Adsorption microcalorimetric studies of the interaction between oxygen and an industrial ammonia synthesis catalyst

Heats of oxygen adsorption on an industrial Ca-IB type catalyst for ammonia synthesis have been measured at 20°C. Participation of various forms of adsorbed oxygen (adsorption heats of 420 kJ/mol and below 84 kJ/mol) in the formation of a passivating (stabilizing) catalyst layer has been found.

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CA-IB 20°C. ( 100 / 20 /) () .

     

Mechanism of oxygen poisoning of ammonia synthesis catalyst

The effect of oxygen adsorbed on the surface of a commercial catalyst from a mixture of hydrogen with water vapor on the steady-state and nonsteady-state ammonia synthesis kinetics is studied under gradientless conditions at the pressures of the stoichiometric nitrogen-hydrogen mixture below the atmospheric pressure and at the temperatures of 285 and 240°C. The results obtained are discussed on the basis of the concepts of the ammonia synthesis theory of Temkin. The poisoning effect of oxygen on the reaction rate is explained by an increase in the activation energy of the rate constant k ₊ in the Temkin-Pyzhev equation, i.e., an increase in the activation energy of the rate constant of nitrogen adsorption at the fixed nitrogen adsorption heat. This conclusion agrees with the concepts of Ertl et al., according to which the activation energy of nitrogen adsorption on iron changes in symbasis with the variation of the electronic work function. Oxygen adsorption on the catalyst surface increases the electronic work function. Thus, the mechanism of the catalyst poisoning by oxygen (at its low surface coverage) consists in an increase in the electronic work function. Assumptions are stated as to the role of chemical promoters of iron catalysts.     

The surface properties of iron catalyst for ammonia synthesis

The reduction process and the surface properties of industrial prereduced triply and doubly promoted iron catalyst for ammonia synthesis have been studied using thermogravimetry, thermal desorption of N₂ and X-ray diffraction. The properties of both catalysts have been discussed on the basis of the double layer model of iron catalyst. A concept of facet formation on the active surface of the catalysts has been proposed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Interaction between catalysts for ammonia synthesis and oxygen

Reversible poisoning of the catalysts for ammonia synthesis by oxygen has been used to eliminate the pyrophoric nature of the reduced catalysts via their treatment by the mixtures of nitrogen, hydrogen or helium with oxygen at catalysis temperatures. Kinetic studies of oxygen sorption, catalyst structure, activity and stability to the secondary oxidation of the samples partially oxidized at various temperatures have revealed that the optimum temperatures to eliminate the pyrophoric effect are 673–773 K.

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, . , , , 673–773 K.

     

Kinetics of reduction of an iron catalyst for ammonia synthesis

The kinetics of reduction of an iron catalyst have been studied at 450–550 °C. The overall kinetic equation was of the mixed-control type. The equation of the surface reaction was of the Langmuir-Hinshelwood type with the adsorption of only water vapor taken into account.

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450–550°C. . - .

     

Ammonia-treated activated carbon as support of Ru-Ba catalyst for ammonia synthesis

Ammonia-treated activated carbon has been studied as a support of Ru-Ba catalyst for ammonia synthesis. It is shown that the introduction of nitrogen leads to a decrease of ammonia synthesis activity for the catalysts with a low Ba/Ru molar ratio, while no significant changes are obtained for the catalysts with a high Ba/Ru molar ratio, confirming that electronegative impurities suppress the activity in ammonia synthesis and consume part of the promoters. This revised version was published online in June 2006 with corrections to the Cover Date.     

Scanning electron microscopic study of an industrial catalyst for ammonia synthesis

The surface topography and elemental composition of the near-surface layers of a reduced passivated catalyst for ammonia synthesis have been studied on a scanning electron microscope in the initial state and after high-temperature oxygen treatment as well as removal of the alkali promoter.

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CA-IB , .

     

New efficient catalyst for ammonia synthesis: barium-promoted cobalt on carbon

Barium-promoted cobalt catalysts supported on carbon exhibit higher ammonia activities at synthesis temperatures than the commercial, multipromoted iron catalyst and also a lower ammonia inhibition.     

Single atom catalyst towards ammonia synthesis at mild conditions

正Nitrogen is an essential nutrient element for all living organisms,however in its sufficient molecular form,nitrogen could not be utilized to meet the crucial need for global food requirements or industrial production due to its strong nonpolar N≡N triple bond.Therefore,nitrogen fixation is an essential transformation but this only occurs in the nature with the help of nitrogenases[1].Although nitrogen can be artificially transformed into ammonia through the wellestablished Haber-Bosch process,the reaction is accomplished under drastic conditions,such as high temperature     

Zn nanosheets:An earth-abundant metallic catalyst for efficient electrochemical ammonia synthesis

Ammonia(NH₃),a critical raw material for various industrial chemicals,is also recognized as a clean and efficient energy carrier for the future energy economy[1].However,the industrial-scale production of NH₃ strongly relies on the Haber-Bosch process,which involves massive fuel consumption and enormous greenhouse gas emissions[2].Therefore,there is an urgent need to develop sustainable and energy-saving alternative routes for artificial NH3 production.     

非晶Fe~90Zr~10合金氨合成催化剂的活化行为

在氨合成气氨中对非晶Fe~90Zr~10合金条带进行了活化。采用AES, XPS, SAM,SEM等分析方法, 并结合氩离子原位轰击剥层研究了非晶Fe~90Zr~10合金条带活化前后自由侧及贴辊侧的表层成分分布, 元素化学状态及表面形貌, 结果表明, 原始条带自由侧表层存在差显著的Zr偏聚, 而贴辊侧表层则存在着Fe的偏聚和Zr的贫集。贴辊侧和自由侧表面Fe氧化物分别为Fe~3O~4和Fe~2O~3。活化后, 自由侧表面Zr浓度下降,而贴辊侧表面Zr浓度增加, 贴辊侧Fe氧化物得到了全部还原, 活化后条带体结构发生了晶化, 表面形成了蜂窝状结构及许多环状裂纹, 对活化机理进行了讨论。     

Some features of the ammonia synthesis mechanism on an iron catalyst

Russian Chemical Bulletin - The features of the ammonia synthesis mechanism on an iron catalyst were studied, making it possible to clarify the hydrogen role in the step of the molecular nitrogen...     

SEM-EDAX investigations of use-related microstructural changes in an ammonia synthesis catalyst

Changes in the topography and distribution of the chemical constituents in the microspaces of oxide type catalysts and prereduced catalysts have been investigated by scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDAX) before and after six years of use in industrial ammonia synthesis reactors.

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6- .

     

Novel preparation of nanocrystalline magnesia-supported caesium-promoted ruthenium catalyst with high activity for ammonia synthesis

A caesium-promoted ruthenium catalyst supported on nanocrystalline magnesia with high activity for ammonia synthesis was conveniently prepared by using hydrated ruthenium trichloride and hexahydrate magnesium nitrate as precursors, whereas dechlorination post-treatment and ready-made magnesia were not necessary.