(36g) Catalytic Performance of Iron Encapsulated in ZSM-5 for CO2 and CO Hydrogenation

Catalytic conversion of CO₂ into chemicals and fuels, such as lower olefins, is one of the most viable ways of reducing atmospheric CO₂ to alleviate the negative effects of climate change. One option for reducing CO₂ to chemicals and fuels is through reverse water-gas shift (RWGS) combined with Fischer-Tropsch Synthesis (FTS) [1]. Supported metal catalysts have been widely researched for CO₂ hydrogenation, but they have limited applicability due to low activity, selectivity, and deactivation caused by coke deposition and sintering of metal particles [2].

In this work, ZSM-5 zeolites are used to encapsulate Fe (Fe@ZSM-5) via a seed-directed growth technique. Fe@ZSM-5 improves the catalytic performance by suppressing metal nanoparticle agglomeration, preserving the number of active sites and tuning the selectivity toward light olefins via secondary reactions between the primary products and ZSM-5.

Initial XRD characterization results indicate the crystalline structure of both the Fe oxide and ZSM-5 is preserved within the Fe@ZSM-5. TEM images of Fe@ZSM-5 contain clear voids that likely result in increased CO₂ and CO uptake, with TPD profiles that are broadened and shifted toward higher temperatures when compared with Fe/ZSM-5 control catalysts prepared via wet impregnation. Together, the characterization data suggest possible trapping of CO₂ and CO within the Fe@ZSM-5 and successful encapsulation of Fe. Packed bed reactor studies for RWGS and FTS show that Fe@ZSM-5 catalysts are active for both CO₂ and CO hydrogenation, with increased selectivity toward C₂-C₄ olefins versus the Fe/ZSM-5 control. However, Fe@ZSM-5 exhibits rapid deactivation, which can possibly be improved with a mesoporous ZSM-5 shell. The results of this study demonstrate that the seed-directed growth technique is a viable strategy to control catalytic selectivity during CO₂ and CO hydrogenation reactions.

1. Marc D. Porosoff, et al. Energy & Environmental Science9.1 (2016): 62-73.

2. Xie, Jingxiu, et al. ACS catal. 6.6 (2016): 4017-4024.