Palladium nanoparticles on dendrimer-containing supports as catalysts for hydrogenation of unsaturated hydrocarbons

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

“…Also G3‐dendr‐SiO 2 ‐Pd sample contained a low, but noticeable portion of Pd 2+ ions, strongly bounded with the dendrimer fragments (Table ). Analogous tendency was earlier observed for Pd nanoparticles, encapsulated in PPI dendrimers of 3 rd generation, immobilized on the silica‐polyamine composite surface, as well as for Pd nanoparticles, encapsulated in high densely cross‐linked networks of PPI and PAMAM dendrimers …”

“…As a consequence, the same Pd nanoparticle can simultaneously adsorb linear alkyne molecules in rather large quantity, as compared with those of phenylacetylene. On the other hand, alkyl substituents in the 1‐octyne, 4‐octyne and 1‐hexyne molecules possess the weak + I ‐effect, that facilitates substrate adsorption on Pd nanoparticles – in contrast to weak − M ‐effect of phenyl ring in the phenylacetylene molecule ,…”

“…The presence of basic dendrimer amino groups strengthens polarization of terminal C−H bond near to the C≡C triple bond in phenylacetylene molecule and, as a consequence, the acidity of the terminal proton. On the one hand, it leads to increase in the electron density on the C≡C triple bond and, as a consequence, to the enhanced selectivity on styrene . On the other hand, it favours to the predominant perpendicular adsorption of phenylacetylene molecule, not suitable for the subsequent hydrogenation to styrene.…”

“…It results in Pd nanoparticles, stabilized by the large amount of donor amino groups simultaneously ,,. As a consequence, Pd surface is partly filled with electrons and much stronger adsorbs phenylacetylene with its high electron density on the C≡C triple bond (additionally polarized by the interactions with the basic dendrimer amino groups) in comparison with styrene, resulting both in higher reaction rate and selectivity on styrene ,,. Herein for organo‐silica dendrimer‐based catalysts a positive dendritic effect was observed: the more dendrimer's generation, the more donor amino groups it has and, as a consequence, the more stabilized and electron‐enriched nanoparticles appearing to be.…”

“…It was demonstrated, that the nature and generation of dendrimer used, the nature, size and rigidity of cross‐linking agent, as well as the synthesis conditions (temperature, solvent and the presence of polymeric template) had an essential influence on both physical chemical properties (particles size distribution, metal weight content, metal surface valency states etc. ), activity and selectivity of the catalyst obtained ,…”