New understanding of defect mechanisms in oxidation catalysis from dynamic electron microscopy

2 New understanding of defect mechanisms in oxidation catalysis from dynamic electron microscopy 

Here we present thermodynamic discussions and developments based on recent in situ ETEM studies. These are important in predicting the enthalpy of formation of vacancies in oxide catalysts, the probability for CS planes to form and catalyst performance. They are also important in the design of new or improved oxide catalysts. 

From the in situ reduction studies described in previous sections, it is clear that non-stoichiometry in an oxide catalyst results from the loss of the catalyst s 

More generally, co is independent of the external gas pressure k is the Boltzmann constant (1.38 x 10 erg deg ) and T is the temperature in Kelvin. Furthermore, the equilibrium between co and a collapsed CS plane fault is maintained by exchange at dislocations bounding the CS planes. Clearly, this equilibrium cannot be maintained except by the nucleation of a dislocation loop and such a process requires a supersaturation of vacancies and CS planes eliminate supersaturation of anion vacancies (Gai 1981, Gai et al 1982). Thus we introduce the concept of supersaturation of oxygen point defects in the reacting catalytic oxides, which contributes to the driving force for the nucleation of CS planes. From thermodynamics. 

Using the values for -AH and Ls (Kubaschevski and Evans 1962), we can estimate that for M0O3, AHy 0.4 eV 0.1 eV. AHy is low for M0O3, which means that it is easy to remove anions from its lattice to form vacancies. 

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