Adsorption of reaction species for hydrogenation of o-nitrotoluene on copper chromite under catalytic conditions

Abstract

Adsorption of reaction species involved in vapour phase hydrogenation of o-nitrotoluene (viz. o-nitrotoluene, o-toluidine and water) on copper chromite in presence of an inert gas (He) or hydrogen (which is one of the reactants) at temperature (473-560 K) and partial pressures at which the catalytic reaction is carried out has been investigated using the gas chromatographic pulse technique. The presence of hydrogen was found to cause a very significant decrease in the adsorption of toluidine but a little effect on the adsorption of water. The adsorption data for all the reaction species could be fitted to the Freundlich adsorption equation. The isoteric heats of adsorption obtained from the adsorption isotherm indicated that o-toluidine and water are physically absorbed, whereas o-nitrotoluene is chemisorbed on the catalyst. The heat of adsorption of water and o-nitrotoluene was found to decrease with the increase in the surface coverage, indicating repulsive interactions between the adsorbed species. On the other hand the heat of adsorption of o-toluidine (in presence or absence of H₂) was found to increase with the increase in the surface coverage, suggesting attractive interactions between the absorbed species.