Ammonia Decomposition over Bimetallic Nitrides Supported on g-Al_2O_3

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.

CeO_(2-x) modified Ru/γ-Al_(2)O_(3) catalysts for ammonia decomposition reaction

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).

Fe- and Co-doped lanthanum oxides catalysts for ammonia decomposition:Structure and catalytic performances

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.

Effect of rare earth and other cationic promoters on properties of CoMoN_x/CNTs catalysts for ammonia decomposition

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 ℃.

FeCe nanocomposite with high iron content as efficient catalyst for generation of COx-free hydrogen via ammonia decomposition

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.

In-situ catalytic decomposition of emitted ammonia from municipal solid waste gasification by Ni–M bimetallic catalysts supported on sewage sludge-derived biochar

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.

Sub-nm ruthenium cluster catalyst for decomposition as an efficient and robust and synthesis of ammonia： Break the ＂size shackles＂

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.

Preparation of novel Ni-Ir/γ-Al_2O_3 catalyst via high-frequency cold plasma direct reduction process

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.

Production of ammonia from plasma-catalytic decomposition of urea: Effects of carrier gas composition

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.

Hydrogen production via catalytic decomposition of NH3 using promoted MgO-supported ruthenium catalysts

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 MgO,which show excellent activity and high temperature stability for NH3 decomposition reaction.The hydrogen yield of the prepared Ru/MgO catalysts reaches ca.2,092 mmol H2 gRu^-1 min^-1 at 450℃,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/MgO catalysts.We found that the Ru species interact strongly with the MgO support,which can efficiently protect the Ru species and MgO support from agglomerating during NH3 decomposition test,maintaining the stability of the catalysts.

Engineering morphologies of yttrium oxide supported nickel catalysts for hydrogen production

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.

Enhanced Catalysis of Pt_(3) Clusters Supported on Graphene for N–H Bond Dissociation

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.