Emission-control catalyzer

I.V. Yentekakis, R.M. Lambert, M.S. Tikhov, M. Konsolakis, and V. Kiousis, Promotion by sodium in emission control catalysis A kinetic and spectroscopic study of the Pd-catalyzed reduction on NO by propene, J. Catal. 176, 82-92 (1998). 

In industry many selective oxidations are carried out in a homogeneously catalyzed process. Heterogeneous catalysts are also applied in a number of processes, e.g. total combustion for emission control, oxidative coupling of methane, the synthesis of maleic acid from butanes, the epoxidation of ethylene. Here we focus upon heterogeneous catalysis and of the many examples we have selected one. We will illustrate the characteristics of catalytic oxidation on the basis of the epoxidation of ethylene. It has been chosen because it illustrates well the underlying chemistry in many selective oxidation processes. 

Another emission control aspect of diaphragm cell operation concerns the use of the crude cell product, still containing sodium chloride, to carry out base-catalyzed reactions such as ring closure of propylene chlorohydrin (Eq. 8.27) or hydrolysis of chlorobenzene (Eq. 8.45). 

Alumina, alkaline-earth oxides, mixed oxides (spinels), rare-earth oxides, and lanthanide ores are known additives capable of sorbing S-impurities. The properties of these materials can be manipulated to produce catalysts capable of reducing up to -80% S-emissions and meet the refiner needs. It is, however, unlikely that these systems will be capable of satisfying the more stringent environmental S-emission standards expected in the future. Details of the reaction mechanism by which additives and promoters catalyze the oxidative sorption of S-impurities and details of catalyst deactivation have not yet been proposed. This work could provide useful information to help design more efficient S-transfer catalysts. The catalytic control of S-emissions from FCC units has been described in detail in two papers appearing in this volume (46,47) and in the references given (59). 

The CL emission of Scheme 3 catalyzed by HRP can be applied to the quantitative analysis of catecholamines, such as dopamine (68), epinephrine (132), L-DOPA (30), norepinephrine (133), deoxyepinephrine (134) isoproterenol (135) and dihydroxybenzy-lamine (136), in a FIA system, after undergoing the oxidation shown for dopamine (68) in equation 20. The mechanism of this process is not totally clear however, the CL yields of equation 20 depend upon the pH of the system (pH 9 is convenient and is achieved by adjusting the concentration of imidazole), the temperature (60 °C is adequate) and the structure of the analyte (a calibration curve is needed for each one). Taking 68 as reference (100%) the CL yields after 30 min incubation (achieved by controlling the flow through a long capillary mbe) are as shown in equation 42 A5i... 

The noncatalytic reduction of nitric oxide by insitu formed char is considered one of the significant reactions which control nitric oxide emission and a detailed kinetic study was carried out. (2, 3, 4) The present authors demonstrated that this reaction proceeded even under an excess air condition and that the rate is enhanced by the coexisting oxygen up to 750°C. (.5,6) Besides the noncatalytic reaction, carbon monoxide may have a significant effect on nitric oxide reduction by char. (2.) Roberts et al.(8) reported that the gas phase reactions in the nitric oxide reduction play a minor role and that the absence of a major gas phase reaction of NO and coal nitrogen into N2 requires the participation of a surface which catalyzes reactions. Char is considered to... 

In 1980 additional regulations imposed by the U.S. Environmental Protection Agency (EPA) required control of NOx (NO, N02, N20) emissions. Its removal coupled with the continuing need to remove CO and CyHn proved to be quite challenging because the latter had to be oxidized and the former reduced. Thus it appeared two separate environments were needed. This problem was solved by the development of the three-way catalyst or TWC capable of catalyzing the conversion of all three pollutants simultaneously provided the exhaust environment could be held within a narrow air-to-fuel range. This is shown in Fig. 7.10. 

The assay is performed in Mcllvaine buffer (0.2 M disodium hydrogen phos-phate/0.1 M citric acid pH 7.0) with 2mM GSH (stock solution 60.1 mg/ml), 0.5 mAf GSSG (stock solution 30.7 mg/ml), and 5 xAf Pf PDO (stock solution, 1.0 mg/ml in Tris-Cl pH 8.4). It is placed in a fluorescence cuvette with a final assay volume of 1 ml. After mixing, the cuvette is placed in a thermostatically controlled Perkin-Elmer LS50B spectrofluorimeter for 1 min to allow thermal equilibration of the solution to 50°C. Next, 5 p,M substrate peptide (1.05 mM, in 30% acetonitrile/0.1% TFA) is added, mixed, and the change in fluorescence intensity (excitation 280 nm, emission 350 nm, slits 5/5 nm) is monitored over an appropriate time (15 min) 900 data points are collected. As a control, the same experiment is carried out in the absence of Pf PDO and the decrease in fluorescence intensity is not observed (Fig. 2). At pH 8.0 the spontaneous oxidation of the peptide substrate is observed, presumably due to air oxidation, but at pH 7.0 only the catalyzed oxidation of the substrate is measured. 

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