Invited Speaker 23rd International Society of Magnetic Resonance Conference 2023

Parahydrogen-induced polarization and heterogeneous catalysis (#184)

Igor V. Koptyug 1
  1. International Tomography Center, SB RAS, Novosibirsk, Russia

Originally proposed and demonstrated with homogeneous catalysis [1,2], parahydrogen-induced polarization (PHIP) has by now become one of the most powerful nuclear spin hyperpolarization techniques [3]. Its extension to heterogeneous hydrogenations (HET-PHIP) was introduced about 15 years ago [4,5]. While currently the latter usually suffers from lower polarization levels compared to its homogeneous counterpart, several potential advantages make further efforts to advance this approach worthwhile: i) it can be used to produce contaminant-free hyperpolarized liquids and gases without additional purification stages and associated polarization losses; ii) it can become a powerful tool for the mechanistic and operando MRI/MRS studies of industrial catalytic processes aided by a major sensitivity boost; iii) it can provide a practical solution for the enrichment of nuclear spin isomers of symmetric molecules other than H2, which would be highly beneficial for studying their fundamental properties, developing novel hyperpolarization schemes, exploring a much broader range of chemical reactions, and a lot more.

Further progress with these endeavors requires heterogeneous catalysts capable of achieving a higher degree of parahydrogen spin order transfer to reaction intermediates and products. And while a reasonable improvement in HET-PHIP efficiency was achieved to date by exploring different catalyst types, any rational catalyst design requires a detailed understanding of the physical and chemical mechanisms involved. Currently, some key questions remain unanswered, and in particular, observation of HET-PHIP effects with supported and unsupported metal (nano)particles is far from being fully understood.

In this presentation, a rationale for the PHIP effects in heterogeneous catalysis will be advanced, which is supported by relevant model calculations and is in a general agreement with the experimental observations reported in HET-PHIP studies. These results suggest that a paradigm shift is likely required in the current theory and practice of this research field.

Acknowledgment. This work was financially supported by RSF (grant # 22-43-04426).

  1. C.R. Bowers, D.P. Weitekamp, Phys. Rev. Lett., 57, 2645 (1986).
  2. C.R. Bowers, D.P. Weitekamp, J. Am. Chem. Soc., 109, 5541 (1987).
  3. J. Eills, D. Budker, S. Cavagnero, E.Y. Chekmenev, S.J. Elliott, S. Jannin, A. Lesage, J. Matysik, T. Meersmann, T. Prisner, J.A. Reimer, H. Yang, I.V. Koptyug, Chem. Rev., 123, 1417 (2023).
  4. I.V. Koptyug, K.V. Kovtunov, S.R. Burt, M.S. Anwar, C. Hilty, S. Han, A. Pines, R.Z. Sagdeev, J. Am. Chem. Soc., 129, 5580 (2007).
  5. K.V. Kovtunov, I.E. Beck, V.I. Bukhtiyarov, I.V. Koptyug, Angew. Chem. Int. Ed., 47, 1492 (2008).