COKE PROFILES IN DEACTIVATED ALUMINA PELLETS STUDIED BY NMR IMAGING

Deactivation of industrial catalysts by coke is of great industrial importance. The subject continues to attract much attention because all organic reactions on solid catalysts are accompanied by the formation of coke. This paper presents a new technique to visualise the coke profile within a deactivated alumina pellet. The nuclear magnetic resonance (NMR) images presented in this paper have been obtained using the gradient-reversal technique, and represent the first application of NMR imaging to the study of catalyst deactivation. The NMR images reveal additional information describing the coke profile within the alumina pellet to that which can be obtained using conventional methods. In particular, the images show that deposition of coke within the pellet is inconsistent with the shrinking-core model supported by visual observation. Instead, coke deposition within the interior of the pellet is heterogeneous and, we suggest, directly related to structural heterogeneities associated with the pellet itself.