In the last decade, the semi-hydrogenation of alkynes has experienced significant advances in terms of fine control of alkene selectivity and prevention of the over-hydrogenation reaction. Such advances have been possible to a large extent through the progress in colloidal methods for the preparation of metallic nanoparticles. The present review describes the contributions in the field of the selective hydrogenation of alkynes involving the utilization of colloidal methodologies. These approaches permit the fine modulation of several parameters affecting the catalytic performance of the active phase such as the particle size, the bulk and the surface structure and composition. For the transformation of liquid substrates, the nature of the stabilizers, the reducing agents and the metal precursors employed for the synthesis of the catalysts can be tuned to enhance the alkene selectivity. In contrast, in catalytic transformations of gaseous substrates, the presence of adsorbed species at the metal surface usually gives detrimental results while the interplay between the support and the active phase appears to be a more convincing alternative for catalyst tuning.

In the present paper, we report the synthesis of highly functionalized nanomaterials carefully nanoengineered to catalyze the semi‐hydrogenation of acetylene in ethylene‐rich mixtures. Surface functionalization and structure modification of a series of bimetallic PdAg nanoparticles was performed using HHDMA as stabilizer and alloying the active palladium phase with silver. Bimetallic PdAg NPs with adjustable Pd/Ag ratio were prepared in water through a novel one‐pot methodology using hydrogen gas as a benign reducing agent and cyanide as additive. UV‐Vis studies indicated the formation of the bimetallic nanostructures through a sequential displacement‐galvanic reduction process mediated by cyanide. The series of colloidal NPs were deposited onto alumina and successfully applied as catalysts in the selective hydrogenation of acetylene in ethylene rich mixtures. Geometric and electronic promotion of Ag over Pd based catalysts was evidenced by the increase of the ethylene selectivity with the Ag content. The reactivity of these materials demonstrated the applicability of HHDMA stabilized NPs in a gas phase reaction of industrial interest and the success of combining several strategies for the enhancement of the alkene selectivity.