CATALYTIC DECOMPOSITION OF NITROUS OXIDE N?O ON ALUMINA-SUPPORTED RUTHENIUM CATALYST

Abstract

In this thesis, the alumina supported ruthenium catalysts (Ru/Al₂O3) have been prepared and the catalysts have been tested for high concentration N₂O decomposition. Along the catalytic evaluation, N₂O decomposition kinetics for this catalyst system has also been addressed. A rate expression for the N₂O decomposition developed on the basis of adsorption of N₂O on the catalyst surface is best correlated by the experimental data. The kinetic parameters determined from the experimental data obey the Arrhenius temperature dependency. The rate of N₂O decomposition is found to be first order with respect to the partial pressure of N₂O. The decomposition product O₂ exhibits no effect on the overall rate expression at high reaction temperature. As reaction temperature decreases, the effect of O₂ concentration on the rate of N₂O decomposition becomes noticeable. To test the Ru/Al₂O3 workability in real off-gas treatment from adipic acid production, a study of the decomposition of water-containing nitrous oxide gas has been carried out. Activation parameters of catalyst have been examined and two processes have been established using dry or wet N₂O (27 to 31 mol%) feed gases. After activation, N₂O can be decomposed in water vapour (up to 3 mol%) under optimal operational conditions. It is found that the effect of water is non-linear, and it can be significantly reduced at high operating temperature. The rate law of N₂O decomposition in wet environment can be expressed as first order in the partial pressure of nitrous oxide with an averaged apparent activation energy of 139 kJ/mol. Chemical composition, surface area and crystallographic structure of catalyst have been investigated with ICP/BET/ XRD/ FTIR. The studied catalysts are both chemically and hydrothermally stable. High conversion activity [1.2xl0² N₂º mmol (N₂O)·g⁻¹·h⁻¹ at 470.5°C (GHSV=14400 h⁻¹, N₂O 29.9 mol%, H₂O = 3.0 mol%, balanced with He)] has been found and an operational process of the catalyst has also been proposed.