Reactant gas composition

Three kinds of samples were prepared by varying reactant gas compositions. Whan nitrogen was added, the color of synthesized powder was change fiom white to jrellow and with increase of nitrogen content, it became more yellowish. From the color of synthesized powder, the nitrograi amtent in the sample can be estimate. 

Calculate the equilibrium CO concentration for the following reactant gas composition at 1 atm in the temperature interval between 373 and 773 K. 

Cell performance for any fuel cell is a function of pressure, temperature, reactant gas composition and fuel utilization. In addition, performance can be adversely affected by impurities in both the fuel and oxidant gases. 

Although CVD processes inherently involve rapid changes, it is useful to examine the limiting case of long reaction times for insights into the nature of the films that can be deposited. To do this, we examine the final equilibrium state for the reactions of interest, which will depend on the initial reactant gas composition and the final pressure and temperature. 

Figure 3. Relative amounts of solid carbon produced from 0C2H4 and QCO as a function of reactant gas composition and reaction time over iron pretreated in H2S/H2 = 1.1x10-5 at 600°C. ( Denotes behavior of unadulterated metal at steady state under same conditions).

No improvements of the light-off performance for Ce/Ab03 as a result of the pre-treatment or reactant gas composition can be observed (see Table 2). Obviously, ceria itself is a very poor oxidation catalyst. The light-off performance for C0/AI2O3 is, however, dramatically changed after pre-reduction at 550°C. The light-off temperatures (see Table 2) for CO and HC... 

The reactant-gas composition in the reactor is shown on the top of the diagram. Mass spectrometric intensities of ethane, carbon dioxides, and water (not shown) were monitored continuously as reactants were switched. At first, there was only 02 in the reactor. Both surface and lattice oxygen had label. When the reactants were switched to 1 02 and CH4, the surface oxygen state was rapidly populated by Fig. 7 shows that reaction of methane on this surface produces both ethane and carbon dioxide. The oxygen of the carbon dioxides, however, is mainly (87% and 13% O), i.e. the surface/gas-... 

Transient response experiments were conducted using a fixed-bed reactor which was equipped with 2 lines of reactant stream, which could be switched by use of a 4-way valve to change immediately one reactant gas composition to another. All dead volume was minimized. Effluent gases were stored in a multiposition 8-way loop valve, and analyzed in turn by means of on line gas chromatography. The first reaction run before switching the reactant gas will be called "Reaction A" and the latter run "Reaction B". 

Figure 4. Arrhenius plots of pure and supported La gSrQ 2Mn03. (LSM). Reactant gas composition 1% CH4, 4% O2, He (balance) sample weight 0.1 g, GHSV 135 000 h heating rate 10 K/min.

In a fuel cell, the difference in reactant gas compositions at the two electrodes leads to the formation of a difference in Galvani potential between anode and cathode, as discussed in the section Electromotive Force. Thereby, the Gibbs energy AG of the net fuel cell reaction is transformed directly into electrical work. Under ideal operation, with no parasitic heat loss of kinetic and transport processes involved, the reaction Gibbs energy can be converted completely into electrical energy, leading to the theoretical thermodynamic efficiency of the cell. 

Cell performance for any fuel cell is a function of pressure, temperature, reactant gas composition and utilisation. It is well known that an increase in the cell operating pressure enhances the performance of all fuel cells, including PAFCs. It was shown in Chapter 2, Section 2.5.4, that for a reversible fuel cell the increase in voltage resulting from a change in system pressure from Pi to P2 is given by the formula... 

In recapitulating the preceding discussion, for a given geometry and reactant gas composition, if we know the surface concentration of the reactant and product gas we can calculate the net flux of gaseous reactant to the solid surface. 

In experiments on the reaction of single particles, care is usually taken to maintain the reactant gas composition at a constant level in the bulk, i.e., to avoid starvation. For such systems the overall driving force is clearly defined and the rate controlling step or the appropriate asymptotic regime is readily identified. 

It is to be stressed to the reader that even in this context reactivity is a qualitative concept in general, one would determine the reactivity by evaluating the fractional reaction (i.e., weight loss) of a coal particle for certain standard conditions, such as temperature, pressure, and reactant gas composition. A great deal more work has to be done in this area to make the concept of coal reactivity quantitative. 

The SCR activity measurements were carried out on cmshed samples sieved to obtain fractions of 0.18-0.300 mm. These measurements were carried out in a fixed-bed reactor, with 10 mg of the catalyst loaded between two layers of inert quartz wool. The reactant gas composition was 1000 ppm NO, 1100 ppm NH3, 3.5% O2, 2.3% H2O and He balance. The total flow rate was 300 mL/min (ambient conditions), with a continuous monitoring of the NO and NH3 concentration with a Thermo Electron model 17C chemiluminescent NO-NOx gas analyser. The catalytic activity, represented as a first-order rate constant (k), can be calculated from the NO conversion, X, as Eq. 2 ... 

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