Cobalt–zinc spinel dispersed over cordierite monoliths for catalytic N2O abatement from nitric acid plants

Abstract

A series of monolithic catalysts with the 0.3wt.% loading of the (Co,Zn)Co2O4 spinel active phase dispersed on bare and ceria and zincite washcoated cordierite substrates was prepared by impregnation method: (Co,Zn)Co2O4/cordierite, (Co,Zn)Co2O4/ZnO/cordierite and (Co,Zn)Co2O4/CeO2/cordierite. The catalysts were thoroughly characterized (XRD, RS, SEM/TEM/EDX, XRF), and their catalytic deN2O activity was investigated using model gas mixture (2000ppm N2O/N2), and tail gases (1400±50ppm N2O, 900±100ppm NOx, 0.8±0.2vol.% H2O, 2.0±0.2vol.% O2) of the nitric acid pilot plant. The reported data points correspond to the measurements performed at possibly the closest tail gas composition. Morphological SEM analysis of the monolith cross-sections indicated the segregation of both ZnO and CeO2 washcoats in the form of islands covered by the (Co,Zn)Co2O4 active phase. The catalytic tests revealed that the monolithic catalysts exhibit high catalytic deN2O activity, reaching X>96% at 400°C (model gas) and 450°C (tail gases) for the best (Co,Zn)Co2O4/CeO2/cordierite system. It was also found that the specific reaction rate per cobalt spinel weight loading for the monolithic catalysts is even two orders of magnitude higher than in the case of the optimized bulk spinel phase. Yet, the beneficial effect of ceria, dominant in the model gas mixture, is largely dumped in tail gases at low temperature. It is however restored above 400°C, when the poisoning H2O and NOx molecules are desorbed.