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

A series of monolithic catalysts with the 0.3 wt.% loading of the (Co,Zn)Co 2 O 4 spinel active phase dispersed on bare and ceria and zincite washcoated cordierite substrates was prepared by impregnation method: (Co,Zn)Co 2 O 4 /cordierite, (Co,Zn)Co 2 O 4 /ZnO/cordierite and (Co,Zn)Co 2 O 4 /CeO 2 /cordierite. The catalysts were thoroughly characterized (XRD, RS, SEM/TEM/EDX, XRF), and their catalytic deN 2 O activity was investigated using model gas mixture (2000 ppm N 2 O/N 2 ), and tail gases (1400 ± 50 ppm N 2 O, 900 ± 100 ppm NO x , 0.8 ± 0.2 vol.% H 2 O, 2.0 ± 0.2 vol.% O 2 ) 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 CeO 2 washcoats in the form of islands covered by the (Co,Zn)Co 2 O 4 active phase. The catalytic tests revealed that the monolithic catalysts exhibit high catalytic deN 2 O activity, reaching X > 96% at 400 °C (model gas) and 450 °C (tail gases) for the best (Co,Zn)Co 2 O 4 /CeO 2 /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 H 2 O and NO x molecules are desorbed. [ABSTRACT FROM AUTHOR]