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.

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Parahydrogen-induced polarization (PHIP) was successfully utilized to demonstrate the strong metal-support interaction (SMSI) effect for palladium supported on titania catalysts. Heterogeneous hydrogenation of 1,3-butadiene over Pd/TiO 2 catalysts led to the formation of 1-and 2-butenes and butane, and hyperpolarized products were obtained if parahydrogen was used in the reaction. However,i fthe catalysts were reduced in H 2 flow at 500 8Cb efore the hydrogenation reaction, the observed polarization levels were significantly lower or even zero, which was indicative of the suppression of the pairwise addition of hydrogen route. This observation indicated the possibility to detect the SMSI effect by the PHIP technique. Moreover, by using X-ray photoelectron spectroscopy it wass hown that Pd is partially presentasPd d + after reduction under ahydrogen atmosphere at 500 8C. These results were confirmed by transmissione lectron microscopy,w hich revealed the formation of Pd d + and the dissolution of Pd in the titania lattice.The hydrogenation of unsaturated compounds with parahydrogen leads to the observation of the parahydrogen-induced polarization (PHIP) phenomenon. [1,2] This resultsi nas ignificant enhancement in the NMR signals of the corresponding reaction products or intermediates. In the case of homogeneous catalytic hydrogenation, as ingle metal center often plays the role of the active site for hydrogen activation, and therefore, the pairwise hydrogen addition route is the major mechanism for such processes. [3,4] In contrast, heterogeneous pairwise addition of hydrogen is uncommon. Nevertheless, it can be successfully observed by the PHIP technique, [5][6][7] contrary to the implications of the Horiuti-Polanyi mechanism [8] widely accepted for ab road range of supported metal nanoparticles. Therefore, understanding the nature of active sites that can add two hydrogen atoms from the same hydrogen molecule as ap air to asubstrate molecule is ah ighly important task. [9][10][11] Recently,i tw as shown that the nature of the catalyst support can have as ignificant impact on the rate of the pairwise addition of hydrogen. [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. [17,18] This phenomenoni sk nown to modifyt he selectivity and activity of ac atalyst. [19,20] Therefore, significant alteration in the s...

Heterogeneous hydrogenation of α,β-unsaturated carbonyl compounds was addressed using the parahydrogen-induced polarization (PHIP) technique. PHIP effects were observed in hydrogenation of CC bond of acrolein and crotonaldehyde over different supported metal catalysts, demonstrating the existence of a pairwise route of hydrogen addition to the substrate. Hydrogenation of acrolein over Pd–Sn/Al2O3, Pd–Sn/TiO2, Pd–Zn/TiO2, and Pd/TiO2 catalysts with parahydrogen also led to the polarization of the proton of CHO group of propanal. This was explained by C­(O)–H bond dissociation which represents a side process on the catalyst surface. Formation of polarized cis- and trans-2-butenes was detected in hydrogenation of acrolein with parahydrogen over several Rh-based catalysts. This observation is made possible only due to the high NMR signal enhancement provided by PHIP. It was also found that hydrogenation of acetone and propanal with parahydrogen leads to polarized propane formation as a result of C–O bond hydrogenolysis.