The catalytic activity of a doubly promoted K/Zn−Co 3 O 4 spinel catalyst in the deN 2 O reaction was tested for 10 weeks in a nitric acid pilot plant. A charge of 15 kg of the catalyst was synthesized via precipitation method, dried, calcined, and formed into 5 × 5 mm tablets. The catalytic tests were carried out in the wide range of process parameters: 320 < T < 425 °C; 80 < V RG < 180 N m 3 •h −1 , 3 < p < 9.5 bar(a). During the operation the chemical composition of tail gases from ammonia oxidation reactor outlet varied within the following range: 300 < C N2O < 1500 ppm(v); 30 < C NOx < 3000 ppm(v); 10000 < C O2 < 50000 ppm(v); 1000 < C H2O < 18000 ppm(v); N 2 − rest. In these conditions, the N 2 O conversion was above 70% at 400 °C and was stable in time. Fresh and used catalysts were compared through detailed structural and morphological characterization (XRD, Raman, BET, SEM, XPS, H 2 -TPR), and their deN 2 O performance was verified in laboratory conditions. Long-term catalytic tests proved persistent stability of the catalyst with respect to its high activity, composition, structure, and morphology.

The influence of Zn and K promoters on N 2 O decomposition over Co 3 O 4 was investigated by work function measurement and temperature-programmed surface reaction. The beneficial effect of the promoters resulting in spectacular decrease in the temperature of 50% conversion by 200°C was found to be essentially of electronic origin. The strong correlation between the catalyst work function and deN 2 O activity allowed for the optimization of the doping level of both additives. The pilot plant tests in real nitric acid tail gases revealed that the optimized double promoted (Zn, K) cobalt spinel catalyst maintained its remarkable activity in N 2 O decomposition (conversion [95% at the target temperature of 350°C) for more than 60 h.

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Catalytic high temperature decomposition (secondary abatement) of nitrous oxide over calcium aluminate 12CaO Á 7Al 2 O 3 (mayenite) was studied in the model laboratory tests (TPSR) and pilot units (steady-state) using the real feed. X-ray diffraction (XRD), scanning electron microscopy (SEM), N 2 -sorption (BET), electron paramagnetic resonance (EPR) and Raman spectroscopies were used to characterize the synthesized material. The catalyst exhibited high efficiency and selectivity in N 2 O removal, reaching practically 100% conversion at 1150 K without appreciable total losses of NO x . Owing to its high thermal stability and resistivity to sintering and low cost of production raw materials, mayenite was found to be a promising catalyst for economically appealing secondary abatement of nitrous oxide in nitric acid plants.

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