AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP25
A Double Quartz Crystal Microbalance Sensor for Monitoring High Pressure Heterogeneous Catalytic Reactions on Real Catalysts

Tuesday, October 3, 2000, 5:30 pm, Room Exhibit Hall C & D

Session: Poster Session
Presenter: I. Zori@aa c@, Chalmers University of Technology and Göteborgs University, Sweden
Authors: I. Zori@aa c@, Chalmers University of Technology and Göteborgs University, Sweden
P. Borchardt, Chalmers University of Technology, Sweden
C. Keller, Chalmers University of Technology, Sweden
B. Kasemo, Chalmers University of Technology, Sweden
Correspondent: Click to Email
The quartz crystal microbalance (QCM) is a piezoelectric oscillator with a high sensitivity for micro weighing (<0.01ML of H@sub 2@) and a fast response. In this work we report a novel sensor consisting of two QCMs mounted on a single, 5 MHz, AT cut quartz crystal. The catalyst consists of metallic, highly dispersed, nanosized Pt particles on an Al@sub 2@O@sub 3@ washcoat deposited on one QCM by standard wet deposition methods. The other QCM, coated with washcoat only, was used as a reference allowing for subtraction of the frequency shift due to temperature changes, or in a constant temperature experiment, the separation of gases adsorbed on the noble metal of the catalyst from those adsorbed on the alumina support. The catalytic reaction chosen for testing of the sensor system was the high pressure H@sub 2@+O@sub 2@ reaction, catalyzed by nanosized Pt particles on alumina support. The resonant frequencies of the two QCMs, proportional to the total coverage of the reactants, were monitored. The time dependence of the frequency difference (proportional to the total coverage) reflects reaction kinetics on the Pt particles. These measurements are complemented by mass spectrometric measurements of the gas phase products, yielding wealthy information about reaction kinetics on a real catalyst at high pressure. In addition we also demonstrate the ability of the sensor for detection of kinetic phase transitions in the above reaction. The sensitivity of the sensor is estimated to about 30Hz/10@super 15@ Pt atoms. The noise level is < 1Hz thus enabling us to measure coverage changes corresponding to 2-3% ML.