Low-temperature catalytic

Klingstedt, F., Arve, K., Eranen, K. and Murzin, D.Y. (2006) Toward improved catalytic low-temperature NOx removal in diesel-powered vehicles. Acc. Chem. Res., 39, 273-282. 

J. Rasko, G.A. Somoijai, and H. Heinemann. Catalytic Low-Temperature Oxyde-hydrogenation of Methane to Higher Hydrocarbons with Very High Selectivity at 8-12% Conversion. Appl. Catal. A 84 57 (1992). 

Contribution of Ions in the Subthreshoid Piasma Ignition of Hydrogen. Analyze the non-branching chain mechanism (11-25), (11-27), (11-28), (11-29) of the plasma-stimulated quasi-catalytic low-temperature oxidation of H2. Why does the conventional gas-phase oxidation of hydrogen have a threshold nature (explosion/no explosion see Section 11.2.3), whereas the quasi-catalytic chain mechanism (11-25), (11-27), (11-28), (11-29) is able to occur in a wide range of pressures and temperatures without any specific thresholds ... 

Catalytic Low temperature gelling below 400°C ensures a porous... 

Dark body radiator (A > 3 pm) e. g., electric dark body radiators made of thin steel tubes with internal electric heaters and reflectors made of aluminum or ceramics, catalytic low temperature radiators using a catalytic reaction of gaseous fuel below the ignition point as a radiation source, gas-heated metal walls in the temperature range 500-800 °C or ceramic plates with temperatures up to about 1100°C... 

Many other catalytic fluidized-bed processes have been tested at various scales. These include catalytic low-temperature oxidation, catalytic gasification and pyrolysis of biomass and waste plastic, production of carbon nanotubes, dry reforming of methane, hydrogenation and dehydrogenation of hydrocarbons, methanol-to-gasoline (MTC) process, synthesis of dimethyl ether (DME), and selective catalytic reduction of nitrogen... 

Hexafluoiopiopylene and tetiafluoioethylene aie copolymerized, with trichloiacetyl peroxide as the catalyst, at low temperature (43). Newer catalytic methods, including irradiation, achieve copolymerization at different temperatures (44,45). Aqueous and nonaqueous dispersion polymerizations appear to be the most convenient routes to commercial production (1,46—50). The polymerization conditions are similar to those of TFE homopolymer dispersion polymerization. The copolymer of HFP—TFE is a random copolymer that is, HFP units add to the growing chains at random intervals. The optimal composition of the copolymer requires that the mechanical properties are retained in the usable range and that the melt viscosity is low enough for easy melt processing. 

Thermochemical Liquefaction. Most of the research done since 1970 on the direct thermochemical Hquefaction of biomass has been concentrated on the use of various pyrolytic techniques for the production of Hquid fuels and fuel components (96,112,125,166,167). Some of the techniques investigated are entrained-flow pyrolysis, vacuum pyrolysis, rapid and flash pyrolysis, ultrafast pyrolysis in vortex reactors, fluid-bed pyrolysis, low temperature pyrolysis at long reaction times, and updraft fixed-bed pyrolysis. Other research has been done to develop low cost, upgrading methods to convert the complex mixtures formed on pyrolysis of biomass to high quaHty transportation fuels, and to study Hquefaction at high pressures via solvolysis, steam—water treatment, catalytic hydrotreatment, and noncatalytic and catalytic treatment in aqueous systems. 

Any of the medium heat-value gases that consist of carbon monoxide and hydrogen (often called synthesis gas) can be converted to high heat-value gas by methanation (22), a low temperature catalytic process that combines carbon monoxide and hydrogen to form methane and water. 

Liquid Fuels. Liquid fuels can be obtained as by-products of low temperature carbonization by pyrolysis, solvent refining, or extraction and gasification followed by catalytic conversion of either the coal or the products from the coal. A continuing iaterest ia Hquid fuels has produced activity ia each of these areas (44—46). However, because cmde oil prices have historically remained below the price at which synthetic fuels can be produced, commercialization awaits an economic reversal. 

Low temperature filtration (qv) is a common final refining step to remove paraffin wax in order to lower the pour point of the oil (14). As an alternative to traditional filtration aided by a propane or methyl ethyl ketone solvent, catalytic hydrodewaxing cracks the wax molecules which are then removed as lower boiling products. Finished lubricating oils are then made by blending these refined stocks to the desired viscosity, followed by introducing additives needed to provide the required performance. Table 3 Usts properties of typical commercial petroleum oils. Methods for measuring these properties are available from the ASTM (10). 

A low temperature catalytic process has been reported (64). The process involves the divalent nickel- or zero-valent palladium-catalyzed self-condensation of halothiophenols in an alcohol solvent. The preferred halothiophenol is -bromothiophenol. The relatively poor solubiHty of PPS under the mild reaction conditions results in the synthesis of only low molecular weight PPS. An advantage afforded by the mild reaction conditions is that of making telecheHc PPS with functional groups that may not survive typical PPS polymerization conditions. 

These precursors are prepared by reaction of fuming nitric acid in excess acetic anhydride at low temperatures with 2-furancarboxaldehyde [98-01-1] (furfural) or its diacetate (16) followed by treatment of an intermediate 2-acetoxy-2,5-dihydrofuran [63848-92-0] with pyridine (17). This process has been improved by the use of concentrated nitric acid (18,19), as well as catalytic amounts of phosphoms pentoxide, trichloride, and oxychloride (20), and sulfuric acid (21). Orthophosphoric acid, -toluenesulfonic acid, arsenic acid, boric acid, and stibonic acid, among others are useful additives for the nitration of furfural with acetyl nitrate. Hydrolysis of 5-nitro-2-furancarboxyaldehyde diacetate [92-55-7] with aqueous mineral acids provides the aldehyde which is suitable for use without additional purification. 

Friedel-Crafts. 2-Phenylpropanol results from the catalytic (AlCl, FeCl, or TiCl reaction of ben2ene and propylene oxide at low temperature and under anhydrous conditions (see Friedel-CRAFTS reactions). Epoxide reaction with toluene gives a mixture of 0-, m- and -isomers (75,76). 

Chlorination with SO2CI2, which is favorable to the para isomer at the monochlotination stage, gives an excellent yield of 2,4-dichlorophenol. Startiag with (9-chlorophenol, it is possible to attain a selectivity for 2,4-dichlorophenol of 98%, if chlotination is carried out ia Hquid SO2 at low temperature (20). 2,6-Dichlorophenol is also used as an iatermediate. It is obtained by chlotinatiag o-chlorophenol ia the presence of a catalytic quantity of an amine, with or without a solvent medium (21,22), giving a yield of 90%. 

The precious metals possess much higher specific catalytic activity than do the base metals. In addition, base metal catalysts sinter upon exposure to the exhaust gas temperatures found in engine exhaust, thereby losing the catalytic performance needed for low temperature operation. Also, the base metals deactivate because of reactions with sulfur compounds at the low temperature end of auto exhaust. As a result, a base metal automobile exhaust... 

Product Quality Considerations of product quahty may require low holdup time and low-temperature operation to avoid thermal degradation. The low holdup time eliminates some types of evaporators, and some types are also eliminated because of poor heat-transfer charac teristics at low temperature. Product quality may also dic tate special materials of construction to avoid met hc contamination or a catalytic effect on decomposition of the product. Corrosion may also influence evaporator selection, since the advantages of evaporators having high heat-transfer coefficients are more apparent when expensive materials of construction are indicated. Corrosion and erosion are frequently more severe in evaporators than in other types of equipment because of the high hquid and vapor velocities used, the frequent presence of sohds in suspension, and the necessary concentration differences. 

At low temperatures unstable adsorption products or reaction intermediates could be trapped. Thus, carbonite CO, ions arise on CO interaction with basic oxygen ions which account for catalytic reaction of isotopic scrambling of CO or thiophene on activated CaO. 

The fluoride anion has a pronounced catalytic effect on the aldol reaction between enol silyl ethers and carbonyl compounds [13] This reacbon proceeds at low temperature under the influence of catalytic amounts (5-10 mol %) of tetra-butylammonium fluoride, giving the aldol silyl ethers in high yields (equation 11). 

Certain starting materials may give rise to the non-selective formation of regioisomeric enolates, leading to a mixture of isomeric products. Furthermore a ,/3-unsaturated carbonyl compounds tend to polymerize. The classical Michael procedure (i.e. polar solvent, catalytic amount of base) thus has some disadvantages, some of which can be avoided by use of preformed enolates. The CH-acidic carbonyl compound is converted to the corresponding enolate by treatment with an equimolar amount of a strong base, and in a second step the a ,/3-unsaturated carbonyl compound is added—often at low temperature. A similar procedure is applied for variants of the aldol reaction. 

The reaction takes place at low temperature (40-60 °C), without any solvent, in two (or more, up to four) well-mixed reactors in series. The pressure is sufficient to maintain the reactants in the liquid phase (no gas phase). Mixing and heat removal are ensured by an external circulation loop. The two components of the catalytic system are injected separately into this reaction loop with precise flow control. The residence time could be between 5 and 10 hours. At the output of the reaction section, the effluent containing the catalyst is chemically neutralized and the catalyst residue is separated from the products by aqueous washing. The catalyst components are not recycled. Unconverted olefin and inert hydrocarbons are separated from the octenes by distillation columns. The catalytic system is sensitive to impurities that can coordinate strongly to the nickel metal center or can react with the alkylaluminium derivative (polyunsaturated hydrocarbons and polar compounds such as water). 

The second method used to reduce exliaust emissions incorporates postcombustion devices in the form of soot and/or ceramic catalytic converters. Some catalysts currently employ zeolite-based hydrocarbon-trapping materials acting as molecular sieves that can adsorb hydrocarbons at low temperatures and release them at high temperatures, when the catalyst operates with higher efficiency. Advances have been made in soot reduction through adoption of soot filters that chemically convert CO and unburned hydrocarbons into harmless CO, and water vapor, while trapping carbon particles in their ceramic honeycomb walls. Both soot filters and diesel catalysts remove more than 80 percent of carbon particulates from the exliatist, and reduce by more than 90 percent emissions of CO and hydrocarbons. 

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