Alkyne hydrogenation using Pd–Ag hybrid nanocatalysts in surface‐immobilized dendrimers

Abstract

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.

Advances in the preparation of highly selective nanocatalysts for the semi-hydrogenation of alkynes using colloidal approaches

“…The preparation of a series of core-shell PdAg NPs (Pd : Ag ratios of 40 : 60, 50 : 50, and 60 : 40) was achieved by coreduction of Pd-Ag salts (using NaBH 4 as the reducing agent) in the presence of poly( propylene imine) dendrimers covalently bound to the surface of a silica polyamine composite. 111 In this approach, the poly( propylene imine) dendrimers play the role of stabilizers of the NPs. Based on XPS analysis, the authors proposed a core-shell structure of the PdAg NPs where silver dominates the outer shell.…”

“…124 They concluded that Pd (211) is the most active site while Pd (111) is the most selective site for partial hydrogenation. For Pd (111) decorated with Cu, Ag and Au, the selectivity for the hydrogenation of acetylene to ethylene is enhanced. Adsorption energies of ethylene and activation barriers justify these results.…”

Dendrimer‐Encapsulated Pd Nanoparticles, Immobilized in Silica Pores, as Catalysts for Selective Hydrogenation of Unsaturated Compounds

“…Herein anchoring the dendrimers was performed, considering the space, occupied by the latters on surface of the carrier. Impregnated with Pd and PdAg nanoparticles, this material was characterized by regular and narrow particle size distribution and proved its high efficacy and stability in selective hydrogenation of phenyl acetylene, linear alkynes and conjugated dienes . Similar approach was earlier applied for ready poly(ether imine) phosphine modified dendrimer, anchored to amorphous silica, preliminary functionalized with 3‐chloropropylsilane .…”

Preparation of Poly(ethylene glycol)@Polyurea Microcapsules Using Oil/Oil Emulsions and Their Application as Microreactors

“…However, despite their great reactivity and selectivity, metal nanoparticles require additional immobilization techniques to avoid their aggregation, and usually involve the use of different supports to enable catalyst recovery. The uses of organic polymer supports [ 14 , 15 , 16 ], dendrimers [ 17 , 18 , 19 ], supported ionic liquid phase (SILP) catalysts [ 20 , 21 , 22 ], magnetic nanoparticles (MNPs) [ 23 , 24 , 25 ], and inorganic supports [ 26 , 27 , 28 ] are just a few examples of many immobilization techniques available for metal nanoparticles. However, along with leaching problems, these methods generally involve multiple synthetic steps and pre-functionalization processes, which make the development of new catalysts difficult, expensive, and cumbersome.…”