Selective Single-Site Pd-In Hydrogenation Catalyst for Production of Enhanced Magnetic Resonance Signals using Parahydrogen

Pd-In/Al2O3 single-site catalyst was able to show high selectivity (up to 98%) in the gas phase semi-hydrogenation of propyne. Formation of intermetallic Pd-In compound was studied by XPS during reduction of the catalyst. FTIR-CO spectroscopy confirmed single-site nature of the intermetallic Pd-In phase reduced at high temperature. Utilization of Pd-In/Al2O3 in semi-hydrogenation of propyne with parahydrogen allowed to produce approximate to 3400-fold NMR signal enhancement for reaction product propene (polarization = 9.3 %), demonstrating the large contribution of pairwise hydrogen addition route. Significant signal enhancement as well as the high catalytic activity of the Pd-In catalyst allowed to acquire H-1 MR images of flowing hyperpolarized propene gas selectively for protons in CH, CH2 and CH3 groups. This observation is unique and can be easily transferred to the development of a useful MRI technique for an in situ investigation of selective semihydrogenation in catalytic reactors.