Silicalite-1 Layer Secures the Bifunctional Nature of a CO 2 Hydrogenation Catalyst.

Close proximity usually shortens the travel distance of reaction intermediates, thus able to promote the catalytic performance of CO 2 hydrogenation by a bifunctional catalyst, such as the widely reported In 2 O 3 /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 In 2 O 3 surface, thus resulting in catalyst deactivation. Additionally, zeolite coking is another potential deactivation factor when dealing with this methanol-mediated CO 2 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 In 2 O 3 /H-ZSM-5-catalyzed CO 2 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 In 2 O 3 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 C 2 + 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 CO 2 hydrogenation catalyst.