High‐Resolution 3D Proton MRI of Hyperpolarized Gas Enabled by Parahydrogen and Rh/TiO₂ Heterogeneous Catalyst

Abstract

Several supported metal catalysts were synthesized, characterized, and tested in heterogeneous hydrogenation of propene with parahydrogen to maximize nuclear spin hyperpolarization of propane gas using parahydrogen induced polarization (PHIP). The Rh/TiO2 catalyst with a metal particle size of 1.6 nm was found to be the most active and effective in the pairwise hydrogen addition and robust, demonstrating reproducible results with multiple hydrogenation experiments and stability for ≥1.5 years. 3D 1H magnetic resonance imaging (MRI) of 1 % hyperpolarized flowing gas with microscale spatial resolution (625 × 625 × 625 μm3) and large imaging matrix (128 × 128 × 32) was demonstrated by using a preclinical 4.7 T scanner and 17.4 s imaging scan time.

Strong Metal–Support Interactions for Palladium Supported on TiO2 Catalysts in the Heterogeneous Hydrogenation with Parahydrogen

“…[12,13] Remarkably,t itania-supported metal catalysts were shown to exhibit much higher levels of the pairwise addition of hydrogen (and larger PHIP effects) relative to that exhibited by metals on other supports. [9,14] Therefore, examination of the nature of the active sites for titania-supported nanoparticles in the contexto ft he pairwise addition of hydrogen may open up new possibilities for the rational preparation of catalysts that are able to maximize the observed PHIP effects and for the production of hyperpolarizedm olecular contrast agents potentially suitable for in vivo magnetic resonance imaging investigations. [14][15][16] In catalysis, it is well known that metals supported on titania exhibit the strong metal-support interaction (SMSI) effect.…”

“…[9,14] Therefore, examination of the nature of the active sites for titania-supported nanoparticles in the contexto ft he pairwise addition of hydrogen may open up new possibilities for the rational preparation of catalysts that are able to maximize the observed PHIP effects and for the production of hyperpolarizedm olecular contrast agents potentially suitable for in vivo magnetic resonance imaging investigations. [14][15][16] In catalysis, it is well known that metals supported on titania exhibit the strong metal-support interaction (SMSI) effect. [17,18] This phenomenoni sk nown to modifyt he selectivity and activity of ac atalyst.…”

Toward production of pure 13C hyperpolarized metabolites using heterogeneous parahydrogen-induced polarization of ethyl[1-13C]acetate

“…depolarize within seconds. 17 To increase short lifetime of HP fluids, more sophisticated agents with 13 C labeled sites were developed, where these 13 C sites are hyperpolarized via polarization transfer from nascent parahydrogen atoms using spin-spin couplings. While this polarization transfer can be accomplished by radio frequency pulse sequences, a less instrumentation demanding alternative is a magnetic field cycling (MFC) approach.…”

“…17 Therefore, two variants of Rh/TiO 2 catalysts corresponding to two different loadings of the metal (1 wt% and 23.2 wt%) were prepared (see ESI for details).…”

NMR Hyperpolarization Techniques of Gases

“…Note that the nature of the heterogeneous solid catalyst can have a significant impact on the polarization level, and titania-supported metal catalysts were shown to exhibit larger PHIP effects compared to metals on other supports. [215] The polarization level for HP gases produced over supported metal catalysts can be several percent, [28b, 216] and it increases with the decrease in the size of the supported metal nanoparticles. [217] …”