Oxygen with carbonaceous compounds

The Reaction of Oxygen with Carbonaceous Compounds and Trace Mineral Constituents in an Inductive Electrodeless Discharge... 

Before measurement it must be decided exactly which isotopes are to be compared. For oxygen, it is usually the ratio of 0 to 0, and for hydrogen it is H to H. Such isotope ratios are measured by the mass spectrometer. For example, examination of a sample of a carbonaceous compound provides abundances of ions at two m/z values, one related to C and one to C (it could be at m/z 45 and COj at m/z 44). By convention, the heavier isotope is always compared with the lighter isotope. The ratio of isotopes is given the symbol R (Figure 48.1). 

The necessity for regeneration arises from the fact that catalyst activity declines with time on reaction, owing to small deposits of carbonaceous material and sulfur compounds on the catalyst. This deposit, of course, varies with feed stock, catalyst, and process conditions. The regeneration is carried out by oxidizing the deposits on the catalyst with a stream of air diluted to 2 to 3% oxygen with recycled flue gas. 

The shift toward lower reduction temperatures shows the improvement of the low temperature redox properties of the MnO/CeOj catalyst, which indicates the presence of metal-metal as well as metal-support interactions. These interactions are enhanced by the presence of CeO that induces the well-known spillover of hydrogen from Pt/and or Ag to CeOj or an increase in the oxygen mobility within CeO. The promoted catalysts showed higher activity than un-promoted one in the oxidation of phenol, and the amount of carbon deposit on them was small. For example, oxygen uptake by the combustion of carbonaceous compounds after the oxidation of phenol at 80°C for 1 h was 3535pmol/g-cat, 2660pmol/g-cat, and 2941 xmol/g-cat for MnO/CeOj, Pt-MnO /CeOj, and Ag-MnO/CeO, respectively. Larachi also promoted Mn/Ce composite oxide with lwt% of Pt [43]. 

Figure 1 shows the DTA curve obtained when a sample of diesel soot is burned in the absence of a catalyst. With increasing the temperature, four exothermic peaks appear. These peaks can be attributed to the combustion of different types of hydrocarbons constituting the soot (11). Indeed, it is known that a real soot consists of a volatile fraction, which is more active than a carbonaceous solid fraction. The composition of the volatile fraction can also vary depending on the quality of fuel and the engine s mode of operation. In some cases, aromatic, oxygenated and paraffinic compounds can be present, as well as residual coke of the lubricant (12). 

The oxidation process by the oxygen plasma and the etching process by the selfbias are effective in the SiOx deposition with less carbonaceous compounds. 

Numerous soot oxidation catalysts have been reported since the 1980s, because soot oxidation is fundamentally a simple complete oxidation reaction (carbonaceous compounds CO2 + H2O), so that sophisticated catalysts with high selectivity are not required. However, there is a critical problem in establishing contact and interaction, directly or indirectly, between the reactant (soot) and the catalyst, both of which are solid materials. Therefore, soot oxidation catalysts reported to date can be classified according to the assumed working mechanism that solves this problem. In this review the authors classify the catalysts into the four types shown in Fig. 2.5, based on the mediator for the oxidation reaction that connects the active sites of catalyst and soot surfaces mobile catalysts, mobile oxygen catalysts, NO2 mediating... 

Once a carbonaceous solid or liquid material is converted to a gaseous state, undesirable substances such as sulfur compounds and ash may be removed from the gas. In contrast to combustion processes, which work with excess air, gasification processes operate at substoichiometric conditions with the oxygen supply controlled (generally 35 percent of the... 

Carbon has been used in several forms. Activated charcoal found limited usage because of significant batch-to-batch variations. Kaiser (16) developed a carbonaceous material with pore structure similar to zeolites and referred to it as carbon molecular sieve. It is useful only for gases and very short chain compounds. It is unique in that it can be used for the analysis of oxygen, nitrogen, and carbon dioxide as shown in Figure 3.7. 

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