Combustion cation effects

Cationic Effects During Lignite Pyrolysis and Combustion... 

We are being somewhat disingenuous here. If performed and interpreted correctly and with the appropriate ancillary phase-change enthalpy information, the enthalpy of formation of an arbitrary species by ion-molecule reaction chemistry and by combustion calorimetry must be the same. That the ionization potential of quinuclidine is higher than l,4-diazabicyclo[2.2.2]octane simply says that there is a stabilizing effect in the radical cation of the latter not found in the former. This information does not say that there is a stabilizing effect in the neutral molecular form of the latter not found in the former. After all, we trust the reader is not bothered by the fact that the ionization potential order of the cyclohexenes increases in the order 1,3-diene < 1,4-diene < 1-ene < 1,3,5-triene (benzene). 

However, the extent of the activity enhancement cannot be related to the higher surface area of this material. Two possible explanations were proposed to account for the effect of mirror plane composition on combustion activity one is related to the different oxidation state of the cation in the mirror plane the other is associated with the crystal structure of layered-alumina materials (i.e., magne-toplumbite and (3-Al203) which have different population and co-ordination of the ions in the mirror planes. Both these electronic and structural factors can, in principle, affect the redox properties. 

Collagen, human body, 132-133 Combustion flame-chemical vapor condensation (CF-CVC) nanostructured materials, 10-11 schematic, 10 7T-Complexation sorbents description, 108-109 effects of cation, anion, and substrate, 112-113... 

Moljord et al [12] have shown, for protonic Y zeolites, that density of acid sites is the most important fector in determining the rate of coke oxidation and that the larger the number of Al atoms or protonic acid sites per unit cell, the easier the coke combustion. This was not observed in the present work, since coke formed on USY (high acid sites density) was more difficult to bum than that formed on CREY-2 (low acid sites density). Although the role of rare earth cations in coke combustion has yet to be further explored, this observation suggests that these cations present a catalytic effect on promoting coke oxidation. 

Experiments have shown that small amounts of certain metals can accelerate the rate of char combustion (4 9). A number of anions and cations have been shown to accelerate the combustion of carbons at concentrations of 10 to 1000 ppm. Table II shows the relative influence on the combustion rate of various salts added as solutions to purified graphite. Relatively small amounts of metals can accelerate the rate of combustion by many orders of magnitude. To effectively catalyze the combustion rate of coal, the metal which accelerates the rate must be distributed on nearly the molecular level, and be present in sufficient concentration to accelerate the rate. The range of relative acceleration of the combustion rate by different metals is shown in Figure 3. These estimates are made... 

Monophasic Ln x MnOs (Ln = La, Nd) perovskites with high surface areas (8-27 m /g) were synthesised at mild conditions by the freeze-drying method, and were found to be active for the catalytic combustion of ethane at low temperatures (573 to 648 K). As a general troid, the substitution of the rare earth cation by potassium decreased the intrinsic activity, reduced the reaction order in oxygen and, for the more substituted samples (x>0.10), it increased the selectivity to ethene. It was found that the rare earth cation also influenced the catafytic activity of the substituted perovskites. These effects were analysed in terms of structural modifications induced by the introduction of potassium in the perovskites. 

The effect of the cation in the A-poshion can be more clearly seen in Fig. 5, in which the areal rates of ethane transformation as a function of x are conq)ared. The activity of the unsubstituted sanqrles was very similar, being sU tly higher for the La catalyst. By contrast, the ethane combustion rate was higher on the substituted Ndi-xKxMnOa perovskites as con ared with the homologous Lai-xKxMnOs samples with the same substitution level. This reveals that the nature of the rare-earth cation also has a significant effect in the catalytic performance, especially in the presence ofpotassiiun. 

Effects of the small amount of additives to Pd-SAPO-5 on the activity for CH4 combustion were further studied (Table 11). It was clearly shown in Table 11 that the combination of the small amounts of metal cations with Pd was effective for increasing the CH4 oxidation activity in the low-temperature range below 673 K. However, the temperature for 90 percent CH4 combustion was elevated by the addition of metal cations. It is reported that the addition of a small amount of metal oxide to Pd increases the surface... 

Lean NOx-SCR with CH4 has been investigated on Co-modified synthetic ferrierite prepared in different conditions of ion exchange (temperature, time, precursor zeolite composition), A maximum NOx conversion (50% at 100% CH4 conversion) was obtained at 500°C. Activity and selectivity depend on the nature of Co species (from mononuclear to polynuclear cationic to oxidised phases) formed into ferrierite. The effect of side reactions such as uncatalysed and catalysed methane combustion on catalytic performance is discussed. 

Selectivities better than those obtained with iron have been achieved in the Pf -catalyzed oxidation of methane by O2 [28], Here, methane is activated by bare Pf to afford the PtCH2 cation in the first step Reaction 10). The subsequent oxidation Reactions 11 a and 11 b occur in a 3 7 ratio. Because PtO" continues to activate methane Reaction 12), Pt and PtCHj cations are effectively regenerated, thus giving rise to one of the rare examples of genuine catalytic cycles in the gas phase nevertheless, side reactions limit the turnover number to ca. 6. Instructive in this context is the observation [29] that the putative neutral products of Reaction 11, i.e., formaldehyde and formic acid, efficiently react with PP as well as PtO", eventually leading to CO2 and H2O. Thus, combustion rather than partial oxidation of methane takes place if no particular precautions are applied. 

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