Pd on Nanodiamond/Graphene in Hydrogenation of Propyne with Parahydrogen

The catalytic behavior of Pd catalysts supported on a defective nanodiamond/graphene material (ND@G) was studied in propyne hydrogenation with parahydrogen, taking advantage of the possibility to control the character of metal distribution by changing metal loading. Two different catalysts were studied in this work: Pd1/ND@G with a monoatomic Pd distribution (0.11 wt %) and Pdn/ND@G comprising supported metal clusters (0.87 wt %). The monoatomic distribution of Pd in Pd1/ND@G was confirmed by XPS and HAADF-STEM methods. This catalyst demonstrated an outstanding selectivity to propene (up to 100%) in propyne hydrogenation. The activity of the two Pd catalysts in pairwise H2 addition to propyne was compared under the same experimental conditions by observing 1H NMR signal enhancements provided by the parahydrogen-induced polarization (PHIP) effect. The enhancements produced by the Pd1/ND@G catalyst were found to be ca. 6-fold larger than those observed with Pdn/ND@G, indicating that the character of metal distribution has important consequences for the performance of a catalyst and its efficiency in terms of PHIP effects.