysis.The assessment of the single pollution index and Nemerow synthetic pollution index(PN)showed that the soils were mainly polluted by Sb,followed by Cd and As,in which sampling site S1 had a slight metal(loid)pollution and the other sampling sites suffered from severe synthetic metal(loid)pollution.The microbial characteristics were dissimilar among sampling points at different locations from the mining area according to hierarchical cluster analysis.The correlation analysis indicated that fluorescein diacetate hydrolase,acid phosphatase,soil basal respiration andmicrobial biomass carbonwere negatively correlatedwith PN,indicating their sensitivity to combined metal(loid)contamination;that dehydrogenase was positively correlated with pH;and that urease,potential ammonia oxidation and abundance of ammonia-oxidizing bacteria and archaea were correlated with N(nitrogen)contents.However,β-glucosidase activity had no significant correlations with physicochemical properties and metal(loid)contents.Principal components analysis suggested bioavailable Sb and pH were the dominant factors of soil environment in Xikuangshan Sb mining area.Our results can provide a theoretical basis for ecological risk assessment of contaminated soil.
基金supported by the National Natural Science Foundation of China(Nos.41877061,41671308)Central Public-interest Scientific Institution Basal Research Fund(No.BSRF202101)the Agricultural Science and Technology Innovation Program of the Chinese Academy of Agricultural Sciences(No.CAAS-ASTIP-2016-IEDA).
文摘Soil arsenic contamination is of great concern because of its toxicity to human,crops,and soil microorganisms.However,the impacts of arsenic on soil ammonia oxidizers communities remain unclear.Seven types of soil spiked with 0 or 100 mg arsenic per kg soil were incubated for 180 days and sampled at days 1,15,30,90 and 180.The changes in the community composition and abundance of ammonia oxidizing bacteria(AOB)and ammonia oxidizing archaea(AOA)were analyzed by terminal restriction fragment length polymorphism(TRFLP)analysis,clone library sequencing,and quantitative PCR(qPCR)targeting amoA gene.Results revealed considerable variations in the potential ammonia oxidation(PAO)rates in different soils,but soil PAO was not consistently significantly inhibited by arsenic,probably due to the low bioavailable arsenic contents or the existence of functional redundancy between AOB and AOA.The variations in AOB and AOA communities were closely associated with the changes in arsenic fractionations.The amoA gene abundances of AOA increased after arsenic addition,whereas AOB decreased,which corroborated the notion that AOA and AOB might occupy different niches in arsenic-contaminated soils.Phylogenetic analysis of amoA gene-encoded proteins revealed that all AOB clone sequences belonged to the genus Nitrosospira,among which those belonging to Nitrosospira cluster 3a were dominant.The main AOA sequence detected belonged to Thaumarchaeal Group 1.1b,which was considered to have a high ability to adapt to environmental changes.Our results provide new insights into the impacts of arsenic on the soil nitrogen cycling.
基金supported by the National Natural Science Foundation of China(No.52401284)the Natural Science Foundation of Jiangsu Province(No.BK20240957)+1 种基金the Key Research and Development Program of Nantong(No.GZ2024005)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(KYCX25_3677)。
文摘Over recent decades,fuel cell technologies have emerged as viable solutions to address the energy and environmental challenges stemming from fossil fuel dependence.Especially,ammonia has gained increasing attention as an attractive alternative to hydrogen,offering comparable energy density while maintaining carbon-free characteristics,along with superior storage and transport properties that give direct ammonia fuel cells(DAFCs)distinct safety advantages over hydrogen-based systems.Central to this technology is the anodic ammonia oxidation reaction(AOR),where platinum(Pt)remains the most efficient catalyst after years of intensive research.This review offers a comprehensive overview of Ptbased AOR electrocatalysts with potential for application in low-temperature DAFCs.Following an introductory section highlighting key historical developments and catalytic breakthroughs,a fundamental understanding of low-temperature DAFC operation and AOR mechanisms is systematically presented.Subsequently,it outlines the advancements in Pt-based catalysts from simple monometallic systems to sophisticated multimetallic alloys and composites,highlighting material innovations and performance enhancements.Afterward,key challenges and future research directions for advancing AOR electrocatalysts are identified,with the aim of providing valuable guidance for developing practical,highperformance,and low-temperature DAFC systems.
基金National Natural Science Foundation of China,Grant/Award Numbers:22179093,22379111Department of Education of Guangdong Province for Higher Educational Institution,Grant/Award Number:2022ZDZX4104Shenzhen General Project for Institutions of Higher Education,Grant/Award Number:20231127113219001。
文摘Electrochemical nitrogen looping represents a promising carbon-free and sustainable solution for the energy transition,in which electrochemical ammonia oxidation stays at the central position.However,the various nitrogen-containing intermediates tend to poison and corrode the electrocatalysts,even the state-of-the-art noble-metal ones,which is worsened at a high applied potential.Herein,we present an ultrarapid laser quenching strategy for constructing a corrosion-resistant and nanostructured CuNi alloy metallic glass electrocatalyst.In this material,single-atom Cu species are firmly bonded with the surrounding Ni atoms,endowing exceptional resistance against ammonia corrosion relative of conventional CuNi alloys.Remarkably,a record-high durability for over 300 h is achieved.Ultrarapid quenching also allows a much higher Cu content than typical single-atom alloys,simultaneously yielding a high rate and selectivity for ammonia oxidation reaction(AOR).Consequently,an outstanding ammonia conversion rate of up to 95%is achieved with 91.8%selectivity toward nitrite after 8 h.Theoretical simulations reveal that the structural amorphization of CuNi alloy could effectively modify the electronic configuration and reaction pathway,generating stable singleatom Cu active sites with low kinetic barriers for AOR.This ultrarapid laser quenching strategy thus provides a new avenue for constructing metallic glasses with well-defined nanostructures,presenting feasible opportunities for performance enhancement for AOR and other electrocatalytic processes.
基金supported by the grants from the National Key R&D Program of China(Grant No.2019YFA0905500).
文摘Heterotrophic nitrifiers are bacteria that aerobically oxidize ammonia in the presence of organic carbon sources,which differs from autotrophic nitrifiers that extract energy from ammonia oxidation for cell metabolism and growth.The physiological significance of heterotrophic ammonia oxidation remains unclear,even though this process has been known for decades.Here,we demonstrate that direct ammonia oxidation(Dirammox)—a heterotrophic ammonia oxidation process with dinitrogen(N)as the primary product—is associated with both redox balance and the electron transport chain in A/caligenes faecalis.Genetic and proteomic studies indicated that disruption of Dirammox genes(dnfA/dnfB/dnfC)induces a transient redox imbalance and perturbation in energy metabolism,further resulting in delayed growth.In addition,we found via biochemical and physiological studies that endogenous reactive oxygen species(ROS)enhance redox fluxes to ammonia oxidation,and the genetic disruption of cytochrome c peroxidase results in an increased flux of electrons to ammonia oxidation,producing N_(2) and N_(2)O.These unexpected findings provide a more thorough understanding of both the Dirammox process and the physiology of heterotrophic ammonia oxidation.
基金Research Grant Council(Nos.26206115 and 16304117)of the Hong Kong Special Administrative Region.
文摘As a promising fuel candidate,ammonia has been successtully used as anode feed in alkaline fuel cells.However,current technology in catalysts for ammonia electro-oxidation reaction(AOR)with respect to both cost and performance is inadequate to ensure large scale commercial application of direct ammonia fuel cells.Recent studies found that alloying Pt with different transition metals and controlling the morphology of catalysts can improve the AOR activity,and thus potentially can solve the cost issue.Herein,(100)-terminated Pt-M nanocubes(M=3d-transition metals Fe,Co,Ni,Zn)are synthesized via wet-chemistry method and their catalytic activities toward AOR are evaluated.The addition of Fe,Co,Ni and Zn elements can enhance the AOR activity due to decrease in oxophilicity of platinum and bifunctional mechanism.Pt-Zn exhibits the maximum mass activity and specific ativity with values of 0.41 A/mgpt and 169 mA/cm2 that are 1.6 and 1.8 times higher than Pt nanocubes,respectively.Pt-Fe,Pt-Co and PI-Ni nanocubes also ilustrate higher mass and specific activities compared to Pt nanocubes.
基金This work was supported by Westlake Education Foundation.
文摘Electrocatalytic ammonia oxidation reaction(EAOR)provides an ideal solution for on-board hydrogen supply for fuel cells,while the lack of efficient and durable EAOR catalysts has been a long-standing obstacle for its practical application.Herein,we reported that the defect engineering via in-situ electrochemically introducing oxygen vacancies(Vo)not only turns the inactive CuO into efficient EAOR catalyst but also achieves a high stability of over 400 h at a high current density of~200 mA·cm^(−2).Theoretical simulation reveals that the presence of Vo on the CuO surface induces a remarkable upshift of the d-band center of active Cu site closer to the Fermi level,which significantly stabilizes the reaction intermediates(*NHx)and efficiently oxidizes NH3 into N2.This Vo-modulated CuO shows a different catalytic mechanism from that on the conventional Pt-based catalysts,paving a new avenue to develop inexpensive,efficient,and robust catalysts,not limited to EAOR.
基金supported by the National Natural Science Foundation of China(No.22162004)the Natural Science Foundation of Guangxi Province(No.2022JJD120011)the Opening Project of Guangxi Key Laboratory of Information Materials(No.211025-K).
文摘It is still a lack of bifunctional catalysts for ammonia oxidation reaction(AOR)and hydrogen evolution reaction(HER)due to their different reaction mechanisms.In this work,P is doped into PtZn alloy by calcination with NaH_(2)PO_(2) as P source to induce the lattice tensile strain of Pt and the electronic interaction between P and Zn,which optimizes the AOR and HER activity simultaneously.The sample with the optimal P content can drive the AOR peak current density of 293.6 mA·mgPt^(-1),which is almost 2.7 times of Pt.For HER,the overpotential at^(-1)0 mA·cm^(-2) is only 23 mV with Tafel slope of 34.1 mV·dec^(-1).Furthermore,only 0.59 V is needed to obtain 50 mA·mgPt^(-1) for ammonia electrolysis under a two-electrode system.Therefore,this work shows an ingenious method to design bifunctional catalysts for ammonia electrolysis.
基金the National Natural Science Foundation of China(Grant No.51678335)the China Postdoctoral Science Foundation(No.2015M57105).
文摘Ammonia-oxidizing archaeon(AOA)could play important roles for nitrogen removal in the bioreactors under conditions such as low pH and low dissolved oxygen.Therefore,enhancing ammonia oxidation capability of AOA has great significance for water and wastewater treatment,especially under conditions like low dissolved oxygen concentration.Utilizing a novel AOA strain SAT1,which was enriched from a wastewater treatment plant by our group,the effect of magnetic field on AOA’s ammonia oxidation capability,its magnetotaxis and heredity were investigated in this study.Compared with control experiment,AOA’s maximum nitrite-N formation rate during the cultivation increased by 56.8%(0.65 mgN/(L·d))with 20 mT magnetic field.Also,it was testified that AOA possessed a certain magnetotaxis.However,results manifested that the enhancement of AOA’s ammonia oxidation capability was not heritable,that is,lost once the magnetic field was removed.Additionally,the possible mechanism of improving AOA’s ammonia oxidation capability by magnetic field was owing to the promotion of AOA single cells’growth and fission,rather than the enhancement of their ammonia oxidation rates.The results shed light on the application of AOA and methods to enhance AOA’s ammonia oxidation capability,especially in wastewater treatment processes under certain conditions.
基金financially supported by National Natural Science Foundation of China(Grant No.51978007)Research Project of Education Department of Liaoning Province(2020jy009 and 2020jy011).
文摘Measurement and predicted variations of ammonia oxidation rate(AOR)are critical for the optimization of biological nitrogen removal,however,it is difficult to predict accurate AOR based on current models.In this study,a modified model was developed to predict AOR based on laboratoryscale tests and verified through pilot-scale tests.In biological nitrogen removal reactors,the specific ammonia oxidation rate(SAOR)was affected by both mixed liquor volatile suspended solids(MLVSS)concentration and temperature.When MLVSS increased 1.6,4.2,and 7.1-fold(1.3‒8.9 g/L,at 20℃),the measured SAOR decreased by 21%,49%,and 56%,respectively.Thereby,the estimated SAOR was suggested to modify when MLVSS changed through a power equation fitting.In addition,temperature coefficient(θ)was modified based on MLVSS concentration.These results suggested that the prediction of variations ammonia oxidation rate in real wastewater treatment system could be more accurate when considering the effect of MLVSS variations on SAOR.
基金supported by the National Key R&D Program of China(2022YFC3401802)the National Natural Science Foundation of China(22279105)+4 种基金the Zhejiang Provincial Natural Science Foundation(XHD24B0201)the Starting-up Package from Westlake Universitythe Kunpeng Research Fund from Zhejiang ProvinceResearch Center for Industries of the FutureZhejiang Baima Lake Laboratory。
文摘Electrocatalytic ammonia oxidation reaction(eAOR)is of significance to ammonia fuel economy and the production of valuable N-containing products,such as nitrite,nitrate and hydrazine.The study of well-defined molecular catalysts offers rich insights in terms of the detailed mechanism of ammonia oxidation.This review analyzes the thermodynamics of ammonia oxidation reactions and summarizes the current progress in molecular electrocatalysts in this booming field.We emphasized the factors that influence the selectivity of products and further discussed the challenges in designing efficient catalysts.
基金supported by the National Natural Science Foundation of China(22162004,22479031)the Guangxi Science and Technology Program(2023AB38061)+1 种基金the Innovation Project of Guangxi Graduate Education(YCBZ2024053)the Highperformance Computing Platform of Guangxi University。
文摘The oxophilicity of metal oxides is usually utilized to improve the ammonia oxidation reaction(AOR)activity of Pt-based catalysts.But the effect of strong interaction between Pt and metal oxides on AOR is not studied.Herein,experimental and density functional theory calculation results indicate that a strong interaction is built between Pt and reducible CeOx by high-temperature reduction,which induces the electronic interaction due to the difference of work fu nction,then optimizing the competitive adsorption behavior of*OH and*NH_(3)based on hard-soft acid-base principle.Accordingly,the optimal sample achieves an AOR peak current density of 329 mA mg_(Pt)^(-1),which is 2.4 times that of Pt.Meanwhile,it also shows satisfied hydrogen evolution reaction activity with an overpotential of only 24.3 mV at-10 mA cm^(-2)due to the optimization of*H adsorption energy on Pt by CeO_(x).Therefore,this work proposes an AOR activity enhancement mechanism of metal oxides in terms of the strong interaction,and sheds light on developing effective bifunctional catalysts for ammonia electrolysis.
文摘Monte Carlo method is applied to investigate the kinetics of ammonia oxidative decomposition over the commercial propylene ammoxidation catalyst(Mo-Bi). The simulation is quite in agreement with experimental results. Monte Carlo simulation proves that the process of ammonia oxidation decomposition is a two-step reaction.
文摘A range of plant species produce root exudates that inhibit ammonia-oxidizing microorganisms.This biological nitrification inhibition(BNI)capacity can decrease N loss and increase N uptake from the rhizosphere.This study sought evidence for the existence and magnitude of BNI capacity in canola(Brassica napus).Seedlings of three canola cultivars,Brachiaria humidicola(BNI positive)and wheat(Triticum aestivum)were grown in a hydroponic system.Root exudates were collected and their inhibition of the ammonia oxidizing bacterium,Nitrosospira multiformis,was tested.Subsequent pot experiments were used to test the inhibition of native nitrifying communities in soil.Root exudates from canola significantly reduced nitrification rates of both N.multiformis cultures and native soil microbial communities.The level of nitrification inhibition across the three cultivars was similar to the well-studied high-BNI species B.humidicola.BNI capacity of canola may have implications for the N dynamics in farming systems and the N uptake efficiency of crops in rotational farming systems.By reducing nitrification rates canola crops may decrease N losses,increase plant N uptake and encourage microbial N immobilization and subsequently increase the pool of organic N that is available for mineralization during the following cereal crops.
基金supported by the National Natural Science Foundation of China(51978436,52000092,22272116)Fundamental Research Program of Shanxi Province(202103021224043)。
文摘In this work,the CuAl-LDO/c-CNTs catalyst was fabricated via in situ oriented assembly of layered-double hydroxides(LDHs)and citric acid-modified carbon nanotubes(c-CNTs)followed by annealing treatment,and evaluated in the selective catalytic oxidation(SCO)of NH_(3)to N_(2).The CuAl-LDO/c-CNTs catalyst presented better catalytic performance(98%NH_(3)conversion with nearly 90%N_(2)selectivity at 513 K)than other catalysts,such as CuAlO_(x)/CNTs,CuAlO_(x)/c-CNTs and CuAl-LDO/CNTs.Multiple characterizations were utilized to analyze the difference of physicochemical properties among four catalysts.XRD,TEM and XPS analyses manifested that CuO and Cu_(2)O nanoparticles dispersed well on the surface of the Cu Al-LDO/c-CNTs catalyst.Compared with other catalysts,larger specific surface area and better dispersion of CuAl-LDO/c-CNTs catalyst were conducive to the exposure of more active sites,thus improving the redox capacity of the active site and NH_(3)adsorption capacity.In-situ DRIFTS results revealed that the internal selective catalytic reduction(iSCR)mechanism was found over CuAl-LDO/c-CNTs catalyst.
基金financially supported by National Natural Science Foundation of China (No.U20A20130)Fundamental Research Funds for the Central Universities (No.06500152)
文摘Ce1-xZrxO_(2) composite oxides(molar,x=0-1.0,interval of 0.2)were prepared by a cetyltrimethylammonium bromide-assisted precipitation method.The enhancement of silver-species modification and catalytic mechanism of adsorption-transformationdesorption process were investigated over the Ag-impregnated catalysts for lowtemperature selective catalytic oxidation of ammonia(NH_(3)-SCO).The optimal 5 wt.%Ag/Ce_(0.6)Zr_(0.4)O_(2) catalyst presented good NH_(3)-SCO performancewith>90% NH_(3) conversion at temperature(T)≥250°C and 89% N_(2) selectivity.Despite the irregular block shape and underdeveloped specific surface area(∼60m2/g),the naked and Ag-modified Ce_(0.6)Zr_(0.4)O_(2) solid solution still obtained highly dispersed distribution of surface elements analyzed by scanning electron microscope-energy dispersive spectrometer(SEM-EDS)(mapping),N_(2) adsorptiondesorption test and X-ray diffraction(XRD).H2 temperature programmed reduction(H2-TPR)and X-ray photoelectron spectroscopy(XPS)results indicated that Ag-modification enhanced the mobility and activation of oxygen-species leading to a promotion on CeO_(2) reducibility and synergistic Ag0/Ag+and Ce^(4+)/Ce^(3+)redox cycles.Besides,Ag+/Ag_(2)O clusters could facilitate the formation of surface oxygen vacancies that was beneficial to the adsorption and activation of ammonia.NH3-temperature programmed desorption(NH_(3)-TPD)showed more adsorption-desorption capacity to ammoniawere provided by physical,weakandmedium-strong acid sites.Diffused reflectance infrared Fourier transform spectroscopy(DRIFTS)experiments revealed the activation of ammonia might be the control step of NH3-SCO procedure,during which NH3 dehydrogenation derived from NHx-species and also internal selective catalytic reduction(i-SCR)reactions were proposed.
基金Supported by National Natural Science Foundation of China(40532011)~~
文摘[Objective] This study aimed to investigate the abundance and composition of ammonia-oxidizing bacteria and ammonia-oxidizing archaea in Pearl River Estuary sediment.[Method] Firstly,the amoA gene library was constructed;then based on that,the content and diversity of amoA genes of ammonia-oxidizing bacteria and ammonia-oxidizing archaea in Pearl River Estuary sediment were detected by using quantitative real-time polymerase chain reaction（Q-PCR）.[Result] The results of Q-PCR presented that ammonia-oxidizing archaea（AOA） were more abundant than ammonia-oxidizing bacteria（AOB） in the top of sediment cores,with ratios of AOA to AOB of 22 and 9 at the two sites.It suggested that ammonia-oxidizing archaea may play more important roles than ammonia-oxidizing bacteria in the process of ammonia oxidation in the Pearl River Estuary sediment.The phylogenetic tree based on amoA gene sequences revealed that the amoA sequences of both AOA and AOB shared high similarity with the clones from uncultured environment.In the top sediment layer at site Q7,AOB amoA-like gene sequences were dominated by Nitrosomonas-like sequence types,which could be classified into five groups（clusters A,B,C,D and E）.Cluster A accounted for 72.1% of the library.In the top sediment layer,the AOA amoA gene fell into two groups ＂water column/sediment＂ cluster（52.2%） and ＂soil/sediment＂ cluster（47.8%）.But in the bottom sediment layer of Q7,most of the AOA amoA sequences（93.3%） fell into ＂soil/sediment＂ cluster,and a little part（6.7%） fell into the ＂water/sediment＂ cluster.In addition,the total amount of amoA genes in the bottom sediment was higher than that in top sediment.[Conclusion] This study helps to realize the cycle of nitrogen in Pearl River Estuary Region,and thus to provide theoretical support for the treatment of nitrogen eutrophication.
基金supported by the National Natural Science Foundation of China(21403070 and 21373088)Innovation Program of Shanghai Municipal Education Commission(13zz038)+2 种基金Key Project of the Shanghai Committee of Science and Technology(12JC1403600)National Key Technology R&D Program(2012BAE05B02)Shanghai Leading Academic Discipline Project(B409)~~
文摘Small-crystal TS-1 was synthesized via a seed-induced approach using ammonia as the alkali source and tetrapropylammonium bromide as an auxiliary structure-directing agent. The TS-1 samples were characterized using X-ray diffraction, N2 adsorption-desorption, Fourier-transform infrared spectroscopy, inductively coupled plasma atomic emission spectroscopy, scanning electron microscopy, and ultraviolet-visible spectroscopy. The use of the colloidal seed reduced the crystal size, and an appropriate amount of silicalite-1 seed assisted Ti incorporation into the TS-1 framework. This method reduces the cost of TS- 1 synthesis because a significantly smaller amount of tetrapropylammonium hydroxide is used. The catalytic performance of the synthesized small-crystal TS-1 samples in cyclohexanone ammoximation was better than that of bulk TS-1 as a result of improved diffusion and a larger number of active tetrahedral Ti centers.
