Recently, Dr. XING Shiyou, the assistant professor of the Guangzhou Institute of Energy Conversion (GIEC), Chinese Academy of Sciences, cooperated with Prof. Bert Weckhuysen from Utrecht University in the Netherlands, has made an important progress on the manipulation of the bifunctional catalytic materials for CO₂ hydrogenation. Relevant results, entitled “Silicalite-1 Layer Secures the Bifunctional Nature of a CO₂ Hydrogenation Catalyst”, was published in JACS Au, the flagship journal of the American Chemical Society, and was selected as the cover article. Publication info: https://pubs.acs.org/doi/full/10.1021/jacsau.2c00621

Valorizing CO₂ with renewable H₂ by heterogeneous thermos-catalysis is a promising route to abate the issue of global warming and also offers a set of innovative fossil-free approaches for the synthesis of chemicals and fuels. A tandem catalytic process enabled by a bifunctional catalyst of In₂O₃ and zeolite, showing impressive performance in making hydrocarbons from CO₂, has attracted massive attentions. Within this approach, the metal oxide of In₂O₃ catalyzes CO₂ to methanol (CTM), which subsequently transforms into hydrocarbons over an acid functionality dispersed within a zeolite material through the so-called methanol-to-hydrocarbon (MTH) process.

It is believed that, for this type of tandem catalyst, a close distance can markedly boost the overall efficiency for carbon–carbon coupling, i.e., C₂⁺ synthesis, due to the facilitated transfer of the reaction intermediates. However, this catalyst usually suffers from a whole loss of catalytic activity, when the two active components were placed in a nanoscale proximity prepared by, for instance, powder mixing (PM). This is 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. In addition to that, zeolite coking is another potential deactivation factor when dealing with this methanol-mediated CO₂ hydrogenation process.

In this work, a facile approach was reported 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) restrained the migration of indium that preserved the acidity of H-ZSM-5 and at the same time (2) prevented the over-reduction of the In₂O₃ phase and (3) improved 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 retrieved. 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.

Contact:

Dr. XING Shiyou

Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences

(http://english.giec.cas.cn/)

Guangzhou 510640, China

E-mail: xingsy@ms.giec.ac.cn