Experimental investigation of mass transfer and pressure drop in NH3 SCR over self-supporting Cu-ZSM-5 foam

Abstract

Selective catalytic reduction of NO_x by NH₃ is an emerging technology for emission control applications worldwide. The development of structured catalysts for process intensification is of growing interest in catalytic processes due to heat and mass transfer limitations at an industrial scale. Self supported foam catalysts have increased active phase load in the structured reactor, without additional weight, reactor volume and pressure drop. The successful development of a self-supported catalyst could provide a ready-to-use material without the need of washcoating steps. A self supporting Cu-ZSM-5 foam catalyst is developed for NH₃ selective catalytic reduction (SCR) with high mechanical strength using an emulsion freeze casting method using hydrogenated vegetable oil as the oil phase and Cu-ZSM-5 slurry as the water phase. A comprehensive experimental study was conducted to understand the mass transfer and pressure drop characteristics of the foam catalysts. Correlations for the mass transfer coefficient and friction factor were derived for the foam catalyst and validated against the available data in the literature reviewed. A detailed investigation of key SCR reactions, NO_x storage and thermal stability and the inhibitory effects of feed gases, are carried out in this research. NO_x adsorption–desorption studies reveal that the presence of NO reduces the storage and thermal stability of stored nitrate in Cu-ZSM-5. Nitrate formation has an inhibition effect on NO oxidation and standard SCR due to the competitive adsorption.