Silicalite-1 Layer Secures the Bifunctional Nature of a CO2 Hydrogenation Catalyst

Abstract

Close proximity usually shortens the travel distance of reaction intermediates, thus able to promote the catalytic performance of CO2 hydrogenation by a bifunctional catalyst, such as the widely reported In2O3/H-ZSM-5. However, nanoscale proximity (e.g., powder mixing, PM) more likely causes the fast deactivation of the catalyst, probably due to the migration of metals (e.g., In) that not only neutralizes the acid sites of zeolites but also leads to the reconstruction of the In2O3 surface, thus resulting in catalyst deactivation. Additionally, zeolite coking is another potential deactivation factor when dealing with this methanol-mediated CO2 hydrogenation process. Herein, we reported a facile approach to overcome these three challenges by coating a layer of silicalite-1 (S-1) shell outside a zeolite H-ZSM-5 crystal for the In2O3/H-ZSM-5-catalyzed CO2 hydrogenation. More specifically, the S-1 layer (1) restrains the migration of indium that preserved the acidity of H-ZSM-5 and at the same time (2) prevents the over-reduction of the In2O3 phase and (3) improves the catalyst lifetime by suppressing the aromatic cycle in a methanol-to-hydrocarbon conversion step. As such, the activity for the synthesis of C2+ hydrocarbons under nanoscale proximity (PM) was successfully obtained. Moreover, an enhanced performance was observed for the S-1-coated catalyst under microscale proximity (e.g., granule mixing, GM) in comparison to the S-1-coating-free counterpart. This work highlights an effective shielding strategy to secure the bifunctional nature of a CO2 hydrogenation catalyst.