Catalytic control

J. K. Hochmuth and J. J. Mooney, Catalytic Control of Emissionsfrom M-8 5 Fueled Vehicles, SAE 930219, Society of Automotive Engineers,... 

G. Silver, J. E. Sawyer, and J. C. Summers, eds.. Catalytic Control of Air Pollution Mobile and Stationay Sources," ACS Symposium Series 495,1992. 

Catalytic Control of FOC Emissions, A Cost Effective Viable Technologyfor Industrial, Commercial and Waste ProcessingFacilities, Manufacturers of Emission... 

The relative FMO energies of the substrates of the 1,3-dipolar cycloaddition reaction of nitrones are important for catalytic control of the reaction. For the normal electron-demand 1,3-dipolar cycloaddition reactions the dominant FMO interac-... 

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). 

Catalytic Control of SO Emissions from Fluid Catalytic Cracking Units... 

The relative frontier molecular orbital (FMO) energies of the reagents are very important for the catalytic control of 1,3-dipolar cycloadditions. In order to control the stereochemical outcome of a reaction with a substoichiometric amount of a ligand-metal catalyst, it is desirable that a large rate acceleration is obtained in order to assure that the reaction only takes place in the sphere of the metal and the chiral ligand. The FMO considerations will be outlined in the following using nitrones as an example. 

Hydrocarbon Trap System. The concept of a hydrocarbon trap or adsorber system is based on molecular sieve hydrocarbon adsorber systems. The temperatures at which hydrocarbon adsorption takes place exist in the auto engine exhaust system during the period of cold start of an automobile when the catalytic control system has not yet reached functional temperature. Zeolites have been reportedly useful for hydrocarbon adsorption (53,169). Zeolites desorb hydrocarbons at temperatures of 400°C, ie, once the catalytic control system is functional. Therefore, hydrocarbons adsorbed by the zeolite can also be desorbed then oxidized by a catalyst. Methods to accomplish cold start hydrocarbon adsorption, heatup of the main catalyst, and desorption have been identified. Some of these systems use exhaust pipe valves to divert the exhaust gases to the hydrocarbon trap for the low temperature portion, and by-pass the gases around the trap after the main catalyst has heated up. One device that uses a heat exchanger is shown in Figure 15 (44). The Si—Al ratio in the zeolite is important, and by lowering the alumina content, the zeolite is rendered more hydrophobic and more able to adsorb... 

Catalytic Control of VOC Emissions, A. Cost Effective Viable Technology for Industrial, Commercial and Waste Processing Facilities, Manufacturers of Emission Controls Association, Washington, D.C., 1992. 

All the above species have been detected in various quantities at oxide surfaces. The discussion of this example serves mainly to show that catalytic reactions at oxide surfaces are very complex. This is a mixed blessing from the sensing point of view. It provides a broad spectrum of reactions that could be used. On the other hand, it can lead to great variation in the results obtained with only slightly different sensors. Another drawback of such a complex and diverse mechanism is the relatively slow time response which, in most cases, is limited by the rates of the chemical reactions (Fig. 8.10). Naturally, one tendency of the current research in this field is to increase the selectivity of the surface reactions by introducing additional catalytic control, for example, by incorporation of catalytic metals, metal clusters, and other surface modifiers. 

A highly enantioselective and diastereoselective addition of trisubstituted carbon donors, such as (166), to 2-chloroacrylonitrile (167), catalysed by bifunctional Cin- chona alkaloid catalysts, e.g. (169), has been reported as the first example of an asymmetric cascade that includes conjugate addition and protonation with efficient (g) catalytic control at two non-adjacent stereocentres (168).218... 

It will be always desirable to conduct C-H transformations under catalytic control to minimize the energy required and to maximize the selectivity of the reaction. Controlling the selectivity 16] is of paramount importance, because energy boundary conditions for all C-H transformations of simple alkane molecules are unfavorable. Table 3 reports, as a qualitative measure, heat of formation data... 

Recent work has focused on developing catalytically controlled asymmetric 1,3-dipolar cycloadditions of cyclic nitrones such as 2,3,4,5-tetrahydropyridine IV-oxide 174. The Lewis acid iron complex 181 catalyzes the cycloaddition of 2,3,4,5-tetrahydropyridine jV-oxide 174 with methacrolein to give (3A,5A)-isoxazolidine 182 in good yield and high enantiomeric selectivity (Scheme 48) <2002JA4968>. The same catalyst 181 however gave (3R,4A,5R)-isoxazolidine 183 with much lower selectivity when crotonaldehyde was used. 

Complete oxidation of hydrocarbons in air is a useful method for atmospheric purification, and has been sucessfully applied in automotive exhaust control. An important new area is the catalytic control of the emissions of volatile organic compounds (VOC) in a more general sense [1]. Many sources, low concentrations and wide temperature ranges can be involved. 

Since its introduction some two decades ago, catalytic control of exhaust emissions from automobiles has had remarkable success, and now over 200 million vehicles worldwide... 

H. G. Linde and L. W. Austin, Catalytic control of anisotropic silicon etching, Sensors Actuators A 49, 181, 1995. 

Anciaux, A. J., Demonceau, A., Hubert, A. J., Noels, A. F., Petiniot, N., Teyssie, P. Catalytic control of reactions of dipoles and carbenes an easy and efficient synthesis of cycioheptatrienes from aromatic compounds by an extension of Buchner s reaction. J. Chem. Soc.,... 

One of the early problems with catalytic control of automobile exhaust emissions was during the few minutes immediately after starting the engine when the cold catalytic systems did not function. This was solved by developing a porous zeolite which traps the unburned hydrocarbons while the catalysts are still cold [15]. Once the catalysts have warmed up, the zeolite canister also warms, releasing the trapped hydrocarbons to the catalytic systems to perform their important control reactions. 

The selectivity of the bis(ylide)nickel catalysts frequently favors the formation of linear macromolecules with unsaturated end groups. In this case the FTIR spectrum of a PE film of defined thickness shows almost exclusively methyl and vinyl end groups. Their presence in equal quantities proves linearity. An example for the catalytically controlled formation of linear, unbranched macromolecules is given in Eq. (12). 

Catalytic Control of Architecture and Properties of Butadiene Block Copolymers... 

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