Alkyne hydrogenation using Pd-Ag hybrid nanocatalysts in surface-immobilized dendrimers

A series of Pd-Ag mixed-metal nanocatalysts were prepared by reduction of Pd-Ag salts in the presence of poly(propylene imine) dendrimers, which were covalently bound to the surface of a silica polyamine composite, BP-1 (polyallylamine covalently bound to a silanized amorphous silica gel). Three different Pd-to-Ag ratios were evaluated (50:50, catalyst 1; 40:60, catalyst 2; 60:40, catalyst 3) with the goal of determining how the amount of Ag effects selectivity, rate and conversion in the selective reduction of alkynes, such as phenylacetylene and 1- or 4-octyne, to the corresponding alkenes. Conditions for the catalysis are reported where there is improved selectivity without a serious reduction in rate when compared with the analogous Pd-only catalysts. Catalyst 2 worked best for phenylacetylene and catalyst 3 worked best for the octynes. The catalysts could be reused seven times without loss of activity. Copyright (c) 2015 John Wiley & Sons, Ltd.