EFFECT OF WATER ON THE KINETICS OF NITRIC-OXIDE REDUCTION OVER A HIGH-SURFACE-AREA V2O5/TIO2 CATALYST

The influence of water on the kinetics of nitric oxide reduction with ammonia over a V2O5/TiO2 catalyst has been investigated at different water partial pressures (0-300 Pa). An integral reactor operating at space velocity (sv) of 900 000 h-1 was employed. Nitric oxide and ammonia initial partial pressures were 10-200 Pa, oxygen 2700 Pa; the temperature ranged from 250 to 350-degrees-C. It has been found that the presence of water in the feed affects the reaction rate, inhibiting it. Two types of kinetic models based on a reaction mechanism involving the formation of a nitrosamidic intermediate compound were developed by assuming the adsorption of water as a reversible or irreversible step. Langmuir, Freundlich and Temkin equations for water adsorption were introduced in the kinetic models. It has been found that a kinetic model based on the irreversible adsorption of water following a Temkin isotherm allows the kinetics of nitric oxide reduction to be described for the whole range of water partial pressures. These results were interpreted according to a poisoning effect of the ammonia adsorbing sites by water.