Palladium with interstitial carbon atoms as a catalyst for ultraselective hydrogenation in the liquid phase

We report a green route to prepare Pd with interstitial carbon atoms as a new solid catalyst for fine chemical catalysis in the liquid phase. First, glucose was used as a reducing and capping agent under hydrothermal conditions for the controlled reduction of the Pd precursor and after thermal treatment, carbon atoms were found to occupy the Pd subsurface interstitial sites, as confirmed by PXRD and TPR. A simple hydrogen peroxide treatment was required to partially remove surface carbon to increase catalytic activity. Catalytic properties of the final material were investigated in the hydrogenation of 3-hexyn-1-ol and 4-octyne to the corresponding alkene products and compared with a classical Lindlar type catalyst and other commercial Pd/C. It was found that the carbonised glucose Pd nanocatalyst with subsurface carbon substantially reduced undesirable isomerisations and over-hydrogenations. This was achieved by the increase in desorption rates of alkene species in solution, an effect believed to be the result of hybridisation of the Pd d-state with the C sp-state, thereby increasing the overall cis-alkene selectivity.