Carbon dioxide catalytic reactions

The catalytic cycles for reduction of alkyl and atyl halides using Ni(o), Co(i) or Pd(o) species are interrupted by added carbon dioxide and reaction between the first formed carbon-metal bond and carbon dioxide yields an alkyl or aryl car-boxylate. These catalyses reactions have the advantage of occuriiig at lower cathode potentials than the direct processes summarised in Table 4.14. Mechanisms for the Ni(o) [240] and Pd(o) [241] catalysed processes have been established. Carbon dioxide inserts into the carbon-metal bond in an intermediate. Once the carboxy-late-metal species is formed, a further electron transfer step liberates the carboxy-late ion reforming the metallic complex catalyst. 

Heating the first-obtained product in a strong acid leads to the hydrolysis of the ester. The resulting (3-ketoacid loses carbon dioxide under reaction conditions the acetal hydrolyses also reveal the free aldehyde (106-6). Aldol condensation of this last intermediate in the presence of a base with readily available rhodanine (106-7) links the two fragments. The double bond in the first-formed product is then reduced catalytically to afford darglitazone (106-8) [117]. 

Carbon dioxide insertion reactions are potential intermediate steps in catalytic cycles leading to reduction of C02 or its incorporation into organic molecules. Analogies with carbon monoxide chemistry may be drawn, e.g., insertion reactions of carbon monoxide (20) play a key role in both the... 

The processes going on inside this ceramic catalytic converter include the reactions shown in the insert. Fragments of unburned hydrocarbons and carbon monoxide and nitric oxide molecules are converted to less noxious substances, such as nitrogen and carbon dioxide, by reactions at the surface of the catalyst. 

A significant rate enhancement for the C02 insertion process was noted in the presence of alkali metal counterions (Table I), even in the highly coordinating THF solvent. This rate acceleration was not, however, catalytic in alkali metal counterion, since the once formed carboxylate was observed to form a tight ion pair (76, 77) via its uncoordinated oxygen atom with the alkali metal ion, as evinced by infrared spectroscopy in the v(C02) region. That is, the counterion was consumed during the carbon dioxide insertion reaction. 

Musie G, Wei M, Subramaniam B et al (2001) Catalytic oxidations in carbon dioxide-based reaction media, including novel C02-expanded phases. Coord Chem Rev 219-221 789-820... 

The reaction order with respect to time was determined by the differential method. A fractional order (1.3) is obtained for the catalytic reaction on both doped samples. However, as in the case of the same reaction on pure oxides, the initial reaction rate does not depend upon the pressure of either reagent (order zero). Since these results are similar to those obtained on pure samples, NiO(200°) and NiO(250°), we believe that the order with respect to time is, as in the former case, apparent and that it results from the inhibition of surface sites by carbon dioxide, the reaction product. The slowest step of the reaction mechanism on doped oxides should occur, therefore, between adsorbed species. 

The synthesis of methanol from carbon monoxide/hydrogen mixtures is also achieved by a catalytic process according to the following stoichiometric equation (Kasem, 1979 Muetterties and Stein, 1979 Klier, 1984 Lee, 1990 Chadeesingh, 2011) or by way of a carbon dioxide/hydrogen reaction ... 

In the case of the catalytic destruction of ozone, the catalyst speeds up a reaction that we do not want to happen. Most of the time, however, catalysts are used to speed up reactions that we do want to happen. For example, your car most likely has a catalytic converter in its exhaust system. The catalytic converter contains a catalyst that converts exhaust pollutants (such as carbon monoxide) into less harmful substances (such as carbon dioxide). These reactions occur only with the help of a catalyst because they are too slow to occur otherwise. 

Takimoto M, Nakamura Y, Kimura K, Mori M (2004) Highly enantioselective catalytic carbon dioxide incorporation reaction nickel-catalyzed asymmetric carboxylative cycli-zation of bis-1,3-dienes. J Am Chem Soc 126 5956-5957... 

The complete assembly for carrying out the catalytic decomposition of acids into ketones is shown in Fig. Ill, 72, 1. The main part of the apparatus consists of a device for dropping the acid at constant rate into a combustion tube containing the catalyst (manganous oxide deposited upon pumice) and heated electrically to about 350° the reaction products are condensed by a double surface condenser and coUected in a flask (which may be cooled in ice, if necessary) a glass bubbler at the end of the apparatus indicates the rate of decomposition (evolution of carbon dioxide). The furnace may be a commercial cylindrical furnace, about 70 cm. in length, but it is excellent practice, and certainly very much cheaper, to construct it from simple materials. 

Other components in the feed gas may react with and degrade the amine solution. Many of these latter reactions can be reversed by appHcation of heat, as in a reclaimer. Some reaction products cannot be reclaimed, however. Thus to keep the concentration of these materials at an acceptable level, the solution must be purged and fresh amine added periodically. The principal sources of degradation products are the reactions with carbon dioxide, carbonyl sulfide, and carbon disulfide. In refineries, sour gas streams from vacuum distillation or from fluidized catalytic cracking (FCC) units can contain oxygen or sulfur dioxide which form heat-stable salts with the amine solution (see Fluidization Petroleum). 

Experience in air separation plant operations and other ciyogenic processing plants has shown that local freeze-out of impurities such as carbon dioxide can occur at concentrations well below the solubihty limit. For this reason, the carbon dioxide content of the feed gas sub-jec t to the minimum operating temperature is usually kept below 50 ppm. The amine process and the molecular sieve adsorption process are the most widely used methods for carbon dioxide removal. The amine process involves adsorption of the impurity by a lean aqueous organic amine solution. With sufficient amine recirculation rate, the carbon dioxide in the treated gas can be reduced to less than 25 ppm. Oxygen is removed by a catalytic reaction with hydrogen to form water. 

In catalytic incineration, organic contaminants are oxidized to carbon dioxide and water. A catalyst is used to initiate the combustion reaction, which occurs at a lower temperature than in thermal incineration. Catalytic incineration uses less fuel than the thermal method. Many commercial systems have removal efficiencies eater than 98%. 

Catalytic methanation is the reverse of the steam reforming reaction. Hydrogen reacts with carbon monoxide and carbon dioxide, converting them to methane. Methanation reactions are exothermic, and methane yield is favored at lower temperatures ... 

In general compounds with heteroatoms (N, O, S and P) are more amenable to fluorescence reactions" than pure hydrocarbons. Under the influence of the catalytic sorbents substances rich in Jt-electrons are formed, that conjugate to rigid reaction products that are fluorescent when appropriately excited. The formation of fluorescent derivatives is frequently encouraged by gassing with nitrogen or carbon dioxide. 

These reactors contain suspended solid particles. A discontinuous gas phase is sparged into the reactor. Coal liquefaction is an example where the solid is consumed by the reaction. The three phases are hydrogen, a hydrocarbon-solvent/ product mixture, and solid coal. Microbial cells immobilized on a particulate substrate are an example of a three-phase system where the slurried phase is catalytic. The liquid phase is water that contains the organic substrate. The gas phase supplies oxygen and removes carbon dioxide. The solid phase consists of microbial cells grown on the surface of a nonconsumable solid such as activated carbon. 

Fig. 3 showed the catalyst stability of Ni-Mg/HY, Ni-Mn/HY, and Ni/HY catalysts in the methme reforming with carbon dioxide at 700°C. Nickel and promoter contents were fixed at 13 wt.% and 5 wt.%, respectively. Initial activities over M/HY and metal-promoted Ni/HY catalysts were almost the same. It is noticeable that the addition of Mn and Mg to the Ni/HY catalyst remarkably stabilized the catalyst praformance and retarded the catalyst deactivation. Especially, the Ni-Mg/HY catalyst showed methane and carbon dioxide conversions more thrm ca. 85% and 80%, respectively, without significant deactivation even after the 72 h catalytic reaction. 

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