Infrared emission study of the CO/O2 reaction over a Pd/SiO2 catalyst. Temperature inhomogeneities within the catalyst

Abstract

Infrared emission measurements have been made from a Pd/SiO₂ catalyst when flowing streams of CO/O₂ reagents pass over the catalyst at various temperatures. At higher catalyst temperatures as measured by a thermocouple the reaction enters into a self-heating regime where the black-body emission observed was much greater than that expected from the measured temperatures of the catalyst. This is accounted for in terms of the metal particles of the catalyst being much hotter than the silica matrix, contact with the latter being mainly responsible for the thermocouple-derived temperatures. It is estimated that for a catalyst working at 300 °C there is at least a 190 °C temperature difference between the silica and metal components.

Attempts to observe selective emissions from surface species under static or reaction conditions were unsuccessful. Apparent selective emissions were observed when the spectrum from the catalyst in contact with CO or CO/O₂ was ratioed for reference against that of the bare evacuated catalyst at the same temperature. These proved to be experiment artefacts associated with temperature gradients within the evacuated catalyst.