Influence of oxide precursor

The reduction performance of catalyst is closely related with the composition of its precursor in hydrogen flow. As mentioned earlier, this is due to the different reduction mechanisms for catalysts with different precursors. All precursors of iron oxide such as Fe304, Fei xO and their mixture are possible for fused iron catalysts, while the sequence of the reduction rate as well as the reduction temperature is Fei xO Fe304 mixture. Apparently, the catalysts with non-stoichiometric Fei xO with wiistite structure as precursors have the fastest reduction rate and the lowest reduction temperature. As mentioned before, the defects of iron ions in lattice of Fei xO has serious impact on its reduction properties. It can be seen from Fig. 5.13 that the reduction process is faster and more complete when the amount of the defects is larger in wiistite. 

Oxides Start temp./°C Terminal temp./°C Temp, of max. reduction rate/°C Reduction rate/(x 10 mg- min ) Reduction degree/% 

Note Heating rate 3°C min H2 flow rate 175ml-min instrument Shimazi TGA-41. 

The author s research results show that when the catalyst precursor is composed by two different phases, such as FeO and Fe304, two peaks appear on the DTG curve obtained from reduction by H2, which correspond to the reduction of Fei xO and Fc304, respectively (Table 5.10). It indicates that the reduction process is followed by the reduction of phase by phase in turn, and belongs to the competitive mechanism. The easily reduced FeO is first reduced to a-Fe, and then the reduction of Fc304 starts. The result of phased reduction is that the reduction rate of the catalyst is decreased, while the reduction temperature is increased, and also the activity of catalyst after reduction is decreased. 

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