HIGH-TEMPERATURE KELVIN PROBE FOR FLOW REACTOR STUDIES

A vibrating capacitor device (Kelvin probe) has been developed for measurements of work-function changes Delta Phi during ongoing catalytic reactions up to high temperatures (750 K) and atmospheric pressure. The construction is based on the piezoelectric actuator principle, and utilizes a lever arrangement that transfers the vibrating motion of the actuator to the reference electrode. The lever arrangement eliminates a static load on the actuator, which therefore allows a large distance between the actuator and the vibrating reference electrode. This makes possible much higher temperatures in the reaction/sample zone than the piezoelectric actuator itself permits. The large actuator-electrode distance also reduces the risk of electromagnetic pickup in the Delta Phi measurements, from the driving circuit for the piezoelectric actuator, The reference electrode is a gold disk with 3 mm diameter and a thickness of 0.1 mm. The practical Delta Phi resolution is presently about 5 meV. The device has been combined with on-line mass spectrometric detection of reaction rates and its performance is illustrated by results from the H-2/O-2 and CO/O-2 reactions on Pt. (C) 1995 American Institute of Physics.