Fabrication of a PdCu@SiO2@Cu core–shell–satellite catalyst for the selective hydrogenation of acetylene

Abstract

Pd₂₅Cu₇₅@SiO₂ core–shell and PdCu@SiO₂@Cu core–shell–satellite architectures were fabricated by silica-coating of Pd₂₅Cu₇₅ colloids in a reverse microemulsion. Hydrolysis of tetraethylorthosilicate in the reverse microemulsion containing hydrazine and ammonia yielded a core–shell structure, while the use of ammonia only, instead of a mixture of hydrazine and ammonia, formed a core–shell–satellite structure. The ammonia-leached copper species migrated onto the developing silica shell and formed smaller Cu clusters. Air-calcination at 673 K followed by H₂-reduction at 773 K of the as-synthesized samples removed the organic surfactants and generated the permeable porous silica shells. The core–shell catalyst consisted of a metal core (8.5 nm) and a silica shell (7.8 nm), while the core–shell–satellite catalyst was composed by a metal core (7.0 nm), a silica shell (8.0 nm), and satellite Cu clusters (1.4 nm) on the silica shell. When used to catalyze the selective hydrogenation of acetylene to ethylene, the core–shell–satellite catalyst showed substantially enhanced activity and stability because of the synergetic catalysis between the metal core and the surrounding Cu clusters.