Silicalite-1 Coating Secures the Bifunctional Nature of a CO2 Hydrogenation Catalyst: One Stone Three Birds
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.
Dr. XING Shiyou
Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences
Guangzhou 510640, China