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Abstract

The invention relates to a process and apparatus for preparing nitric acid by catalytic oxidation of NH₃ by means of oxygen and subsequent reaction of the NO_x formed with an absorption medium in an absorption tower, which comprises a catalyst bed for N₂O decomposition arranged in the process gas downstream of the catalytic NH₃ oxidation and upstream of the absorption tower in the flow direction and a catalyst bed for NO_x reduction and effecting a further decrease in the amount of N₂O arranged in the tailgas downstream of the absorption tower in the flow direction,

wherein the amount of N2O removed in the catalyst bed for N2O removal arranged in the process gas is not more than that which results in an N2O content of >100 ppmv and a molar N2O/NOx ratio of >0.25 before entry of the tailgas into the catalyst bed for NOx reduction andthe catalyst bed for NOx reduction and effecting a further decrease in the amount of N2O arranged in the tailgas contains at least one iron-loaded zeolite catalyst andNH3 is added to the tailgas before entry into the catalyst bed in such an amount that an NOx concentration of <40 ppmv results at the outlet from the catalyst bed andthe operating parameters are selected in such a way that an N2O concentration of <200 ppmv results.

First Claim