SUPPORT-INDUCED PROMOTIONAL EFFECTS ON THE ACTIVITY OF AUTOMOTIVE EXHAUST CATALYSTS - 1 - THE CASE OF OXIDATION OF LIGHT-HYDROCARBONS (C2H4)

The kinetics of oxidation of a light hydrocarbon (C2H4) were studied o n catalysts comprising of combinations of one of three metals, Pt, Pd or Ph supported on five different supports, that is SiO2, gamma-Al2O3, ZrO2 (8% Y2O3), TiO2 or TiO2 (W6+) Significant variation of turnover frequency with the carrier was observed, which cannot be explained by structure sensitivity considerations and is attributed to interactions between the metal crystallites and the carrier. The catalytic activit y of these metal-support combinations was investigated over a wide ran ge of partial pressures of ethylene and oxygen. In a separate set of e xperiments, the kinetics of C2H4 oxidation were also investigated on p olycrystalline Ph films interfaced with ZrO2 (8 mol% Y2O3) solid elect rolyte in a galvanic cell of the type: C2H4, O-2, Rh/YSZ/Pt, air, duri ng regular open-circuit conditions as well as under Non-Faradic Electr ochemical Modification of Catalytic Activity (NEMCA), that is, closed- circuit conditions. Up to 100-fold increase in catalytic activity was observed by supplying O(2-)ions to the catalyst surface via positive p otential application to the catalyst. The observed kinetic behavior up on increasing catalyst potential parallels qualitatively the observed alteration of turnover frequency with variation of the support of the Rh crystallites. (C) 1997 Elsevier Science B.V.