(656a) Tuning CO2 Hydrogenation at Polymer/Metal Interfaces

Specification and optimization of the active centers of a catalyst have long been a challenge in catalysis. Thus far, numerous efforts have been spent on trying to modify the active sites in heterogeneous catalysts^1-3. Complementarily, the conversion of CO₂ into value-added chemicals such as lower olefins and liquid fuels is attractive due to its potential in mitigating CO₂ emissions. However, limitations on rates and selectivity arise due to limited control on individual active site motifs. In this work, we demonstrate that we can tune active site selectivity at the polymer/metal interface, where Ru/TiO₂ is conformally encapsulated into functional imine-based porous organic framework (IPOF) layers. As shown in Figure 1, IPOF overlayers were conformally deposited onto Ru/TiO₂ catalysts by carefully controlling the synthesis conditions. It is worth mentioning that unlike commonly reported imine-based covalent organic framework synthesis, which require a dynamic crystallization time of a few days, the overcoating procedure only took 1 hour to finish. The aforementioned catalysts were then tested for CO₂ hydrogenation under 6 bar at 250 °C, since control tests demonstrate the stability of these materials under the studied reaction conditions. As for bare Ru/TiO₂ sample, methane was the major product, and only minor amounts of ethane and propane were formed, in agreement with literature.⁴ Interestingly, the encapsulated sample showed different product distribution, with much enhanced >C₂ hydrocarbon production rate and selectivity. Specifically, encapsulation resulted in ~2 and ~5 fold enhancement in ethane and propane production, respectively. Notably, butane production was detectable only with encapsulated sample. Fundamental studies on this material inspires rational design of active sites for selective transformations.

References

1. Ren et al, Chem. Int. Ed. 58, 14483 –14488 (2019)
2. Zhang et al, Catal. 1, 148-155 (2018)
3. Riscoe et al, Catal. 2, 852-863 (2019)
4. Xu et al, Catal. 333, 227-237 (2016)