Disclosed is an apparatus for conversion of ammonia into oxides of nitrogen which may comprise an adiabatic burner (108), a set of platinum/rhodium alloy catalytic gauzes (102A), (102B), and (102C), a waste heat recovery boiler (WHRB) (110), an absorption tower (302A), (302B), (302C), (302D) and (302E), a NaOH tank (306) and a surge tank (304). Further, the adiabatic burner may be configured to carry out catalytic oxidation of air and ammonia, using catalytic gauzes (102A), (102B), and (102C) of platinum/rhodium alloy. Further, the mixture of air and ammonia may be selectively oxidized to oxides of nitrogen, which may be absorbed in an alkali medium in the absorption tower (302A), (302B), (302C), (302D) and (302E), to yield sodium nitrites and nitrates.

Integrated process for the synthesis of ammonia and nitric acid including: a) production of an ammonia make-up synthesis gas, comprising steam reforming of a hydrocarbon feedstock under provision of steam reforming heat; catalytic conversion of said make-up synthesis gas into ammonia; catalytic oxidation of a stream of ammonia obtaining a process gas; absorption of said process gas with water obtaining nitric acid, wherein at least a portion of the steam reforming heat is recovered from said hot process gas.

A high energy recovery process in nitric acid production process recovers, utilizes and/or stores heat energy in at least four stages. In the first stage, a first heat energy is recovered at the catalytic oxidation of ammonia to nitric oxide to generate high-pressure steam used for a first electrical power generation. A second heat energy is recovered at the catalytic oxidation of nitric oxide to nitrogen dioxide to generate low-pressure steam used for a second electrical power generation in the second stage. The nitrogen dioxide is further cooled in a condenser and a third heat energy is recovered and stored in a thermal storage via a heat pump. The nitrogen gas is absorbed to produce nitric acid in an absorber resulting in a hot tail gas stream. The hot tail gas stream is expanded over a tail gas turbine for a third electrical power generation.

A process for preparing nitric acid may involve vaporizing ammonia in at least one first ammonia vaporizer to produce an ammonia gas, oxidizing this ammonia gas to nitrogen dioxide in a plant section of a nitric acid plant, and absorbing the nitrogen dioxide in water to produce nitric acid. A residual gas containing nitrous gases may be taken off from the plant section of the nitric acid plant and conveyed to a residual-gas cleaning apparatus. The residual gas containing nitrous gases may be reduced by means of ammonia in the residual-gas cleaning apparatus, wherein ammonia-containing wastewater obtained in the at least one first ammonia vaporizer may be conveyed to the residual-gas cleaning apparatus. Such a process may eliminate or at least substantially reduce ammonia-containing wastewater. Furthermore, a plant can be used in this process for preparing nitric acid.

An apparatus and a process for reducing the concentration of NOx nitrogen oxides in residual gas may be employed during shutdown and/or startup of apparatuses for preparing nitric acid. An example apparatus for reducing NOx nitrogen oxides may include a reactor that produces NOx nitrogen oxides, an absorption apparatus that absorbs at least part of the NOx nitrogen oxides produced in an aqueous composition, a residual gas purification plant that decomposes and/or reduces unabsorbed NOx nitrogen oxides, feed means for feeding the NOx nitrogen oxides to the absorption apparatus, discharge means for discharging the unabsorbed NOx nitrogen oxides from the absorption apparatus to the residual gas purification plant, and a bypass that transfers a gas mixture from the reactor to the residual gas purification plant while bypassing the absorption apparatus during startup and/or shutdown of the apparatus for preparing nitric acid.

A process for preparing nitric acid may involve vaporizing ammonia in at least one first ammonia vaporizer to produce an ammonia gas, oxidizing this ammonia gas to nitrogen dioxide in a plant section of a nitric acid plant, and absorbing the nitrogen dioxide in water to produce nitric acid. A residual gas containing nitrous gases may be taken off from the plant section of the nitric acid plant and conveyed to a residual-gas cleaning apparatus. The residual gas containing nitrous gases may be reduced by means of ammonia in the residual-gas cleaning apparatus, wherein ammonia-containing wastewater obtained in the at least one first ammonia vaporizer may be conveyed to the residual-gas cleaning apparatus. Such a process may eliminate or at least substantially reduce ammonia-containing wastewater. Furthermore, a plant can be used in this process for preparing nitric acid.

A catalytic structure has a substrate and a plurality of high-entropy alloy (HEA) nanoparticles. At least a surface layer of the substrate is formed of a metal oxide. The HEA nanoparticles can be formed on the surface layer. Each HEA nanoparticle can comprise a homogeneous mixture of at least four different elements forming a single-phase solid-solution alloy. The catalytic structures can be used to catalyze a chemical reaction, such as an ammonia oxidation reaction, an ammonia synthesis reaction, or an ammonia decomposition reaction.