Carbon monoxide, correlations with lead

The success of the correlation of catalytic behavior with bulk Mossbauer parameters by Skalkina et al. is also reflected in the work of Tops0e and Boudart (96). As discussed earlier, these authors found a decrease in the isomer shift of the octahedral iron ions in a lead-promoted Cr-Fe304 carbon monoxide shift catalyst, indicative of an increased covalency of these ions. Schwab et al. (203) have proposed a correlation of the activity for CO oxidation by ferrites with the octahedral ions in these materials, and the electron transfer required for this catalytic process may be facilitated by an increased covalency of the metal ions (204). In view of these suggestions, the lead-promoted catalyst is expected to possess a higher catalytic activity for the CO shift reaction than an unpromoted catalyst, as evidenced by the Mossbauer parameters of these two samples. This has in fact been shown experimentally to be the case (96). For the reverse CO shift reaction over supported europium (176), the success of the correlation between catalytic activity and the Mossbauer parameters (in this case the reducibility) has already been noted in Section III, A, 4. 

Fig. 9.1 The (valence) molecular orbitals of ethenedione. For the correlations with the MOs of carbon monoxide only one set of CO orbitals is shown thus for example MO 1 actually results from [0(2s)+C(2s)] + [0(2s)+C(2s)], and M02 results from [0(2s)+C(2s)] - [0(2s)+C(2s)]. These AMI MO energies are very approximate. For the construction of such MO diagrams see [55] Unlike the case of 2 CO, bringing two CH2 groups together does not lead to a triplet because CHj lacks degenerate orbitals and thus so does ethene [55]...

The oxygen sorption capacities of the four catalysts vary in a broad range. They cannot be correlated with the carbon monoxide sorption capacities, independent of the fact whether the latter are related to the catalyst mass or to the platinum mass. No explanation could be found for the comparatively low oxygen sorption capacity of the catalyst prepared by use of the cordierite carrier (cat. 1). The results obtained with the two catalysts prepared using a-AljOs carriers (cat. 2 and cat. 3) clearly indicate that a prolonged calcination leads to both a diminuation of the tin(IV)oxide surface area and a lower oxygen sorption capacity while the platinum dispersion obtained is not markedly influenced. 

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