Ethylene current-potential behavior

The complexity of the reaction rate transients, which consist of one fast and one slow stage, is in agreement with the cyclic voltammetric evidence abont the existence of differently accessible regions for surface charging. The first rapid step (a) is believed to be dne to accumulation of promoting species over the gas-exposed catalyst surface by the mechanism of backspillover, while the second step (b) is due to current-assisted chemical surface modification. Since no correlation between potential transients and reaction rate transients was manifested, a dynamic approach is justified and the applied current —rather than the catalyst overpotential— may be an appropriate parameter to describe the transient behavior of ethylene combustion rate at electrochemically promoted Ir02AfSZ film catalysts. For the interpretation of the fast transient steps (a) and (c), a dynamic model of electrochemical promotion has been developed, as presented in detail in Section 11.3. 

The galvanostatic-transient behavior of the catalyst potential and that of the reaction rate due to anodic current steps, was investigated as a function of the applied current. The reaction was the combustion of ethylene at 375°C over Ir02A SZ catalyst at highly oxidative feed conditions (C2H4 Oj = 1 100). Transients under current application (termed polarization) and after current interruption (relaxation) were recorded. In order to achieve well-established steady-states, long polarization of at least 100 min and relaxation of at least 200 min were applied. 

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