Rafał Pelka

The effect of iron nanocrystallites' size in catalysts for ammonia synthesis on nitriding reaction and catalytic ammonia decomposition

Iron catalyst for ammonia synthesis of various mean sizes of iron nanocrystallites were nitrided with ammonia in a differential reactor equipped with systems that made it possible to conduct both thermogravimetric measurements and hydrogen concentration analyses in the reacting gas mixture. The nitriding process was investigated under atmospheric pressure at the temperature of 475°C. It was found that along with an increase of mean size of iron nanocrystallites, with a decrease of specific surface area of the samples, nitriding degree of solid samples increased. At the same time the rate of surface reaction of catalytic ammonia decomposition decreased. Along with an increase of the samples’ specific surface area an increase of the catalyst’s activity was observed. However, it was also observed that the concentration of active sites on the catalysts’ surface decreased along with an increase of specific surface area.

Adsorption of Ni2+ from aqueous solution by magnetic Fe@graphite nano-composite

Abstract The removal of Ni2+ from aqueous solution by iron nanoparticles encapsulated by graphitic layers (Fe@G) was investigated. Nanoparticles Fe@G were prepared by chemical vapor deposition CVD process using methane as a carbon source and nanocrystalline iron. The properties of Fe@G were characterized by X-ray Diffraction method (XRD), High-Resolution Transmission Electron Microscopy (HRTEM), Fourier Transform-Infrared Spectroscopy (FTIR), BET surface area and zeta potential measurements. The effects of initial Ni2+ concentration (1–20 mg L−1), pH (4–11) and temperature (20–60°C) on adsorption capacity were studied. The adsorption capacity at equilibrium increased from 2.96 to 8.78 mg g−1, with the increase in the initial concentration of Ni2+ from 1 to 20 mg L−1 at pH 7.0 and 20oC. The experimental results indicated that the maximum Ni2+ removal could be attained at a solution pH of 8.2 and the adsorption capacity obtained was 9.33 mg g−1. The experimental data fitted well with the Langmuir model with a monolayer adsorption capacity of 9.20 mg g−1. The adsorption kinetics was found to follow pseudo-second-order kinetic model. Thermodynamics parameters, ΔHO, ΔGO and ΔSO, were calculated, indicating that the adsorption of Ni2+ onto Fe@G was spontaneous and endothermic in nature.

Utilization of spent iron catalyst for ammonia synthesis

Utilization of spent iron catalyst for ammonia synthesis Several methods of the utilization of spent iron catalyst for ammonia synthesis have been presented. The formation of iron nitrides of different stoichiometry by direct nitriding in ammonia in the range of temperatures between 350°C and 450°C has been shown. The preparation methods of carbon nanotubes and nanofibers where iron catalyst catalyse the decomposition of hydrocarbons have been described. The formation of magnetite embedded in a carbon material by direct oxidation of carburized iron catalyst has been also presented.

Study of the kinetics of carburisation and nitriding of nanocrystalline iron

In the course of nitriding process of nanocrystalline iron that was promoted with aluminium and calcium oxides, nitrides such as Fe4N and Fe3–2N were created. In the process of carburisation, carbide Fe3C was created. The nanocrystalline iron nitriding and carburisation process rate was studied making use of the flow differential tubular reactor with thermogravimetric measurement of mass changes. Nitriding and carburisation process rates were limited by dissociative adsorption rate on the surface of iron and were dependent on the crystallite surface to crystallite volume ratio. Assuming the adsorption is the rate limiting step, the numerical simulations were performed. Theoretical considerations were compared with the experimental results of the iron nitriding or carburisation reaction. Kinetics and thermodynamic parameters of nitriding and carburisation were determined.