Carbonaceous compounds, reaction

Because molecular graphics suggested that isomerization of decene intermediates could not occur entirely inside the TON channels, it was theorized that this reaction occurred at the mouth of the micropores. This pore-mouth catalysis was confirmed by characterization of Pt TON samples recovered after various time-on-stream (TOS). The quasi-immediate retention of 1.5-2.0 wt % of carbonaceous compounds on the catalysts could be observed, these compounds causing a quasi-total blockage of the access of nitrogen (hence, of reactants) to the TON... 

Carbonaceous compounds can also form in the absence of a catalyst by free-radical, gas-phase condensation reactions. The formation of this pyrolytic carbon is known in steam-reforming reactors where it can be controlled to some extent by minimizing the free volume within the reactor chamber. This type of carbon does not form readily with methane but can be severe with larger hydrocarbons. The compounds formed by free-radical reactions tend to be quite different from the graphitic carbon formed by metal catalysts. For example, Lee et al. showed that the compounds formed by passing pure, undi-... 

Carbonaceous compounds have the peculiarity of being nondesorbed products.178,791 Therefore, their formation, besides reaction steps, requires the molecules to be retained either within the pores or on the outer surface of the molecular sieve. 

Both reasons can also play a role in the retention of carbonaceous compounds formed during the transformation of functionalized reactants. However, in both cases, there is an additional effect due to the polarity of these carbonaceous compounds, which is often high. These compounds are therefore strongly adsorbed, limiting the access of reactant molecules to the pores and to the active sites and causing consequently a decrease in the reaction rate. The more polar (hydrophilic) the zeolite, the more significant this effect (as shown in Section 2.2.4 for the arene... 

There have been other recent papers on the reactions discussed in Section III.B.l and III.B.2. Provencher and McKenney [414,415] have further investigated the complex excitation of CN which occurs when small quantities of carbonaceous compound are added to active nitrogen. One of their main proposals is that CN(B2Ef) is excited by transfer of energy from vibrationally excited N2 rather than from a metastable, electronically excited molecule, as implied in reaction (79). However, it seems difficult to reconcile the large rate constant which they estimate for this process with the comparative inefficiency of N2 in quenching CN(fi2Et) [416,417], Recent experiments [418, 419] do appear to have confirmed that reaction (87) does excite CO to emit chemiluminescence in the vacuum ultraviolet. The overall rate constant for the... 

Differences observed in the number of carbon atoms, in the extent of branching and in the chemical nature of carbonaceous compounds trapped in the zeolite pores result mainly from differences in size of the cavities (or of the channel intersections) and from the differences in the strength or in the density of the acid sites. Indeed, differences in pore structure combined with differences in acidity affect the rate of the main reaction (oligomerization) relative to side... 

The decreasing trend for oxidation of C2H4 and CjHg in the presence of SOj was similar to that for NO conversion, regardless of the types of catdyst employed in this study. No activity loss by carbonaceous compounds deposited on the surface of the catalysts is anticipated during the course of reaction without SO,. 

Work on Mn/Ce composite oxide catalysts is abundant [31,34-41]. However, deactivation phenomenon is often observed, and deposition of carbonaceous compounds is the main cause for deactivation [31,35,38-40,42]. This situation is shown in Fig. 14. 5 for the oxidation of phenol the higher the reaction temperature, the faster the deposition of carbonaceous compounds [34]. 

In standard dehydration runs, 2 g of catalyst powder, preactivated by heating overnight at 550°C in air, were slurried in 10 g of HEP. The reaction was carried out at 160°C in a small glass batch stirred tank reactor, equipped with thermostating jacket. Activity was expressed as mol % overall conversion of HEP (Chep) or as mol % yield per gram of dry catalyst (Yvp), obtained after 4 h of reaction. Reactant and products were analysed by gas chromatography (GC). The composition of the carbonaceous compounds ( coke ) left behind on aged catalyst was determined as described elsewhere [11]. 

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

It is clear from Fig. 11.5.M that the mole fraction of the reactant A increases with time at a given bed depth, in other words, the conversion decreases. From Fig. ll.S.f-2 we see that the carbon is not deposited uniformly along the bed, but according to a descending profile. This is intuitively clear when the carbonaceous compound is deposited by a reaction parallel to the main, its rate of formation is maximum at the inlet of the reactor, where the mole fraction of the reactant is maximum. 

A possible process for the SiOx film deposition at low temperatures below 70°C may be a special plasma CVD method which involves some elimination of carbonaceous compounds. In the plasma CVD, we believe that SiOx films are formed in two reactions (1) the bond scission of Si-OC bond in TEOS to form Si or SiO radicals, and (2) the recombination between two radicals to form Si-O-Si linkage. The repetitious combination of the two reactions leads to the Si-O-Si network, and as a result, a SiOx film is deposited. On the other hand, fragments eliminated from TEOS, ethyl or ethoxy radicals, also are recombined to form carbonaceous compounds and incorporated into the SiOx film. In the conventional plasma CVD process, the carbonaceous compounds in the deposited SiOx film are eliminated by the pyrolysis of the SiOx film at high temperature (500 ) (2). Therefore, in the SiOx-deposition on the PET film surface, some special process for the elimination of the carbonaceous compounds instead of the pyrolysis treatment should be investigated. 

Atomic Composition of Deposited SiOx Films. We have investigated three processes for file elimination of carbonaceous compounds from the deposited SiOx films. The factors are (1) choice of silane compounds used as a starting material for the SiOx film deposition by the plasma CVD, (2) oxidation reactions by oxygen plasma and (3) etching reactions occurring near an electrode surface by the selfbias. 

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... 

Deposition of carbonaceous material is commonly encountered. These deposits can be formed by complex chemical reactions or they are simply formed by deposition of heavy compounds from the feed. It is rule rather than exception that the true character of a carbonaceous material is not known. Often, it is referred to as coke . 

The authors chose pyruvic acid as their model compound this C3 molecule plays a central role in the metabolism of living cells. It was recently synthesized for the first time under hydrothermal conditions (Cody et al., 2000). Hazen and Deamer carried out their experiments at pressures and temperatures similar to those in hydrothermal systems (but not chosen to simulate such systems). The non-enzymatic reactions, which took place in relatively concentrated aqueous solutions, were intended to identify the subsequent self-selection and self-organisation potential of prebiotic molecular species. A considerable series of complex organic molecules was tentatively identified, such as methoxy- or methyl-substituted methyl benzoates or 2, 3, 4-trimethyl-2-cyclopenten-l-one, to name only a few. In particular, polymerisation products of pyruvic acid, and products of consecutive reactions such as decarboxylation and cycloaddition, were observed the expected tar fraction was not found, but water-soluble components were found as well as a chloroform-soluble fraction. The latter showed similarities to chloroform-soluble compounds from the Murchison carbonaceous chondrite (Hazen and Deamer, 2007). 

The careful study of at least five different carbonaceous chondrites establishes the fact that these meteorites contain carbon compounds of extraterrestrial origin and of great significance in chemical evolution. Their presence confirms that the chemical reaction paths producing biologically important monomer molecules occur in the far reaches of our solar system. 

Diverse biomass compounds were heated in sealed autoclaves in the presence of acids as catalyst at 200 °C for 16 h, and essentially two kinds of reaction scenarios were found. For soft biomass, nontextured biomass, hydrophilic and water-dispersible carbonaceous nanoparticles in the size range of 20-200 nm were obtained. The occurrence as spherical particles indicates that the soft biomass was first liquefied, and then carbonized, which offers possibilities to chemically interfere with this complex process as discussed above. 

Investigators have used the words carbon and soot to describe a wide variety of carbonaceous solid materials, many of which contain appreciable amounts of hydrogen as well as other elements and compounds that may have been present in the original hydrocarbon fuel. The properties of the solids change markedly with the conditions of formation and, indeed, several quite well-defined varieties of solid carbon may be distinguished. One of the most obvious and important differences depends on how the carbon is formed carbon may be formed by a homogeneous vapor-phase reaction it may be deposited on a solid surface that is present in or near the reaction zone or it may be generated by a liquid-phase pyrolysis. 

In a further effort to identify the active intermediate that initiates the reaction, they tested the effect of a few possible ingredients on the production of EMC based on the knowledge about the chemical composition of the SEI on carbonaceous anodes. These model compounds included Li2C03, LiOCHs, and LiOH, while lithium alkyl carbonate was not tested due to its instability and therefore rare avail-ability. The results unequivocally showed that LiOCHs effectively catalyzes the ester exchange. 

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