Fe2 MoC

Fig. 15. Deactivation of Fe2(MoQ4)3 and a mechanical mixture (50 50) of Fe2(Mo04>3 + a-Sb2C>4 during the oxidative dehydrogenation of ethanol to acetaldehyde. The amount of Fe2(MoC>4)3 is identical (200 mg) in both experiments. T = 350°C ethanol/02/N2 2/1/20. Gas flow rate 50 ml/min.

The first Raman spectra of bulk metal oxide catalysts were reported in 1971 by Leroy et al. (1971), who characterized the mixed metal oxide Fe2(MoC>4)3. In subsequent years, the Raman spectra of numerous pure and mixed bulk metal oxides were reported a summary in chronological order can be found in the 2002 review by Wachs (Wachs, 2002). Bulk metal oxide phases are readily observed by Raman spectroscopy, in both the unsupported and supported forms. Investigations of the effects of moisture on the molecular structures of supported transition metal oxides have provided insights into the structural dynamics of these catalysts. It is important to know the molecular states of a catalyst as they depend on the conditions, such as the reactive environment. 

Table 5 compares the results obtained with pure Fc2(Mo04)3 and the mixture at various O2/ETH ratio. The selectivity of the mixture is always higher than that of pure Fe2(MoC>4)3, but the conversions are very close (let us remind that the reactor contained the same total amount of Fe2(Mo04)3 in both cases, namely 200 mg.). 

For the run of long duration (30 hrs) it was observed that at first the conversion of pure Fe2(Mo04)3 is higher than that of the mixture but the former decreases more rapidly than the latter. After about 1.5 hrs, the conversion of pure Fc2(MoC>4)3 is lower than that of the mixture. The selectivity (and yield) of the mixture always remains higher than that of pure Fe2(Mo04)3. 

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