In Situ Controlled Promotion of Catalyst Surfaces via Solid Electrolytes: Ethylene Oxidation on Rh and Propylene Oxidation on Pt

The kinetics of C(2)H(4) oxidation on Rh and C(3)H(6) oxidation on Pt were investigated on polycrystalline metal films interfaced with ZrO(2)(8mol%Y(2)O(3)) solid electrolyte in galvanic cells of the type: C(2)H(4), O(2), Rh / YSZ / Pt, O(2) and C(3)H(6), O(2), CO(2), Pt / YSZ / Au, C(3)H(6), O(2), CO(2) It was found that by applying positive potentials and thus, supplying O(2-) to the catalyst surface, up to 100-fold increases in catalytic rate can be obtained (electrophobic NEMCA effect) for the case of C(2)H(4) oxidation on Rh. For the case of C(3)H(6) oxidation on Pt, up to 6-fold increases in catalytic rate were observed by negative potentials, i.e. removing of O(2-) from the catalyst surface (electrophilic NEMCA effect). The induced changes in catalytic rates for both reactions were found to be 10(3) to 5x10(4) higher than the rates of ion transfer to or from the catalyst-electrode surface. For both reactions it was found that varying the catalyst potential, and thus work function, causes pronounced changes in activation energy and preexponential factor, leading to an interesting demonstration of the well-known "compensation" effect. The results can be rationalized on the basis of the theoretical considerations invoked to explain previous NEMCA studies, i.e. the effect of changing work function on chemisorptive bond strengths of electron acceptor and electron donor adsorbates.