5524
J . Phys. Chem. 1989,93, 5524-5531
Electrode-Modlfled Zeoiltes: Electrode Microstructures Contained In and on a Heterogeneous Catalyst Debra R. Rolison,* E. A. Hayes, and W. E. Rudzinskit Code 61 70, Surface Chemistry Branch, Naval Research Laboratory, Washington, D.C. 20375-5000 (Received: April 15, 1988; In Final Form: February 9, 1989)
In this work, zeolitesupportedPt(0) microstructures sized less than 10 nm are addressed as electrodesusing dispersion electrolysis. Modification of a heterogeneous catalyst with ultramicroelectrodespermits exploration of electrode processes in an interphase dominated by the nature of the heterogeneous catalyst and at electrode sizes where bulk metallic properties may not apply. The systems described are Pt supported on zeolite type Y and Pt supported on y-alumina. The electrolytic response of zeolite-supported Pt in the absence of added electrolyte salt for water or a benzene-water mixture is markedly more effective than that at alumina-supported Pt and is seen to depend on the size of the Pt particles supported on the exterior of the zeolite surface. Both supported systems behave as ultramicroelectrodesin that electrolysis is sustained in their presence under conditions that are strictly Ohmic for the feeder electrodes due to the high resistivity of the medium in the absence of electrolyte salt. X-ray photoelectron spectroscopic measurements confirm the expected low concentration and the metallic form of Pt on the zeolite exterior and indicate the approximate particle size of the supported Pt. A particle size effect for the electrolysis of water was observed for Pt supported on zeolite. The conductivity of a dispersion containing water and zeolite is shown to be greater than that derived from ions generated by zeolite-promoted autoprotolysis of the water. Zeolite, thus, offers a solid-state ionic environment that effectively contributes to the ionic strength of the dispersion without requiring dissolution of an electrolyte salt. Experiments with variously sized electroactivesolutes demonstrated that, under the low-field conditions (
