Fused Catalysts

Schlögl, Robert

doi:10.1002/9783527610044.hetcat0006

Cited by 2 publications

(1 citation statement)

References 61 publications

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“…The quasi-equilibrated reactions steps from N ads to NH 3 are highly endothermic. [41] Therefore, the surface is domi-nated with adsorbed N atoms and K r is small (! 1) and increases with increasing temperature.…”

Section: Catalysis Onlymentioning

confidence: 99%

Leveraging Expertise in Thermal Catalysis to Understand Plasma Catalysis

Lefferts

2024

Angew Chem Int Ed

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Best practices in testing heterogeneous catalysts are translated to plasma‐catalytic experiments. Independent determination of plasma‐catalytic and plasma‐chemical contributions is essential. Non‐porous catalyst particles are preferred because active sites inside sub‐micron pores cannot contribute. Temperature variation is needed to determine kinetics, despite the complexity of thermal effects in plasma. Rigorous checks on catalyst deactivation and mass balance are needed. Plasma enhanced reversed reactions should be minimized by keeping conversion low and far from thermodynamic equilibrium, preventing underestimation of the rate of forward reaction. In contrast, plasma‐catalytic studies often aim at conversions surpassing thermodynamic equilibrium, not obtaining any information on kinetics. Calculation of catalyst activity per active sites (turn‐over‐frequency) requires also appropriate characterization to determine the number of active sites.The relationship between kinetics and thermodynamics for plasma‐catalysis is discussed using endothermic decomposition of CO2 and exothermic synthesis of ammonia from N2 and H2 as examples. Assuming Langmuir–Hinshelwood and Eley‐Rideal mechanisms, the effect of excitation of reactant molecules on activation barriers and surface coverages are discussed, influencing reaction rates. The consequences of reversed reactions are considered. Plasma‐catalysis with catalysts applied for thermal catalysis at much higher temperature should be avoided, as adsorbed species are bonded too strongly resulting in low rates.

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Section: Catalysis Onlymentioning

confidence: 99%

Leveraging Expertise in Thermal Catalysis to Understand Plasma Catalysis

Lefferts

2024

Angew Chem Int Ed

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Studies of Phase Transformation Kinetics in the System of Nanocrystalline Iron/Ammonia/Hydrogen at the Temperature of 350 °C by Means of Magnetic Permeability In Situ Measurement

Arabczyk,

Pelka,

Brzoza-Kos

et al. 2024

Applied Sciences

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The kinetics of phase transformations in the nitriding process α-Fe → γ’-Fe4N → ε-Fe3-2N of the pre-reduced iron ammonia synthesis catalyst was investigated under in situ conditions (atmospheric pressure, 350 °C) by measuring changes of mass, gas phase composition, and magnetic permeability in a differential tubular reactor. The iron nanocrystallite size distribution according to their specific active surface areas was measured, and it was found that the catalyst is bimodal as the sum of two Gaussian distributions, also differing in the value of the relative magnetic permeability. Relative magnetic permeability of small α-Fe crystals in relation to large crystals is higher by 0.02. In the area of α → γ’ transformation, the magnetic permeability dependencies change, proving the existence of two mechanisms of the α-Fe structure change in the α-Fe → γ’-Fe4N transformation. In the first area, a solution of α-Fe (N) is formed with a continuous and insignificant change of the crystal lattice parameters of the iron lattice. In the second area, there is a step, oscillatory change in the parameters of the iron crystal lattice in FexN (x = 0.15, 0.20, 0.25 mol/mol). In the range of γ’-Fe4N → ε-Fe3-2N transformation, a solution is formed, with nitrogen concentration varying from 0.25–0.45 mol/mol. During the final stage of the nitriding process, at a constant value of the relative magnetic permeability, only the concentration of nitrogen in the solution εr increases. The rate of the phenomenon studied is limited by a diffusion rate through the top layer of atoms on the surface of iron nanocrystallite. The estimated value of the nitrogen diffusion coefficient varied exponentially with the degree of nitriding. In the area of the solution, the diffusion coefficient is approximately constant and amounts to 5 nm2/s. In the area of oscillatory changes, the average diffusion coefficient changes in the range of 3–11 nm2/s, and is inversely proportional to the nitrogen content degree. The advantage of the research method proposed in this paper is the possibility of simultaneously recording, under reaction conditions, changes in the values of several process parameters necessary to describe the process. The research results obtained in this way can be used to develop such fields of knowledge as heterogeneous catalysis, materials engineering, sensorics, etc.

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Fused Catalysts

Abstract: The sections in this article are Introduction The Concept of Fused Catalysts Thermodynamic and Kinetic Considerations Sulfuric Acid Catalyst Metallic Glasses Tribochemistry Mesostructure of Fused Catalyst Materials

Cited by 2 publications

References 61 publications

Leveraging Expertise in Thermal Catalysis to Understand Plasma Catalysis

Leveraging Expertise in Thermal Catalysis to Understand Plasma Catalysis

Studies of Phase Transformation Kinetics in the System of Nanocrystalline Iron/Ammonia/Hydrogen at the Temperature of 350 °C by Means of Magnetic Permeability In Situ Measurement

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