City Research Online

Abstract

This investigation involves a study of the processes that cause deactivation of supported precious metal catalysts during the oxidation of methane. Of particular interest were the causes of loss in activity observed for catalytic beads which are used for the detection and estimation of hydrocarbons. Initially, the kinetics and mechanism of methane oxidation were studied using a pulse-flow microreactor in the presence and in the absence of gaseous oxygen. The orders of reaction and activation energies are in good agreement with those obtained by other investigators. A Langmuir- Hinshelwood mechanism with reaction between adsorbed methane and adsorbed oxygen is proposed.

The effects of thermal deactivation and self-poisoning on the oxidation of methane were shown to be severe only under extreme conditions. Although water vapour had no lasting effect on powder catalysts in the microreactor, it could cause loss of activity for catalytic beads in a static reactor. Deactivation by carbon deposition was unlikely to affect the catalyst as long as contact times remained short and oxygen was present in excess. Both the support and the precious metal underwent some physical changes at higher temperatures but, although severe agglomeration of catalyst particles occurred, methane oxidation remained substantially unaffected.

Addition of small amounts of inhibitors such as halocarbons and organosiloxanes to the reactants caused some loss in activity for hydrocarbon oxidation. The support played a significant role in the degree of deactivation observed for the precious metal and the ability of the catalyst to recover from inhibition depended to some extent on the support used. Supports for which strong precious metal-support interactions were present tended to affect beneficially the ability of the catalyst to recover. Surface analysis techniques such as transmission electron microscopy, Auger electron spectroscopy and X-ray photoelectron spectroscopy were applied to provide information as to the effect of the inhibitor on the precious metal and support as well as the fate of the inhibitor, both during and after inhibition. The possible mechanisms by which inhibition occurred are discussed.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > Q Science (General) Q Science > QD Chemistry T Technology > TP Chemical technology
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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