Investigating the coupling between transport and reaction within a catalyst pellet using operando magnetic resonance spectroscopic imaging

Abstract

In heterogeneous catalysis, the distribution of reactant and product species within a catalyst pellet are of central importance to the catalyst performance, and ultimately to the overall conversion and selectivity achieved in commercial-scale reactors. Despite this importance, fundamental understanding of pellet scale behaviour at operando conditions is limited due to the coupled, multi-scale nature of the underlying transport processes, and the limited techniques capable of mapping the intra-pellet composition at industrially relevant length scales. Here, we demonstrate the coupling between transport and reaction at the pellet scale by using operando magnetic resonance spectroscopic imaging (MRSI) to map the liquid composition within Pd/γ-Al2O3 catalyst pellets at an isotropic in-plane spatial resolution of 86 µm during a styrene hydrogenation reaction. The results reveal that asymmetric liquid wetting at the pellet surface, typical of that occurring in trickle-bed reactors, causes significant composition heterogeneity across a catalyst pellet. Due to the wetting inhomogeneity, commonly used 1D reaction-diffusion models are inadequate for describing the observed composition heterogeneity across the pellet. The results reported here provide unique experimental insight into the coupling between transport and reaction at the pellet scale within an operating reactor.