Catalysis ammonia oxidation

The most popular SCR catalyst formulations are those that were developed in Japan in the late 1970s comprised of base metal oxides such as vanadium pentoxide [1314-62-1J, V20, supported on titanium dioxide [13463-67-7] Ti02 (1). As for low temperature catalysts, NO conversion rises with increasing temperatures to a plateau and then falls as ammonia oxidation begins to dominate the SCR reaction. However, peak conversion occurs in the temperature range between 300 and 450°C, and the fah-off in NO conversion is more gradual than for low temperature catalysis (44). 

By far the most important use of the platinum metals is for catalysis. The largest single use is in automobile catalytic converters. Platinum is the principal catalyst, but catalytic converters also contain rhodium and palladium. These elements also catalyze a wide variety of reactions in the chemical and petroleum industry. For example, platinum metal is the catalyst for ammonia oxidation in the production of nitric acid, as described in Pt gauze, 1200 K... 

In view of the spectroscopic evidence available, particularly from coadsorption studies (see Chapter 2), ammonia oxidation at Cu(110) became the most thoroughly studied catalytic oxidation reaction by STM. However, a feature of the early STM studies was the absence of in situ chemical information. This was a serious limitation in the development of STM for the study of the chemistry of surface reactions. What, then, have we learnt regarding oxygen transient states providing low-energy pathways in oxidation catalysis ... 

Bagnasco, G., Peluso, G., and Russo, G., Ammonia oxidation over CuO/Ti02 selectivity and mechanistic study, paper presented at the 3rd World Congress on Oxidation Catalysis, 1997, pp. 643-652. 

Sadykov VA, Isupova LA, Zolotarskii IA, Bobrova LN, Noskov AS, Parmon VN, Brushtein EA, Telyatnikova TV, Chernyshev VI, Lunin W. Oxide catalysts for ammonia oxidation in nitric acid production properties and perspectives. Applied Catalysis A General. 2000 204(l) 59-87. 

The ammonia-oxidizing bacteria oxidize ammonia to nitrous acid via hydroxyl-amine (NH2OH) (Lees, 1952 Hofman and Lees, 1953) ammonia is first oxidized to hydroxylamine by the catalysis of ammonia monooxygenase (AMO) (Dua et al., 1979 Hollocher et al., 1981). In this reaction, molecular oxygen is utilized. Then, hydroxylamine formed is oxidized to nitrous acid by the catalysis of hydroxylamine oxidoreductase (HAO). 

Ammonia monooxygenase catalyzes also the oxidation of methane (Hyman and Wood, 1983) and carbon monoxide (Tsang and Suzuki, 1982) to methanol and carbon dioxide, respectively, in addition to the catalysis of the oxidation of ammonia. The oxidation of methane by the enzyme will be described again below in relation to the regulation of the methane formation by the ammonia-oxidizing bacteria. 

Not all catalysts need the extended surface provided by a porous structure, however. Some are sufficiently active so that the effort required to create a porous catalyst would be wasted. For such situations one type of catalyst is the monolithic catalyst. Monolithic catalysis are normally encountered in processes where pressure drop and heat removal are major considerations. Typical examples include the platinum gauze reactor used in the ammonia oxidation ponion of nitric acid manufacture and catalytic converters used to oxidize pollutants in automobile exhaust. They can be porous (honeycomb) or nonporous (wire gauze). A photograph of an automotive catalytic converter i,s. shown in PRS Figure RU.1-2. Platinum is a primary catalytic material in the monolith. 

Aluminas are commonly used as acid catalysts and as support material for catalysts. Here, we will investigate the influence of the alumina support on ammonia adsorption in the ammonia oxidation reaction over Pt/7-alumina. Ammonia appears to be involved in a phenomenon called adsorption assisted desorption (AAD). Adsorption assisted desorption (AAD) has become well-known in catalysis. We foimd that the rate of desorption of ammonia is increased by the partial ammonia pressure in the gas phase. 

Ammonia Oxidation with Pt + Ion-Exchanged Zeolite Catalysts Catalysis Through Coordination Chemistry... 

Perez-Ramirez, J. and Vigeland, B. (2005). Lanthanum ferrite membranes in ammonia oxidation. Opportunities for pocket-sized nitric acid plants. Catalysis Today, Vol. 105, pp. 436-442. 

In 1920s, the studies on the catalysts for ammonia sjmthesis were performed sporadically in BASF, instead, the company mainly focused on the organic synthesis under high pressm-es and the new fields in heterogeneous catalysis. Dm-ing the development of ammonia synthesis catalysts, researchers provided valuable information about the dm-ability, thermal stability, sensitivity to poisons, and in particular to the concept of promoter. Mittasch smnmarized the roles of various additives as shown in Fig. 1.9. The hypothesis of successful catalyst is multi-component system proposed by Mittasch was confirmed to be very successful. Iron-chromium catalysts for water gas shift reaction, zinc hromium catalystfor methanol synthesis, bismuth iron catalysts for ammonia oxidation and iron/zinc/alkali catalysts for coal hydrogenation were successively developed in BASF laboratories. 

Metals and alloys, the principal industrial metalhc catalysts, are found in periodic group TII, which are transition elements with almost-completed 3d, 4d, and 5d electronic orbits. According to theory, electrons from adsorbed molecules can fill the vacancies in the incomplete shells and thus make a chemical bond. What happens subsequently depends on the operating conditions. Platinum, palladium, and nickel form both hydrides and oxides they are effective in hydrogenation (vegetable oils) and oxidation (ammonia or sulfur dioxide). Alloys do not always have catalytic properties intermediate between those of the component metals, since the surface condition may be different from the bulk and catalysis is a function of the surface condition. Addition of some rhenium to Pt/AlgO permits the use of lower temperatures and slows the deactivation rate. The mechanism of catalysis by alloys is still controversial in many instances. 

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