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: Pd-1/ND@G with a monoatomic Pd distribution (0.11 wt %) and Pd-n/ND@G comprising supported metal clusters (0.87 wt %). The monoatomic distribution of Pd in Pd-1/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 H-2 addition to propyne was compared under the same experimental conditions by observing H-1 NMR signal enhancements provided by the parahydrogen-induced polarization (PHIP) effect. The enhancements produced by the Pd-1/ND@G catalyst were found to be ca. 6-fold larger than those observed with Pd-n/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.