(84u) CO2 Upgradation By Methane Coupling on Metal Ion-Exchanged Zeolites

The coupling of CO₂ and methane to form acetic acid and other oxygenates provides an atom-efficient way to convert two greenhouse gases to a valuable chemical. Such a transformation consumes less energy compared to CO2 utilization via catalytic reduction [1]. However, one of the key challenges is that the reported yield of acetic acid through this reaction is very low. Therefore it is necessary to identify a suitable catalyst for this transformation. Wu et al. [2] have determined that Zn²⁺ in Zn-ZSM-5 can heterolytically activate methane into [Zn-CH3]⁺ even at relatively mild temperatures. As a result, Zn-substituted zeolites have received much research attention in recent years [3].

While these catalysts have already been studied in batch conditions [3], optimizing under flow reactor conditions facilitates mechanistic studies and scale-up. In this work, various Zn-exchanged zeolites are considered and the effects of zeolitic support framework type (MFI, MOR) and acidity (different Si/Al), and metal loading of substituted metal (Zn) are studied at optimized reaction condition in a flow reactor. Computational studies by Zhang et al. [4] have identified that monovalent Zn²⁺ species located in the channel sites (straight and sinusoidal) of MFI zeolite exhibit the best catalytic activity [4]. While significant efforts have been put into post-synthetic modifications of ZSM-5, we have also synthesized ZSM-5 with selective Al-sites (to tune Al site population in either of the channels) suitable for effective Zn substitution in this study and their activity for CO₂ conversion will be analysed.

References

1. Álvarez ,A., et al., ChemPhysChem, 18 (2017) 3135–41.
2. Wu, J.-F., et al., J. Am. Chem. Soc., 135 (2013) 13567–73.
3. Shavi, R., et al., Appl. Catal. B: Environ., 229 (2018) 237–48.
4. Zhang, P., et al., Catal. Sci. Technol., 9 (2019) 6297–307.