Co/NC catalysts modified with rare earth elements(La,Ce,Pr)were prepared by pyrolysis of rare earth elements doped ZIF-67.The experimental results show that the modification of rare earth elements significantly improv...Co/NC catalysts modified with rare earth elements(La,Ce,Pr)were prepared by pyrolysis of rare earth elements doped ZIF-67.The experimental results show that the modification of rare earth elements significantly improves the ammonia decomposition activity and stability of the Co/NC catalyst.The La-Co/NC catalyst can achieve an 82.3%ammonia decomposition and 18.4 mmol hydrogen production rate at 550℃with a GHSV of 20000 cm^(3)·h^(-1).Furthermore,no obvious performance degradation is observed after 72 hours of reaction for all rare earth elements modified catalysts.It is shown that the modification of rare earth elements significantly improves the surface alkalinity and surface chemical state of the catalyst,and thus improves the ammonia decomposition activity of the catalyst.A new type of high-performance ammonia decomposition Co-based catalyst is proposed,and the promoting effect of rare earth elements on the activity of ammonia decomposition is revealed.展开更多
A series of monometallic nitrides and bimetallic nitrides were prepared by temperature-programmed reaction with NH3. The effects of Co, Ni and Fe additives and the synergic action between Fe, Co, Ni and Mo on the amm...A series of monometallic nitrides and bimetallic nitrides were prepared by temperature-programmed reaction with NH3. The effects of Co, Ni and Fe additives and the synergic action between Fe, Co, Ni and Mo on the ammonia decomposition activity were investigated. TPR-MS, XRD were also carried out to obtain better insight into the structure of the bimetallic nitride. The results of ammonia decomposition activity show that bimetallic nitrides are more active than monometallic nitrides or bimetallic oxides.展开更多
Co and Mo bimetallic nitrides supported on Mg（Al）O, MgO and γ-Al2O3 were prepared in temperatureprogrammed reactions with NH3. The surface morphology, chemical composition and catalytic activity for NH3 decompositi...Co and Mo bimetallic nitrides supported on Mg（Al）O, MgO and γ-Al2O3 were prepared in temperatureprogrammed reactions with NH3. The surface morphology, chemical composition and catalytic activity for NH3 decomposition on the supported Co and Mo bimetallic nitrides were studied by X-ray diffractometer （XRD）, NH3 temperature-programmed desorption and mass spectrometer （NH3-TPD-MS）, temperature-programmed desorption and mass spectrometer （TPD-MS）, H2 temperature-programmed surface reaction （H2-TPSR） and activity test. The phases of Co3Mo3N and MoN could be formed on Mg（Al）O, MgO and Al2O3 during the nitridation, and they might be more uniformly dispersed on Mg（Al）O and MgO than on γ-Al2O3. Transition metallic nitrides are generally considered as potential catalysts for hydrogen-involving reactions due to the entrance of hydrogen atoms into subsurface and the lattice of metallic nitrides. The diffusion of nitrogen in the bulk and the structure transformation of Co and Mo nitride compounds occur during NH3-TPD, but the supported Co and Mo bimetallic nitrides are not easily reduced at H2 atmosphere. Co3Mo3N/Mg（Al）O catalyst exhibits the highest activity, while Co3Mo3N/Al2O3 exhibits the lowest activity for NH3 decomposition. Furthermore, the catalytic activity of Co and Mo bimetallic nitrides is not only much higher than that of supported single metallic nitride, but also highly dependent upon the surface acidity and BET surface area of support.展开更多
The influence of preparation conditions （e.g. H2-N2 ratios, final nitriding temperatures） on the performance of MoNx/SBA-15 catalysts for ammonia decomposition was investigated. The variation of catalytic activity w...The influence of preparation conditions （e.g. H2-N2 ratios, final nitriding temperatures） on the performance of MoNx/SBA-15 catalysts for ammonia decomposition was investigated. The variation of catalytic activity with H2-N2 ratios may be attributed to the variation of surface compositions and particle sizes of the active components. The variation of nitriding temperatures leads to the formation of molybdenum nitride domains of varying compositions, which are responsible for the difference in their catalytic performance with respect to ammonia decomposition. At 923 K, ammonia could be completely decomposed using 15800 ml/h·gcat of GHSVNH3, which shows high performance for the catalytic decomposition of ammonia.展开更多
Recently ammonia has been investigated as a fuel for SOFCs （solid oxide fuel cells）. Ammonia is widely produced and transported globally, and stores hydrogen in its bonds making it an excellent fuel for fuel cells. ...Recently ammonia has been investigated as a fuel for SOFCs （solid oxide fuel cells）. Ammonia is widely produced and transported globally, and stores hydrogen in its bonds making it an excellent fuel for fuel cells. The high temperature of SOFCs allows for internal decomposition of ammonia. Previous models of ammonia-fed SOFCs treat ammonia decomposition as having first order dependence on ammonia partial pressure, and ignore the effect of hydrogen inhibition. However, research has shown that at low temperatures （≤ 600 ℃） and low ammonia partial pressures, the rate of ammonia decomposition is inhibited by the presence of hydrogen. This hydrogen inhibition effect was studied and implemented in a model of an ammonia decomposition reactor. Results showed that it may significantly decrease the rate of hydrogen generation. This work sets the foundation for more accurate modelling of intermediate temperature ammonia-fed SOFCs.展开更多
The ammonia decomposition for the production of carbon-free hydrogen has triggered great attention yet still remains challenging due to its sluggish kinetics,posting the importance of precise design of efficient catal...The ammonia decomposition for the production of carbon-free hydrogen has triggered great attention yet still remains challenging due to its sluggish kinetics,posting the importance of precise design of efficient catalysts for ammonia decomposition under low temperatures.Constructing the metal-support interaction and interface is one of the most important strategies for promoting catalysts.In this work,by coating ceria onto the Ni nanoparticles(NPs),we discover that the Ni-CeO_(2)interfaces create an exceptional effect to enhance the catalytic decomposition of ammonia by over 10 folds,compared with the pristine Ni.The kinetic analysis demonstrates that the recombinative N2 desorption is the rate-determining step(RDS)and the Ni-CeO_(2)interface greatly increases the RDS.Based on these understandings,a strategy to fabricate the Ni/CeO_(2)catalyst with abundant Ni-Ce-O interfaces via one-pot sol-gel method was employed(hereafter denoted to s-Ni/CeO_(2)).The s-Ni/CeO_(2)catalyst shows a high activity for ammonia decomposition,achieving a H_(2)formation rate of 10.5 mmol gcat1 min^(-1)at 550℃.Combined with a series of characterizations,the relationship between the catalyst structure and the performance was investigated for further understanding the effect of metal-oxide interfaces.展开更多
Developing high-performance ammonia decomposition catalysts for preparing COx-free hydrogen shows great practical significance.Herein,CeO_(2) is used as a promoter to modulate the metal-support interaction to enhance ...Developing high-performance ammonia decomposition catalysts for preparing COx-free hydrogen shows great practical significance.Herein,CeO_(2) is used as a promoter to modulate the metal-support interaction to enhance the catalytic performance of Ru/Al_(2)O_(3) catalysts.A series of 1Ru/xCe-10AI(x=0.5,1,or 3)catalysts was prepared by a facile colloidal deposition method.We find that the optimized 1 Ru/1Ce-10Al catalyst exhibits excellent activity for the decomposition of ammonia with a very high hydrogen yield of7097 mmolH2/(gRu·min)at 450℃.It is confirmed that Ru species are highly dispersed on the support surface as stable small clusters(~1.3 nm).More importantly,due to the interaction between Ru species and partially reduced CeO_(2-x),the electron density of Ru species is increased,which is beneficial to the high activity of the 1 Ru/xCe-10Al catalysts.This work paves a way to construct high-efficiency ammonia decomposition catalysts modified by CeO_(2).展开更多
In this paper, a series of Fe- and Co-doped lanthanum（hydr）oxides catalysts were prepared by a simple coprecipitationhydrothermal method. The as-prepared catalysts were characterized with various techniques includin...In this paper, a series of Fe- and Co-doped lanthanum（hydr）oxides catalysts were prepared by a simple coprecipitationhydrothermal method. The as-prepared catalysts were characterized with various techniques including powder X-ray diffraction（XRD）, N2 adsorption/desorption, inductively coupled plasma（ICP） and transmission electron microscopy（TEM）. The Fe-based catalysts exhibited consecutive phase changes of amorphous Fe Ox→FeLaO3→Fe2N under different stages（as-prepared→calcination→ammonia decomposition reaction）; as for Co-based catalysts, the phase transformation followed a sequence of Co（OH）2→Co3O4→metallic Co. It was revealed that Fe2N and metallic Co were most probably the active crystalline phase respectively for Feand Co-based catalysts in the decomposition of ammonia.展开更多
Carbon nanotubes （CNTs） supported Co-Mo nitride catalysts were prepared by incipient-wetness impregnation method and temperature-programmed reaction in N2-H2 mixed gases. The effects of cationic promoters （K, Ba, L...Carbon nanotubes （CNTs） supported Co-Mo nitride catalysts were prepared by incipient-wetness impregnation method and temperature-programmed reaction in N2-H2 mixed gases. The effects of cationic promoters （K, Ba, La, Ce and Zr） on the catalytic performance and surface properties were investigated. All samples were characterized by N2 physical adsorption, X-ray diffraction, and temperature-programmed reduction of H2. The results showed that the addition of promoters reduced the crystallite size of Mo2N and Co3Mo3N species and increased their surface area and dispersion. Among the catalysts, the La promoted CoMoNJCNTs catalyst had the highest ammonia conversion which could reach 97.63% at 600 ℃.展开更多
FeCe nanocomposite catalysts with different iron contents were synthesized by a facile co-precipitation method.The as-prepared materials were characterized by various techniques including powder X-ray diffraction(XRD)...FeCe nanocomposite catalysts with different iron contents were synthesized by a facile co-precipitation method.The as-prepared materials were characterized by various techniques including powder X-ray diffraction(XRD),N2 adsorption/desorption and high-resolution transmission electron microscopy(HRTEM).Catalyst with the highest iron content(90 FeCe) shows the best activity for the hydrogen generation via ammonia decomposition.83% NH3 conversion is achieved at 550℃ and nearly full conversion of NH3 is realized at 600℃ with a GHSV of 24000 cm3/(gcat·h).The large content and small size crystal particles of iron species are responsible for the good catalytic performance.Temperatureprogrammed reduction by hydrogen(H2-TPR) was performed to investigate the interaction between cerium and iron species.It is found that slight cerium can exert strong interaction with iron compound thus effectively prevent the self-aggregation of active iron species,so as to improve the catalytic activity for ammonia decomposition.展开更多
Transition metal catalysts have been considerably used for NH3 decomposition because of the potential application in COx-free H2 generation for fuel cells. However, most transition metal catalysts prepared via traditi...Transition metal catalysts have been considerably used for NH3 decomposition because of the potential application in COx-free H2 generation for fuel cells. However, most transition metal catalysts prepared via traditional synthetic approaches performed the inferior stability due to the agglomeration of active components. Here, we adopted an efficient method, aerosol-assisted self- assembly approach （AASA）, to prepare the optimized cobalt-alumina （C0304-A1203） catalysts. The C0304-A1203 catalysts exhibited excellent catalytic performance in the NH3 decomposition reaction, which can reach 100% conversion at 600 ℃and maintain stable for 72 h at a gaseous hourly space velocity （GHSV） of 18000 cm3 gcat-1 h-1. The catalysts were characterized by various techniques including transmission electron microscope （TEM）, scanning electron microscope （SEM）, nitrogen sorption, temperature-programmed reduction by hydrogen （H2-TPR）, ex-situ/in-situ Raman and ex-situ/in-situ X-ray diffraction （XRD） to obtain the information about the structure and property of the catalysts. H2-TPR and in-situ XRD results show that there is strong interaction between the cobalt and alumina species, which influences the redox properties of the catalysts. It is found that even a low content of alumina （10 at%） is able to stabilize the catalysts due to the adequate dispersion and rational interaction between different components, which ensures the high activity and superior stability of the cobalt-alumina catalysts.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
Gasification technology can effectively realize energy recovery from municipal solid waste(MSW)to reduce its negative impact on the environment.However,ammonia,as a pollutant derived from MSW gasification,needs to be ...Gasification technology can effectively realize energy recovery from municipal solid waste(MSW)to reduce its negative impact on the environment.However,ammonia,as a pollutant derived from MSW gasification,needs to be treated because its emission is considered harmful to mankind.This work aims to decompose the NH3 pollutant from MSW gasification by an in-situ catalytic method.The MSW sample is composed of rice,paper,polystyrene granules,rubber gloves,textile and wood chips.Ni–M(M=Co,Fe,Zn)bimetallic catalysts supported on sewage sludge-derived biochar(SSC)were prepared by co-impregnation method and further characterized by X-ray diffraction,N2 isothermal adsorption,scanning electron microscopy,transmission electron microscopy and NH3 temperature programmed desorption.Prior to the experiments,the catalysts were first homogeneously mixed with the MSW sample,and then in-situ catalytic tests were conducted in a horizontal fixed-bed reactor.The effect of the second metal(Co,Fe,Zn)on the catalytic performance was compared to screen the best Ni-M dual.It was found that the Ni–Co/SSC catalyst had the best activity toward NH3 decomposition,whose decomposition rate reached 40.21%at 650℃.The best catalytic performance of Ni–Co/SSC can be explained by its smaller Ni particle size that facilitates the dispersion of active sites as well as the addition of Co reducing the energy barrier for the associative decomposition of NH species during the NH3 decomposition process.Besides,the activity of Ni–Co/SSC increased from 450℃to 700℃as the NH3 decomposition reaction was endothermic.展开更多
Downsizing to sub-nm is a general strategy to reduce the cost of catalysts. However, theoretical Wulff-constructed model suggests that sub-nm clusters show little activity for various reactions such as ammonia decompo...Downsizing to sub-nm is a general strategy to reduce the cost of catalysts. However, theoretical Wulff-constructed model suggests that sub-nm clusters show little activity for various reactions such as ammonia decomposition and ammonia synthesis because of the lack of active sites. As clusters may deviate from the ideal model construction under reaction conditions, a host-guest strategy to synthesize thermally stable 1.0 run monodispersed Ru dusters by the pyrolysis of MIL-101 hosts is reported here to verify the hypothesis. For ammonia decomposition, the activity of the Ru clusters is 25 times higher than that of commercial Ru/active carbon （AC） at full-conversion temperature, while for ammonia synthesis, the activity of the Ru dusters is 500 times as high as that of promoted Ru NPs counterpart. The catalyst also maintains its activities for 40 h without any increase in the size. This model can be used to develop a host-guest strategy for designing thermally stable sub-nm clusters to atomic-efficiently catalyze reactions.展开更多
The novel Ni-Ir/γ-Al2O3 catalyst, denoted as NIA-P, was prepared by high-frequency cold plasma direct reduction method under ambient conditions without thermal treatment, and the conventional sample, denoted as NIA-C...The novel Ni-Ir/γ-Al2O3 catalyst, denoted as NIA-P, was prepared by high-frequency cold plasma direct reduction method under ambient conditions without thermal treatment, and the conventional sample, denoted as NIA-CR, was prepared by impregnation, thermal calcination, and then by H2 reduction method. The effects of reduction methods on the catalysts for ammonia decomposition were studied, and they were characterized by XRD, N2 adsorption, XPS, and H2-TPD. It was found that the plasma-reduced NIA-P sample showed a better catalytic performance, over which ammonia conversion was 68.9%, at T = 450℃, P = 1 atm, and GHSV = 30, 000 h^-1. It was 31.7% higher than that of the conventional NIA-CR sample. XRD results showed that the crystallite size decreased for the sample with plasma reduction, and the dispersion of active components was improved. There were more active components on the surface of the NIA-P sample from the XPS results. This effect resulted in the higher activity for decomposition of ammonia. Meanwhile, the plasma process significantly decreased the time of preparing catalyst.展开更多
Effects of carrier gas composition（N2/air） on NH3 production, energy efficiency regarding NH3 production and byproducts formation from plasma-catalytic decomposition of urea were systematically investigated using an...Effects of carrier gas composition（N2/air） on NH3 production, energy efficiency regarding NH3 production and byproducts formation from plasma-catalytic decomposition of urea were systematically investigated using an Al2 O3-packed dielectric barrier discharge（DBD） reactor at room temperature. Results show that the presence of O2 in the carrier gas accelerates the conversion of urea but leads to less generation of NH3. The final yield of NH3 in the gas phase decreased from 70.5%, 78.7%, 66.6% and 67.2% to 54.1%, 51.7%, 49.6% and 53.4% for applied voltages of 17, 19, 21 and 23 kV, respectively when air was used as the carrier gas instead of N2.From the viewpoint of energy savings, however, air carrier gas is better than N2 due to reduced energy consumption and increased energy efficiency for decomposition of a fixed amount of urea. Carrier gas composition has little influence on the major decomposition pathways of urea under the synergetic effects of plasma and Al2 O3 catalyst to give NH3 and CO2 as the main products. Compared to a small amount of N2 O formed with N2 as the carrier gas, however,more byproducts including N2O and NO2 in the gas phase and NH4 NO3 in solid deposits were produced with air as the carrier gas, probably due to the unproductive consumption of NH3, the possible intermediate HNCO and even urea by the abundant active oxygen species and nitrogen oxides generated in air-DBD plasma.展开更多
Catalytic decomposition of NH3 to high purity hydrogen offers a promising strategy for fuel cells, but presents challenges for high hydrogen yields at comparatively low temperatures due to the lack of efficient cataly...Catalytic decomposition of NH3 to high purity hydrogen offers a promising strategy for fuel cells, but presents challenges for high hydrogen yields at comparatively low temperatures due to the lack of efficient catalysts. Here, we report the facile preparation of ultra-fine ruthenium（Ru） species dispersed on Mg O, which show excellent activity and high temperature stability for NH3 decomposition reaction. The hydrogen yield of the prepared Ru/Mg O catalysts reaches ca. 2,092 mmol H2 g–1 Ru min–1 at450 °C, far exceeding that of the previously reported most reactive Ru-based catalysts and the same chemical composition samples prepared by other approaches. Various characterization techniques containing X-ray absorption fine structure（XAFS）,in-situ diffuse reflectance infrared Fourier transform spectroscopy（in-situ DRTFTS） and temperature-programmed reduction/desorption（TPR/TPD） were carried out to explore the structure-function relation of the prepared Ru/Mg O catalysts. We found that the Ru species interact strongly with the Mg O support, which can efficiently protect the Ru species and Mg O support from agglomerating during NH3 decomposition test, maintaining the stability of the catalysts.展开更多
The catalytic performance is highly related to the catalyst structure.Herein,a series of Ni nanoparticles supported on Y_(2)O_(3) with different morphologies were successfully synthesized via hydrothermal process scre...The catalytic performance is highly related to the catalyst structure.Herein,a series of Ni nanoparticles supported on Y_(2)O_(3) with different morphologies were successfully synthesized via hydrothermal process screening different pH environments.These Ni/Y_(2)O_(3)catalysts were applied to efficiently produce CO_(x)-free H2through ammonia decomposition.We identify a significant impact of Y_(2)O_(3)supports on nickel nanoclusters sizes and dispersion.The experimental results show that Ni/Y11 catalyst achieves 100% ammonia decomposition conversion under a gas hour space velocity(GHSV) of 12,000 ml·h^(-1)·gcat^(-1) and temperature of 650℃.Such a high level of activity over Ni/Y11 catalyst was attributed to a large specific surface area,appropriate alkalinity,and small Ni nanoparticles diameter with high dispersion.展开更多
We report an in-depth study of catalytic N–H bond dissociation with typical platinum clusters on gra-phene supports.Among all the pristine graphene-and defective graphene-supported Pt clusters of different sizes that...We report an in-depth study of catalytic N–H bond dissociation with typical platinum clusters on gra-phene supports.Among all the pristine graphene-and defective graphene-supported Pt clusters of different sizes that were studied,the Pt_(3)/G cluster possesses the highest reactivity and lowest activa-tion barriers for each step of N–H dissociation in the decomposition of ammonia.展开更多
基金Funded in part by the Natural Science Foundation of China(No.22279096)the Guangdong Basic and Applied Basic Research Foundation(No.2021B1515120072)。
文摘Co/NC catalysts modified with rare earth elements(La,Ce,Pr)were prepared by pyrolysis of rare earth elements doped ZIF-67.The experimental results show that the modification of rare earth elements significantly improves the ammonia decomposition activity and stability of the Co/NC catalyst.The La-Co/NC catalyst can achieve an 82.3%ammonia decomposition and 18.4 mmol hydrogen production rate at 550℃with a GHSV of 20000 cm^(3)·h^(-1).Furthermore,no obvious performance degradation is observed after 72 hours of reaction for all rare earth elements modified catalysts.It is shown that the modification of rare earth elements significantly improves the surface alkalinity and surface chemical state of the catalyst,and thus improves the ammonia decomposition activity of the catalyst.A new type of high-performance ammonia decomposition Co-based catalyst is proposed,and the promoting effect of rare earth elements on the activity of ammonia decomposition is revealed.
文摘A series of monometallic nitrides and bimetallic nitrides were prepared by temperature-programmed reaction with NH3. The effects of Co, Ni and Fe additives and the synergic action between Fe, Co, Ni and Mo on the ammonia decomposition activity were investigated. TPR-MS, XRD were also carried out to obtain better insight into the structure of the bimetallic nitride. The results of ammonia decomposition activity show that bimetallic nitrides are more active than monometallic nitrides or bimetallic oxides.
文摘Co and Mo bimetallic nitrides supported on Mg（Al）O, MgO and γ-Al2O3 were prepared in temperatureprogrammed reactions with NH3. The surface morphology, chemical composition and catalytic activity for NH3 decomposition on the supported Co and Mo bimetallic nitrides were studied by X-ray diffractometer （XRD）, NH3 temperature-programmed desorption and mass spectrometer （NH3-TPD-MS）, temperature-programmed desorption and mass spectrometer （TPD-MS）, H2 temperature-programmed surface reaction （H2-TPSR） and activity test. The phases of Co3Mo3N and MoN could be formed on Mg（Al）O, MgO and Al2O3 during the nitridation, and they might be more uniformly dispersed on Mg（Al）O and MgO than on γ-Al2O3. Transition metallic nitrides are generally considered as potential catalysts for hydrogen-involving reactions due to the entrance of hydrogen atoms into subsurface and the lattice of metallic nitrides. The diffusion of nitrogen in the bulk and the structure transformation of Co and Mo nitride compounds occur during NH3-TPD, but the supported Co and Mo bimetallic nitrides are not easily reduced at H2 atmosphere. Co3Mo3N/Mg（Al）O catalyst exhibits the highest activity, while Co3Mo3N/Al2O3 exhibits the lowest activity for NH3 decomposition. Furthermore, the catalytic activity of Co and Mo bimetallic nitrides is not only much higher than that of supported single metallic nitride, but also highly dependent upon the surface acidity and BET surface area of support.
文摘The influence of preparation conditions （e.g. H2-N2 ratios, final nitriding temperatures） on the performance of MoNx/SBA-15 catalysts for ammonia decomposition was investigated. The variation of catalytic activity with H2-N2 ratios may be attributed to the variation of surface compositions and particle sizes of the active components. The variation of nitriding temperatures leads to the formation of molybdenum nitride domains of varying compositions, which are responsible for the difference in their catalytic performance with respect to ammonia decomposition. At 923 K, ammonia could be completely decomposed using 15800 ml/h·gcat of GHSVNH3, which shows high performance for the catalytic decomposition of ammonia.
文摘Recently ammonia has been investigated as a fuel for SOFCs （solid oxide fuel cells）. Ammonia is widely produced and transported globally, and stores hydrogen in its bonds making it an excellent fuel for fuel cells. The high temperature of SOFCs allows for internal decomposition of ammonia. Previous models of ammonia-fed SOFCs treat ammonia decomposition as having first order dependence on ammonia partial pressure, and ignore the effect of hydrogen inhibition. However, research has shown that at low temperatures （≤ 600 ℃） and low ammonia partial pressures, the rate of ammonia decomposition is inhibited by the presence of hydrogen. This hydrogen inhibition effect was studied and implemented in a model of an ammonia decomposition reactor. Results showed that it may significantly decrease the rate of hydrogen generation. This work sets the foundation for more accurate modelling of intermediate temperature ammonia-fed SOFCs.
基金supported by the National Key R&D Program of China(No.2022YFB4002401,2022YFB4003701)the National Natural Science Foundation of China(Nos.22178058,22308055)+2 种基金Science Fund for Creative Research Groups of the National Natural Science Foundation of China(22221005)Natural Science Foundation of Fujian Province(2022J05027)the Talent Program of Fuzhou University(XRC-22036).
文摘The ammonia decomposition for the production of carbon-free hydrogen has triggered great attention yet still remains challenging due to its sluggish kinetics,posting the importance of precise design of efficient catalysts for ammonia decomposition under low temperatures.Constructing the metal-support interaction and interface is one of the most important strategies for promoting catalysts.In this work,by coating ceria onto the Ni nanoparticles(NPs),we discover that the Ni-CeO_(2)interfaces create an exceptional effect to enhance the catalytic decomposition of ammonia by over 10 folds,compared with the pristine Ni.The kinetic analysis demonstrates that the recombinative N2 desorption is the rate-determining step(RDS)and the Ni-CeO_(2)interface greatly increases the RDS.Based on these understandings,a strategy to fabricate the Ni/CeO_(2)catalyst with abundant Ni-Ce-O interfaces via one-pot sol-gel method was employed(hereafter denoted to s-Ni/CeO_(2)).The s-Ni/CeO_(2)catalyst shows a high activity for ammonia decomposition,achieving a H_(2)formation rate of 10.5 mmol gcat1 min^(-1)at 550℃.Combined with a series of characterizations,the relationship between the catalyst structure and the performance was investigated for further understanding the effect of metal-oxide interfaces.
基金Project supported by the National Key Basic Research Program of China(2021YFA1501103)the National Science Fund for Distinguished Young Scholars of China(22225110)+1 种基金the National Natural Science Foundation of China(22075166,22271177)the Taishan Scholar Project of Shandong Province of China,and the Young Scholars Program of Shandong University.
文摘Developing high-performance ammonia decomposition catalysts for preparing COx-free hydrogen shows great practical significance.Herein,CeO_(2) is used as a promoter to modulate the metal-support interaction to enhance the catalytic performance of Ru/Al_(2)O_(3) catalysts.A series of 1Ru/xCe-10AI(x=0.5,1,or 3)catalysts was prepared by a facile colloidal deposition method.We find that the optimized 1 Ru/1Ce-10Al catalyst exhibits excellent activity for the decomposition of ammonia with a very high hydrogen yield of7097 mmolH2/(gRu·min)at 450℃.It is confirmed that Ru species are highly dispersed on the support surface as stable small clusters(~1.3 nm).More importantly,due to the interaction between Ru species and partially reduced CeO_(2-x),the electron density of Ru species is increased,which is beneficial to the high activity of the 1 Ru/xCe-10Al catalysts.This work paves a way to construct high-efficiency ammonia decomposition catalysts modified by CeO_(2).
基金Project supported by the National Natural Science Foundation of China(21301107,21501109)Fundamental Research Funding of Shandong University(2014JC005)+1 种基金the Taishan Scholar Project of Shandong Province(China)Doctoral Funding of Ministry of Education of China(20130131120009)
文摘In this paper, a series of Fe- and Co-doped lanthanum（hydr）oxides catalysts were prepared by a simple coprecipitationhydrothermal method. The as-prepared catalysts were characterized with various techniques including powder X-ray diffraction（XRD）, N2 adsorption/desorption, inductively coupled plasma（ICP） and transmission electron microscopy（TEM）. The Fe-based catalysts exhibited consecutive phase changes of amorphous Fe Ox→FeLaO3→Fe2N under different stages（as-prepared→calcination→ammonia decomposition reaction）; as for Co-based catalysts, the phase transformation followed a sequence of Co（OH）2→Co3O4→metallic Co. It was revealed that Fe2N and metallic Co were most probably the active crystalline phase respectively for Feand Co-based catalysts in the decomposition of ammonia.
基金Project supported by National Natural Science Foundation of China (20806017)Natural Science Foundation of Guangdong Province (10151009101000009)
文摘Carbon nanotubes （CNTs） supported Co-Mo nitride catalysts were prepared by incipient-wetness impregnation method and temperature-programmed reaction in N2-H2 mixed gases. The effects of cationic promoters （K, Ba, La, Ce and Zr） on the catalytic performance and surface properties were investigated. All samples were characterized by N2 physical adsorption, X-ray diffraction, and temperature-programmed reduction of H2. The results showed that the addition of promoters reduced the crystallite size of Mo2N and Co3Mo3N species and increased their surface area and dispersion. Among the catalysts, the La promoted CoMoNJCNTs catalyst had the highest ammonia conversion which could reach 97.63% at 600 ℃.
基金Project supported by the Natural Science Foundation of Jiangsu Province (BK20170232,BK20170238)National Natural Science Foundation of China (51908256)。
文摘FeCe nanocomposite catalysts with different iron contents were synthesized by a facile co-precipitation method.The as-prepared materials were characterized by various techniques including powder X-ray diffraction(XRD),N2 adsorption/desorption and high-resolution transmission electron microscopy(HRTEM).Catalyst with the highest iron content(90 FeCe) shows the best activity for the hydrogen generation via ammonia decomposition.83% NH3 conversion is achieved at 550℃ and nearly full conversion of NH3 is realized at 600℃ with a GHSV of 24000 cm3/(gcat·h).The large content and small size crystal particles of iron species are responsible for the good catalytic performance.Temperatureprogrammed reduction by hydrogen(H2-TPR) was performed to investigate the interaction between cerium and iron species.It is found that slight cerium can exert strong interaction with iron compound thus effectively prevent the self-aggregation of active iron species,so as to improve the catalytic activity for ammonia decomposition.
基金supported by the National Natural Science Foundation of China (21622106, 21501109, 21771117)the Outstanding Scholar Fund from the Science Foundation of Shandong Province of China (JQ201703)the Taishan Scholar Project of Shandong Province of China
文摘Transition metal catalysts have been considerably used for NH3 decomposition because of the potential application in COx-free H2 generation for fuel cells. However, most transition metal catalysts prepared via traditional synthetic approaches performed the inferior stability due to the agglomeration of active components. Here, we adopted an efficient method, aerosol-assisted self- assembly approach （AASA）, to prepare the optimized cobalt-alumina （C0304-A1203） catalysts. The C0304-A1203 catalysts exhibited excellent catalytic performance in the NH3 decomposition reaction, which can reach 100% conversion at 600 ℃and maintain stable for 72 h at a gaseous hourly space velocity （GHSV） of 18000 cm3 gcat-1 h-1. The catalysts were characterized by various techniques including transmission electron microscope （TEM）, scanning electron microscope （SEM）, nitrogen sorption, temperature-programmed reduction by hydrogen （H2-TPR）, ex-situ/in-situ Raman and ex-situ/in-situ X-ray diffraction （XRD） to obtain the information about the structure and property of the catalysts. H2-TPR and in-situ XRD results show that there is strong interaction between the cobalt and alumina species, which influences the redox properties of the catalysts. It is found that even a low content of alumina （10 at%） is able to stabilize the catalysts due to the adequate dispersion and rational interaction between different components, which ensures the high activity and superior stability of the cobalt-alumina catalysts.
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.
基金supported by the National Key R&D Program of China(No.2019YFC1906803)Key R&D Program of Jiangsu Province(No.BE2021701).
文摘Gasification technology can effectively realize energy recovery from municipal solid waste(MSW)to reduce its negative impact on the environment.However,ammonia,as a pollutant derived from MSW gasification,needs to be treated because its emission is considered harmful to mankind.This work aims to decompose the NH3 pollutant from MSW gasification by an in-situ catalytic method.The MSW sample is composed of rice,paper,polystyrene granules,rubber gloves,textile and wood chips.Ni–M(M=Co,Fe,Zn)bimetallic catalysts supported on sewage sludge-derived biochar(SSC)were prepared by co-impregnation method and further characterized by X-ray diffraction,N2 isothermal adsorption,scanning electron microscopy,transmission electron microscopy and NH3 temperature programmed desorption.Prior to the experiments,the catalysts were first homogeneously mixed with the MSW sample,and then in-situ catalytic tests were conducted in a horizontal fixed-bed reactor.The effect of the second metal(Co,Fe,Zn)on the catalytic performance was compared to screen the best Ni-M dual.It was found that the Ni–Co/SSC catalyst had the best activity toward NH3 decomposition,whose decomposition rate reached 40.21%at 650℃.The best catalytic performance of Ni–Co/SSC can be explained by its smaller Ni particle size that facilitates the dispersion of active sites as well as the addition of Co reducing the energy barrier for the associative decomposition of NH species during the NH3 decomposition process.Besides,the activity of Ni–Co/SSC increased from 450℃to 700℃as the NH3 decomposition reaction was endothermic.
文摘Downsizing to sub-nm is a general strategy to reduce the cost of catalysts. However, theoretical Wulff-constructed model suggests that sub-nm clusters show little activity for various reactions such as ammonia decomposition and ammonia synthesis because of the lack of active sites. As clusters may deviate from the ideal model construction under reaction conditions, a host-guest strategy to synthesize thermally stable 1.0 run monodispersed Ru dusters by the pyrolysis of MIL-101 hosts is reported here to verify the hypothesis. For ammonia decomposition, the activity of the Ru clusters is 25 times higher than that of commercial Ru/active carbon （AC） at full-conversion temperature, while for ammonia synthesis, the activity of the Ru dusters is 500 times as high as that of promoted Ru NPs counterpart. The catalyst also maintains its activities for 40 h without any increase in the size. This model can be used to develop a host-guest strategy for designing thermally stable sub-nm clusters to atomic-efficiently catalyze reactions.
基金National Natural Science Foundation of China (20590360)New Century Excellent Talent Project of China (NCET-05-0783)
文摘The novel Ni-Ir/γ-Al2O3 catalyst, denoted as NIA-P, was prepared by high-frequency cold plasma direct reduction method under ambient conditions without thermal treatment, and the conventional sample, denoted as NIA-CR, was prepared by impregnation, thermal calcination, and then by H2 reduction method. The effects of reduction methods on the catalysts for ammonia decomposition were studied, and they were characterized by XRD, N2 adsorption, XPS, and H2-TPD. It was found that the plasma-reduced NIA-P sample showed a better catalytic performance, over which ammonia conversion was 68.9%, at T = 450℃, P = 1 atm, and GHSV = 30, 000 h^-1. It was 31.7% higher than that of the conventional NIA-CR sample. XRD results showed that the crystallite size decreased for the sample with plasma reduction, and the dispersion of active components was improved. There were more active components on the surface of the NIA-P sample from the XPS results. This effect resulted in the higher activity for decomposition of ammonia. Meanwhile, the plasma process significantly decreased the time of preparing catalyst.
基金supported by the National Natural Science Foundation of China (Nos. 21547004, 51638001)the Beijing Natural Science Foundation (No. 8152011)the Scientific Research Program of Beijing Municipal Education Commission (No. KM201510005009)
文摘Effects of carrier gas composition（N2/air） on NH3 production, energy efficiency regarding NH3 production and byproducts formation from plasma-catalytic decomposition of urea were systematically investigated using an Al2 O3-packed dielectric barrier discharge（DBD） reactor at room temperature. Results show that the presence of O2 in the carrier gas accelerates the conversion of urea but leads to less generation of NH3. The final yield of NH3 in the gas phase decreased from 70.5%, 78.7%, 66.6% and 67.2% to 54.1%, 51.7%, 49.6% and 53.4% for applied voltages of 17, 19, 21 and 23 kV, respectively when air was used as the carrier gas instead of N2.From the viewpoint of energy savings, however, air carrier gas is better than N2 due to reduced energy consumption and increased energy efficiency for decomposition of a fixed amount of urea. Carrier gas composition has little influence on the major decomposition pathways of urea under the synergetic effects of plasma and Al2 O3 catalyst to give NH3 and CO2 as the main products. Compared to a small amount of N2 O formed with N2 as the carrier gas, however,more byproducts including N2O and NO2 in the gas phase and NH4 NO3 in solid deposits were produced with air as the carrier gas, probably due to the unproductive consumption of NH3, the possible intermediate HNCO and even urea by the abundant active oxygen species and nitrogen oxides generated in air-DBD plasma.
基金supported by the Excellent Young Scientists Fund from National Natural Science Foundation of China (21622106)other projects from the National Natural Science Foundation of China (21773288, 21805167, 11574281, 21771117)+5 种基金the Outstanding Scholar Fund (JQ201703)the Doctoral Fund (ZR2018BB010)the Science Foundation of Shandong Province of Chinathe Taishan Scholar Project of Shandong Province of Chinathe National Key Basic Research Program of China (2017YFA0403402)the Future Program for Young Scholar of Shandong University
文摘Catalytic decomposition of NH3 to high purity hydrogen offers a promising strategy for fuel cells, but presents challenges for high hydrogen yields at comparatively low temperatures due to the lack of efficient catalysts. Here, we report the facile preparation of ultra-fine ruthenium（Ru） species dispersed on Mg O, which show excellent activity and high temperature stability for NH3 decomposition reaction. The hydrogen yield of the prepared Ru/Mg O catalysts reaches ca. 2,092 mmol H2 g–1 Ru min–1 at450 °C, far exceeding that of the previously reported most reactive Ru-based catalysts and the same chemical composition samples prepared by other approaches. Various characterization techniques containing X-ray absorption fine structure（XAFS）,in-situ diffuse reflectance infrared Fourier transform spectroscopy（in-situ DRTFTS） and temperature-programmed reduction/desorption（TPR/TPD） were carried out to explore the structure-function relation of the prepared Ru/Mg O catalysts. We found that the Ru species interact strongly with the Mg O support, which can efficiently protect the Ru species and Mg O support from agglomerating during NH3 decomposition test, maintaining the stability of the catalysts.
基金financially supported by the National Natural Science Foundation of China (Nos.21868016, 21763018,22005296 and 21875096)the Key Laboratory for Environment and Energy Catalysis of Jiangxi Province (No. 20181BCD40004)+1 种基金the Natural Science Foundation of Jiangxi Province (No.20181BAB203016)the Graduate Students Innovation Special Foundation of Jiangxi Province (No.YC2021-B014)。
文摘The catalytic performance is highly related to the catalyst structure.Herein,a series of Ni nanoparticles supported on Y_(2)O_(3) with different morphologies were successfully synthesized via hydrothermal process screening different pH environments.These Ni/Y_(2)O_(3)catalysts were applied to efficiently produce CO_(x)-free H2through ammonia decomposition.We identify a significant impact of Y_(2)O_(3)supports on nickel nanoclusters sizes and dispersion.The experimental results show that Ni/Y11 catalyst achieves 100% ammonia decomposition conversion under a gas hour space velocity(GHSV) of 12,000 ml·h^(-1)·gcat^(-1) and temperature of 650℃.Such a high level of activity over Ni/Y11 catalyst was attributed to a large specific surface area,appropriate alkalinity,and small Ni nanoparticles diameter with high dispersion.
基金This work was supported financially by the National Natural Science Foundation of China(grant nos.21722308 and 21802146)CAS Key Research Project of Frontier Science(CAS Grant QYZDB-SSW-SLH024)Frontier Cross Project of the National Laboratory for Molecular Sciences(051Z011BZ3).
文摘We report an in-depth study of catalytic N–H bond dissociation with typical platinum clusters on gra-phene supports.Among all the pristine graphene-and defective graphene-supported Pt clusters of different sizes that were studied,the Pt_(3)/G cluster possesses the highest reactivity and lowest activa-tion barriers for each step of N–H dissociation in the decomposition of ammonia.
