AVS 46th International Symposium
    Surface Science Division Thursday Sessions
       Session SS3+AS+NS-ThM

Paper SS3+AS+NS-ThM11
Investigations of Surface Reactions on Thin Film-Supported Catalysts Using Microhotplate Arrays

Thursday, October 28, 1999, 11:40 am, Room 604

Session: Novel Surface Probes & Technique Enhancement
Presenter: S. Semancik, National Institute of Standards and Technology
Authors: R. Walton, National Institute of Standards and Technology
R. Cavicchi, National Institute of Standards and Technology
S. Semancik, National Institute of Standards and Technology
M. Class, National Institute of Standards and Technology
J. Allen, National Institute of Standards and Technology
J. Suehle, National Institute of Standards and Technology
Correspondent: Click to Email
This presentation describes the use of microhotplate arrays and electrical measurements for efficiently investigating surface reactions on supported metal catalysts under varied temperature and gas exposure conditions. Each ~100 µm x 100 µm microhotplate platform used in our work includes functionality for rapid control and measurement of film temperature (thermal time constant ~ 1 ms) and for probing of gas-induced changes in a film's electrical properties. Arrays of individually addressable microhotplates are well suited for directly comparing catalytic layers of different composition, loading, and degree of dispersion. The results we present are relevant to both gas sensing and catalysis. Specifically, four-element arrays were used to evaluate reactions on Pt, Pd, and Cu catalyst particles (formed by annealing 25-100 Å layers) supported on tin oxide. Electrical conductivity was used to monitor changes in the electron density of the thin film catalysts caused by surface reactions in air of H@sub 2@, CO and CH@sub 3@OH, respectively, at film temperatures ranging from 20 to 500 °C. Each of the catalysts interacts with these reactants in air to produce changes in film conductivity that we relate to factors including surface oxygen concentration, reaction rates, catalyst loading, and catalyst fouling. As a further example of this approach, we also illustrate the use of microhotplates to explore the conditions of thermal cycling and partial pressures under which CO oxidation oscillations occur on Pt particles supported on SnO@sub 2@.