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The tightening standards of nitrogen oxides emission from industrial plants encourage nitric acid producers to search for new efficient solutions to meet the stringent emission limits. Industrial practice and the patent literature show that the effectiveness of deNOx (SCR) and deN2O technology is affected not only by the type and shape of the catalyst, but also by the method of its installation in a heterogenous catalytic reactor. The article presents the background of the problem, related to the emission of nitrogen oxides from nitric acid plants, and describes the technology of the tail gases purified from NOx and N2O. It shows various aspects that should be considered in designing reactors for deNOx and deN2O processes in nitric acid plants. The advantages and disadvantages of different catalytic basket designs, their industrial application and the direction of their design development were also indicated. [ABSTRACT FROM AUTHOR]

Thecatalytic activity of a doubly promoted K/Zn–Co3O4spinel catalyst in the deN2O reactionwas tested for 10 weeks in a nitric acid pilot plant. A charge of15 kg of the catalyst was synthesized via precipitation method, dried,calcined, and formed into 5 × 5 mm tablets. The catalytic testswere carried out in the wide range of process parameters: 320 < T< 425 °C; 80 < VRG< 180 N m3·h–1, 3 < p< 9.5 bar(a). During the operation the chemical compositionof tail gases from ammonia oxidation reactor outlet varied withinthe following range: 300 < CN2O<1500 ppm(v); 30 < CNOx< 3000 ppm(v);10000 < CO2< 50000 ppm(v); 1000< CH2O< 18000 ppm(v); N2– rest. In these conditions, the N2O conversionwas above 70% at 400 °C and was stable in time. Fresh and usedcatalysts were compared through detailed structural and morphologicalcharacterization (XRD, Raman, BET, SEM, XPS, H2-TPR), andtheir deN2O performance was verified in laboratory conditions.Long-term catalytic tests proved persistent stability of the catalystwith respect to its high activity, composition, structure, and morphology. [ABSTRACT FROM AUTHOR]

Natural zeolite of the heulandite-type framework was modified with iron and tested as a catalyst for the selective catalytic reduction of nitrogen oxides with ammonia (NH3-SCR) in the temperature range of 150–450 °C. The catalyst was prepared at a laboratory scale in a powder form and then the series of experiments of its shaping into tablets was conducted. Physicochemical studies of the catalyst (N2 sorption at −196 °C, FT-IR, XRD, UV-vis) were performed to determine the textural and structural properties and identify the surface functional groups, the crystalline structure of the catalysts and the form and aggregation of the active phase. The activity tests over the shaped catalyst were performed industry-reflecting conditions, using tail gases from the pilot nitric acid plant. The influence of a temperature, catalyst load, and the amount of reducing agent (ammonia) on the NOx reduction process were investigated. The results of catalytic tests that were performed on model gas mixture showed that non-modified clinoptilolite exhibited around 58% conversion of NO at 450 °C. The temperature window of the shaped catalyst shifted to a higher temperature range in comparison to the powder sample. The catalytic performance of the shaped Fe-clinoptilolite in the industry-reflecting conditions was satisfactory, especially at 450 °C. Additionally, it was observed that the ratio of N2O concentration downstream and upstream of the catalytic bed was below 1, which indicated that the catalyst exhibited activity in both DeNOx and DeN2O process. [ABSTRACT FROM AUTHOR]