Nitrogen catalytic removal

Peng, X., Lin, H., Huang, Z. et al. (2006) Effect of catalysis on plasma assisted catalytic removal of nitrogen oxides and soot, Chem. Eng. Technol. 29, 1262-6. 

The potential for catalytic removal of nitrate was introduced in the late eighties and bears some similarity to the electrochemical process in as much as both involve stepwise reduction of the nitrogen oxidation state via formation of nitrites, ammonia and N2. As with the electrochemical process, the major drawback is the potential for formation of undesired products such nitrite and ammonium which must be depleted at more stringent levels than the nitrate itself... 

Most of the existing processes for nitrogen oxide removal are chemically based requiring high temperature or expensive catalysts. The main techniques involve either selective noncatalytic reduction (SNCR) or selective catalytic reduction (SCR). SNCR uses ammonia for conversion of NO to N2 and H20 at elevated temperatures (550-850 K). SCR can use catalysts such as Ti02 with active coatings of V2Os and WO, . 

In hydrotreating processes heteroatoms, such as sulphur, nitrogen, oxygen and metals, are catalytically removed from heavy oil residua. These metals, mainly vanadium and nickel, remain in the reactor as solid deposits accumulating on the catalyst surface after decomposition of the organo-metallic compounds. 

Postformation nitrogen oxide emission control measures include selective catalytic and noncatalytic reduction with ammonia, which between them are used by some 900 power station installations worldwide [51]. The catalytic removal methods are 70-90% efficient at NOx removal, but are more expensive to operate than the noncatalytic methods which are 30-80% efficient. Ammonia or methane noncatalytic reduction of NOx to elemental nitrogen is also an effective method which is cost-effective for high concentration sources such as nitric acid plants (Chap. 11). NOx capture in packed beds is less expensive, but this method is not particularly effective [23]. It is also not a very practical method either for utilities or for transportation sources. Two-stage scrubbing has also been proposed as an effective end-of-pipe NOx control measure. The first stage uses water alone and the second uses aqueous urea. 

Basic nitrogen species present on the surface of activated carbons or carbon fibers, like in the case of H2S, were found to enhance the sulfur dioxide uptake. Polyacrylonitrile (PAN)-based activated carbon fibers are examples of good adsorbents for SO2 removal [82, 92]. Although role of nitrogen present in the carbon matrix was not emphasized by Lee and coworkers [93] in their studies of SO2 adsorption on PAN-based activated carbon fibers, [93] Kawabuchi and coworkers noticed a significant increase in the sorption capacity when activated carbon fibers were modified with pyridine and basic nitrogen functionalities were introduced to the surface [93]. Pyridine provided basic functionality, which increased catalytic removal of SO,. . 

Supported ruthenium carbido-cluster catalysts for the catalytic removal of nitrogen monoxide and sulfur dioxide the preparation process monitored by sulfur K-edge X-ray absorption near-edge structure... 

Catalytic removal of nitrogen oxides [1] and sulfur oxides [2] is one of the most important issues in environmental problems. We have investigated supported ruthenium carbido-cluster catalysts derived from [RUjC(CO),J crystal. The supported cluster was... 

Tlhe catalytic removal of nitrogen oxides from automotive exhaust gases has been the subject of many studies. Catalysts containing at least 20 different metals, alone and in combination, have been tested. We found that the support used in catalyst preparation is as important as the metal, particularly in catalyst selectivity toward nitrogen rather than ammonia in strongly reducing streams. This paper is a report on some of the effects of support chemistry in a fairly well known system, platinum-promoted nickel (I). We also elucidate the pathways of ammonia removal in this system. 

Recent studies on the use of ammonia-treated activated carbon fibers or cloth for the catalytic removal of SO2 have shown that the activity increases with the amount of basic nitrogen groups present [104-106]. In particnlar, it was fonnd that the more basic pyridinic groups are the most active for the catalytic oxidation of SO2 both into SO3 and H2SO4 [107], and a linear correlation between the activity (normalized by the BET surface area) and the concentration of pyridinic groups was obtained, as shown in Fignre 6.7. 

The results in Table 7.6 confirm that the catalytic activity of carbon blacks in the oxidation of sulfurous acid is inferior to that of activated carbons. Carbon blacks that had been extracted with hot xylene to remove adsorbed organic molecules and subsequently heat-treated under Ar at 873 K were catalytically inactive. However, weak catalytic activity was observed after heat treatment of these carbon blacks at 1473 K, with the notable exception of an acetylene black that is free of nitrogen. Catalytic activity was also observed with the as-delivered carbon blacks after heat treatment at 973 to 1073 K. 

The catalytic removal of nitrogen oxides (NOx) is a technology urgently required for the protection of our atmospheric environment. The catalytic reduction of nitrogen... 

Heidenreich S, Nacke M, Hackel M, and Schaub G. Catalytic filter elements for combined particle separation and nitrogen oxides removal from gas streams. Powder Technol. 2008 180 86-90. 

Teraoka, Y., Nakano, K., Shangguan, W.F., and Kagawa, S. (1996) Simultaneous catalytic removal of nitrogen oxides and diesel soot particulate over perovskite-related oxides. Catal Today, 27, 107-113. 

Jones J, Ross J. The Development of Supported Vanadia Catalysts for the Combined Catalytic Removal of the Oxides of Nitrogen and of Chlorinated Hydrocarbons from Flue Gases. Catal Today 1997 35 97-105. 

Naphtha Hydrotreating. Heavy naphthas generally have low octane munbers, often less than 60 RON. To raise the octane, refiners use catalytic reforming units. Alternatively, heavy naphtha can go to an isomerization unit, which also makes high-octane products. In both reforming and isomerization, the catalysts are sulfur-sensitive, so a naphtha hydrotreater is used to lower the feed sulfur content, usually to <1 wppm. Some nitrogen is removed, too, which also is beneficial. 

Tronconi, E., Forzatti, R, Gomez Martin, J.R, and MaUoggi, S. Selective catalytic removal of nitrogen oxide (NO ) A mathematical model for design of catalyst and reactor. Chem. Eng. Sci. 1992, 47, 2401-2406. 

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