(461f) CO2 Hydrogenation on Silica- and Titania- Supported Single-Site Heterogeneous CoII Catalyst

Global climate change has been widely attributed to the rising amounts of CO₂ in the atmosphere^[1,2]. Furthermore, there exist little uses for pure carbon dioxide meaning it must be chemically upgraded into a more valuable chemical. However, one of the main difficulties with reducing CO₂ via chemical conversion is the thermodynamic stability of the compound^[3]. To mitigate this barrier, cobalt catalyst have been studied for the CO₂ hydrogenation reaction due to their high activity and stability^[4]. Literature has shown that single-site catalysts yield higher turnover frequencies than nanoparticles catalyst for both hydrogenation and oxidation reactions^[5,6]. Furthermore, a unique feature of single-site catalyst is the uniformity of the active sites, which allows for a direct correlation between catalytic activity and the structure of the sites. However, to the best of our knowledge, no work has been done on the use of single-site heterogeneous catalyst for CO₂ hydrogenation.

In this presentation, single-site Co^II catalyst for the CO₂ hydrogenation will be discussed. Single-site Co supported on silica are synthesized using methods adapted from literature^[5]. Since the active site for this reaction is the highly stable Co^II center, titania was also explored as a support due to its strong metal-support interaction with Co in the oxidized state^[4], leading to enhanced activity compared to silica supported Co catalyst. The stability of the Co^II active site comes from its tetrahedral geometry with neighboring oxygens from the oxide supports. Understanding the interactions with isolated metal ions with a uniform active site can provide insight into the mechanism of CO₂ hydrogenation, which is still widely debated. In order to obtain a detailed understanding of the catalytic activity of the single-site Co^II we must verify the surface species are in an isolated geometry. To this end the techniques that will be used to characterize the surface are Raman spectroscopy, diffuse reflectance UV-vis, TPR, and STEM-HAADF. These characterization techniques coupled with reaction data can correlate the activity of single-site heterogeneous Co^II catalyst for CO₂ hydrogenation.

References

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[2] M. Meinshausen, N. Meinshausen, W. Hare, S. C. B. Raper, K. Frieler, R. Knutti, D. J. Frame, M. R. Allen, Nature 2009, 458, 1158â??62.

[3] H. Arakawa, M. Aresta, J. N. Armor, M. A. Barteau, E. J. Beckman, A. T. Bell, J. E. Bercaw, C. Creutz, E. Dinjus, D. A. Dixon, et al., Chem. Rev. 2001, 101, 953â??996.

[4] G. Melaet, W. T. Ralston, C.-S. Li, S. Alayoglu, K. An, N. Musselwhite, B. Kalkan, G. a. Somorjai, J. Am. Chem. Soc. 2014, 136, 2260â??2263.

[5] B. Hu, A. â??Beanâ? Getsoian, N. M. Schweitzer, U. Das, H. Kim, J. Niklas, O. Poluektov, L. A. Curtiss, P. C. Stair, J. T. Miller, et al., J. Catal. 2015, 322, 24â??37.

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