Selective catalytic reduction chemical

Emission control from heavy duty diesel engines in vehicles and stationary sources involves the use of ammonium to selectively reduce N O, from the exhaust gas. This NO removal system is called selective catalytic reduction by ammonium (NH3-SGR) and it is additionally used for the catalytic oxidation of GO and HGs.The ammonia primarily reacts in the SGR catalytic converter with NO2 to form nitrogen and water. Excess ammonia is converted to nitrogen and water on reaction with residual oxygen. As ammonia is a toxic substance, the actual reducing agent used in motor vehicle applications is urea. Urea is manufactured commercially and is both ground water compatible and chemically stable under ambient conditions [46]. 

Busca, G., Lietti, L., Ramis, G. et al. (1998) Chemical and mechanistic aspects of the selective catalytic reduction of NOx by ammonia over oxide catalysts A review, Appl. Catal. B Environ., 18, 1. 

V-Mo-Zeolite catalysts prepared by solid-state ion exchange were studied in the selective catalytic reduction of NOx by ammonia. The catalysts were characterized by chemical analysis, X-ray powder diffraction, N2 adsorption (BET), DRIFT, UV-Vis and Raman, spectroscopy and H2 TPR. Catalytic results show that upon addition of Mo to V-ZSM-5, catalytic performance was enhanced compared to V-ZSM-5. 

Selected ion monitoring mode, mass spectrometer, 6 431 Selection, in chemical product design, 5 759, 772-776 Selective carburizing, 76 205 Selective catalytic reduction (SCR), 77 719-720, 79 626 See also Nonselective catalytic reduction SCR entries... 

The present chapter will primarily focus on oxidation reactions over supported vanadia catalysts because of the widespread applications of these interesting catalytic materials.5 6,22 24 Although this article is limited to well-defined supported vanadia catalysts, the supported vanadia catalysts are model catalyst systems that are also representative of other supported metal oxide catalysts employed in oxidation reactions (e.g., Mo, Cr, Re, etc.).25 26 The key chemical probe reaction to be employed in this chapter will be methanol oxidation to formaldehyde, but other oxidation reactions will also be discussed (methane oxidation to formaldehyde, propane oxidation to propylene, butane oxidation to maleic anhydride, CO oxidation to C02, S02 oxidation to S03 and the selective catalytic reduction of NOx with NH3 to N2 and H20). This chapter will combine the molecular structural and reactivity information of well-defined supported vanadia catalysts in order to develop the molecular structure-reactivity relationships for these oxidation catalysts. The molecular structure-reactivity relationships represent the molecular ingredients required for the molecular engineering of supported metal oxide catalysts. 

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, . 

Selective catalytic reduction (SCR) has been used to control NO emissions from utility boilers in Europe and Japan for over a decade. Applications of SCR to control process NO emissions in the chemical industry are becoming increasingly common. A typical SCR system is shown in Fig. 22-24. 

It appears interesting to investigate vanadia doped sulfated Ti-pillared clay for the selective catalytic reduction of NO by anmionia and to compare their performance with sulfated Ti-pillared clay and vanadia doped Ti-pillared clay. In this work, all the catalysts were synthesized under identical conditions and were characterized by different techniques. These techniques included surface area measurement, pore size distribution, X-ray diffraction. X-ray photoelectron spectroscopy, TPD-NH3 and chemical analysis of Ti retained by the clay. The catalysts were then tested in the selective catalytic reduction of NO by ammonia in the presence of oxygen at different temperatures. 

Preparation of vanadium-based catalysts for selective catalytic reduction of nitrogen oxides using titania supports chemically modified with organosilanes... 

Preparation of vanadium-based catalysts for selective catalytic reduction of nitrogen oxides using titania supports chemically modified with organosilanes H. Kominami, M. Itonaga, A. Shinonaga, K. Kagawa, S. Konishi and Y. Kera 1089... 

Further reductions in NO levels can be achieved by removing NO from the turbine exhaust using selective catalytic reduction (SCR) with ammonia. SCR is an effective method for NO control that can reduce NO levels to about 10 ppm, usually in combination with water or steam injection or lean premix combustors. However, SCR is an expensive technology and the storage and handling of ammonia, a toxic chemical, also pose problems. Possible future restrictions on ammonia emissions may also limit the applieation of this technology. 

The most widely used post combustion technology for air emissions control of NOx (NO and NO2) where stringent regulations prevail is the selective catalytic reduction (SCR) of NOx with ammonia. The desired (selective) chemical reactions involved may be written as ... 

Metal oxide catalysts are extensively employed in the chemical, petroleum and pollution control industries as oxidation catalysts (e.g., oxidation of methanol to formaldehyde, oxidation of o-xylene to phthalic anhydride, ammoxidation of propylene/propane to acrylonitrile, selective oxidation of HjS to elemental sulfur (SuperClaus) or SO2/SO3, selective catalytic reduction (SCR) of NO, with NHj, catalytic combustion of VOCs, etc.)- A special class of metal oxide catalysts consists of supported metal oxide catalysts, where an active phase (e.g., vanadium oxide) is deposited on a high surface area oxide support (e.g., alumina, titania, ziiconia, niobia, ceria, etc.). Supported metal oxide catalysts provide several advantages over bulk mixed metal oxide catalysts for fundamental studies since (1) the number of surface active sites can be controlled because the active metal oxide is 100% dispersed on the oxide support below monolayer coverage,... 

Many of recent works on the plasma-catalyst process for NQr removal arc based on PCC system. Because of the similarity in the catalytic reactions between the PEC process and the conventional SCR process, NO.r removal method using PEC system is also referred to as plasma-enhanced selective catalytic reduction (PE-SCR) process [109], Table 4 summarizes the current status of NO r removal using the PE-SCR process. It should be noticed that the use of proper chemical reducing agent is necessary to achieve reductive decomposition of NO.r even with the plasma-catalyst system. To optimize the reductive decomposition of NO.r, therefore, it is necessary to find proper reducing agent together with a catalyst. The main role of NTP in the PEC system is the partial conversion of NO to NO . This partial oxidation of... 

Catalyst monoliths are also effective in the control of air pollution from stationary sources. They have been used for many years to oxidize hydrocarbon vapors in the vent streams from chemical plants and to reduce solvent emissions from printing and cleaning processes. More recent applications include CO removal from gas turbine exhaust and the selective catalytic reduction of NO in flue gas. Performance curves for the oxidation of various compounds over a Pt/Al203 catalyst are shown in Figure 10.5, where the conversion is plotted against the feed temperature. The reactors operate adiabatically, and the exit temperature may be 10-100°F above the feed temperature. At first, the conversion increases exponentially with temperature, as expected from the Arrhenius relationship. The decrease in slope... 

Figure 9.3 The efficiency of cobalt-exchanged high silica stilbite (Co-TNU-10) for the selective catalytic reduction of NO to N2 with methane as a function of temperature at different inlet CH4 levels of 2400 ( ), 8000 (A) and 16000 ( ) ppm. The reactions were run with a feed containing 1200ppm NO, 2.6% O2 and 10% H2O at a GHSV of 14000h 1. [Reproduced from reference 36 with permission. Copyright 2004 American Chemical Society.]...

Although the main applications of zeohtic sohds in catalysis will continue to be as solid acids in the synthesis and transformations of petrochemicals and commodity chemicals they continue to be considered as catalysts and catalyst supports for a range of reactions of synthetic and industrial relevance. The most important of these are of titanium- and tin-containing solids in selective oxidations. Other well-studied reactions over zeohtes include light hydrocar-bons-to-aromatics (Ga-zeolites) selective catalytic reduction of NO (transition metal exchanged zeolites) C C bond formation (Pd zeohtes) selective alkane oxyfunctionalisation with air (MAPOs, M Mn, Fe, Co) and chiral catalysis over encapsulated chiral complexes. 

Furthermore, a very active research field in zeolites with great potential is the reduction of nitrogen oxides by selective catalytic reduction, especially when focused on small-pore, hydrothermaUy stable zeohtes. Table 8.1 illustrates some interesting applications of zeohtes in the production of chemicals and fine chemicals and in emerging energy and environmental sustainable applications. 

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