Cyclopropane Hydrogenation vs Isomerization over Pt and Pt–Sn Intermetallic Nanoparticle Catalysts: A Parahydrogen Spin-Labeling Study

Hyperpolarized propane produced by heterogeneous hydrogenation of cyclopropane with parahydrogen has been proposed as a safe inhalant for sensitivity-enhanced in vivo magnetic resonance imaging. The present studies were initially motivated by the possibility to improve the pairwise selectivity of hydrogenation using Pt–Sn intermetallic nanoparticle catalysts which achieved a record high pairwise selectivity in the hydrogenation of propene. The performance of the Pt₃Sn catalysts is found to be comparable to that of the Rh/TiO₂ catalyst employed in a recent publication. However, significant amounts of propene are also produced by isomerization over the Pt–Sn catalysts. The isomerization is promoted by weakening of the propene–surface binding energy and depletion of the H adatom density. While this is a remarkable finding from the perspective of catalysis science, the isomerization to propene over the Pt–Sn catalysts negates the advantages of using cyclopropane rather than propene as the safer reactant for in vivo use.