Cobalt Spinel Catalyst for N 2 O Abatement in the Pilot Plant Operation-Long-Term Activity and Stability in Tail Gases Marek Inger, ‡ Marcin Wilk, ‡ Magdalena Saramok, ‡ Gabriela Grzybek,* ,† Anna Grodzka, † Pawel Stelmachowski, † Waclaw Makowski, † Andrzej Kotarba,* ,† and Zbigniew Sojka † † Faculty of Chemistry, Jagiellonian University in Krakow, Ingardena 3, 30-060 Krakow, Poland ‡ Fertilizers Research Institute, Al. Tysiąclecia Państwa Polskiego 13A, 24-110 Puławy, Poland ABSTRACT: 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. 1. INTRODUCTION Among many potential methods of the abatement of N 2 O emissions from nitric acid plants, the most effective from the economic point of view, are undoubtedly the catalytic approaches. In principle, two technical routes of N 2 O removal can be distinguished: a direct high-temperature decomposition of N 2 O from the process gases in an ammonia burner (HT- deN 2 O) and a low-temperature N 2 O removal from tail gases, either by using auxiliary reducing agents (NH 3 or hydro- carbons) or via direct decomposition (LT-deN 2 O). 1 Currently, most of the implemented projects relate to high-temperature pathway, encompassing more than 80% of all implementa- tions. 2 However, since in some installations this technology cannot be employed due to, e.g., space limitation in the ammonia burner, low-temperature approach becomes an attractive solution. In the case of LT-deN 2 O process the reactor is located after the absorption column, preferably after the tail gases heat exchangers and before the expander, not affecting the process of nitric acid production directly. As the temperature of the tail gases stream varies usually in the range of 200-500 °C, its additional heating would result in extra costs. 3 The temperature of the reaction can be decreased by the use of the reducing agents (hydrocarbons, ammonia, and even hydrogen). 1,5-8 Although the low-temperature solution is more expensive for investments, as it requires extra spending to build a reactor and sometimes also a heat exchanger, proper design of the reactor geometry may allow for obtaining high N 2 O conversions. Moreover, application of the low-temperature method is preferred in high pressure and dual pressure plants. The high pressure (above 10 bar in the absorption column) provides longer residence time in the reaction zone. In the case of the HT-deN 2 O method, especially in high pressure plants, the high load of catalyst gauzes by ammonia-air mixture and the lack of available volume in the ammonia burner lead to a poor reduction of the N 2 O emission. An average efficiency for the HT-deN 2 O method implemented in the high and the dual pressure plants is below 70%, but plants wherein the efficiency is below 50% also exist. At the same time, for the low pressure plants high-temperature reduction of N 2 O emission is usually greater than 85%. 2 The speci fic low-temperature N 2 O decomposition implementation depends on the features of individual installation, especially temperature and NO x concentration in the tail gas stream. Low-temperature catalytic decomposition of nitrous oxide was a subject of numerous extensive studies involving simple and mixed oxides, 9-11 perovskites, 12 spinels, 13-16 zeolites, 17 hydrotalcites, 18,19 mesoporous silica materials, 20 and various supported catalysts. 21-26 So far, one of the most promising systems for the low-temperature catalytic N 2 O removal is a modified cobalt spinel. 14,27-31 The optimization procedure of the multicomponent K/Zn-Co 3 O 4 spinel as deN 2 O catalyst is described in our previous works. 14,27,32 Industrial application requires shaping of this catalytic material, and long-term testing was carried out in the real conditions. The aim of this study was to investigate the deN 2 O performance of the developed doubly promoted spinel catalyst in a pilot scale as well as to evaluate possible structural, morphological, and surface changes of the catalyst during the long-term operation. The last point was achieved by thorough physicochemical characterization for the fresh and used catalysts (after pilot plant prolonged reactivity test). Received: April 8, 2014 Revised: May 30, 2014 Accepted: June 3, 2014 Published: June 3, 2014 Article pubs.acs.org/IECR © 2014 American Chemical Society 10335 dx.doi.org/10.1021/ie5014579 | Ind. Eng. Chem. Res. 2014, 53, 10335-10342