Nitrogen species concentration variations

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Fig. 2 depicts the variation of conversion and selectivity with the V/Mo ratio. The conversion of propane increased with V-loading, which is in agreement with previous reports indicating the role of V-sites in alkane activation [11]. However, the selectivity in acrylonitrile had a maximum for a V/Mo ratio of 0.3. This is also in agreement with literature data [11]. An excess of vanadium has been described as detrimental for the ammoxidation of propane because it promotes the conversion of ammonia to nitrogen and decreases the concentration of surface nitrogen species required for the acrylonitrile formation... 

Figure 25a shows the steady state production rate of C02 calculated for various CO pressures. We recognize the typical volcano shape observed in the experiments. The temperature corresponding to the maximum rate is very close to the experimental values. Figure 25b displays the variation of the coverage of the adsorbed species as a function of temperature for a NO pressure of 5 x 10-8 Torr and the same equivalent pressure in the CO beam. The nitrogen coverage is not represented because it remains very low due to the small barrier for associative desorption of N2. At low temperature, the concentration... 

Slight variations in the definition of reaction order may be found in the literature. For example, for some reactions there may be reason to believe that one species (for example, nitrogen) is inert, in the sense that changes in its concentration do not influence the rate of the reaction at constant pressure, and in such cases rij may be defined by considering simultaneous changes in the concentrations of species j and of the inert, with the total pressure held constant. In general, the resulting value of rij diflers from that defined above therefore it is important to ascertain the specific definition employed. An empirical formula that is often useful—for example, in the presence of an inert—is... 

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