Mesoporous Silica Encapsulated Platinum-Tin IntermetallicNanoparticles Catalyze Hydrogenation with an Unprecedented 20%Pairwise Selectivity for Parahydrogen Enhanced Nuclear MagneticResonance

Supported noble metals offer key advantages over homogeneous catalysts for invivo applications of parahydrogen-based hyperpolarization. However, their performance iscompromised by randomization of parahydrogen spin order resulting from rapid hydrogenadatom diffusion. The diffusion on Pt surfaces can be suppressed by introduction of Sn to formPt-Sn intermetallic phases. Herein, an unprecedented pairwise selectivity of 19.7 +/- 1.1% in theheterogeneous hydrogenation of propyne using silica encapsulated Pt-Sn intermetallicnanoparticles is reported. This high level of selectivity exceeds that of all supported metalcatalysts by at least a factor of 3. Moreover, the pairwise selectivity for alkyne hydrogenation isabout 2 times higher than for alkene hydrogenation, an observation attributed to the highercoverage of the former and its effect on diffusion. Lastly, PtSn@mSiO2nanoparticles exhibitedimproved coking resistance, and any loss of activity is shown to be fully reversible throughhigh-temperature oxidation-reduction cycling