(511c) Characterizing Heterogeneous Aging of a Monolith-Supported Oxidation Catalyst

A Pt/Al2O3 monolith-supported catalyst was investigated with propylene oxidation before and after thermal aging and SO2 exposure. Spatially-resolved capillary inlet mass spectrometry (SpaciMS) and infra-red thermography techniques were used to monitor reaction location, and how this changes with aging. Heterogeneous thermal aging produced higher temperature exposures at the catalyst inlet than at downstream locations, focusing the damage at the upstream portion of the catalyst.

Following each thermal aging cycle, the temperature for propylene oxidation light-off increased. The position of the peak temperature rises within the catalyst during back-to-front ignition also shifted location. Over the fresh catalyst, the highest temperature peak value was located at the catalyst inlet, while after aging the temperature peaks in the middle portion of the catalyst grew and at the inlet portion decreased. As well, the temperature and concentration wave traveling speeds decreased with aging. In a previous homogeneous aging study, the peak wave speed also decreased following aging, but the effect was seen throughout the catalyst [1], while following heterogeneous aging the speed decrease was more drastic and focussed in the front of the catalyst. During steady state oxidation tests, the reaction zone moved downstream in the catalyst for each aging cycle, and increased in width. These effects were all more apparent for at a lower propylene concentration. The response to step concentration changes was very dependent on the preceding reaction state, with three different responses to step increases seen. When light-off at the back of the catalyst was followed by back-to-front ignition such that the reaction zone was at the inlet, increasing the concentration shifted the reaction zone downstream. When light-off had occurred but back-to-front ignition had not, increasing the concentration move the reaction zone upstream. When light-off had not occurred, increasing the concentration caused reaction extinction. Effects of S exposure on the same temperature and concentration/reaction zone trends will also be presented.

REFERENCE 1. Shakir, O; Yezerets, A.; Currier, N.; and Epling, W.S., Appl. Catal. A: Gen. 365, 301(2009).