Reduction by an Oxidizable Compound

The capability of the perovskite powders to reversibly deliver and pick up oxygen is in most cases evaluated by successive reduction-oxidation steps in laboratory-scale fixed bed reactors. The main reason for using fixed bed reactors is that it is possible to evaluate different compositions using only a small amoimt of active material and still determine the selectivity toward H2 and CO. 

In Table 37.1, the work presented thus far on the subject has been summarized and compared. There exist a very large number of articles concerning the partial oxidation of methane with perovskites however, presenting all of them is outside the scope of this chapter. Only articles that use for the oxidization of the reduced perovskite not air but other reducible compounds, such as H2O and 

3 Oxygen loss and uptake over Lao SroaFeOs, during oxidation with air, Fi20, and 

aiming at the production of valuable products such as H2 and CO are included. It is not easy to form a uniform basis to compare the results since each researcher has performed different experiments and reports the results by using different quantities. Furthermore, in many cases important information is not reported, for example, the degree of conversion of water during the solid oxidation step. 

Ryden et al. [36] were the first to test perovskite materials for CLR. They found that La,j,Sri j,Fe03 5 perovskites provided very high selectivity toward CO/H2 and should be well suited for CLR. Substituting La for Sr was found to increase the oxygen capacity of these materials, but reduced the selectivity toward CO/H2 and the reactivity with CH4. Lao.sSro.sFeo.sCoo.sOs- was found to be feasible for chemical looping combustion applications. 

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