Synthesis of monodispersed palladium nanoparticles to study structure sensitivity of solvent-free selective hydrogenation of 2-methyl-3-butyn-2-ol

Abstract

A novel method for isolation of monodispersed Pd nanoparticles from a reverse microemulsion was developed using hydrocarbon evaporation and methanol-assisted particle purification from a surfactant. Fcc Pd nanoparticles of 6, 8, 11, and 13 nm in diameter were isolated from water/ AOT/isooctane mixture and used to study a size effect during solvent-free hydrogenation of 2-methyl-3-butyn-2-ol to 2-methyl-3-buten-2-ol. The initial TOF calculated per mole of surface palladium atoms was duplicated when particle size was increased from 6 to 13 nm but remained constant when accounted per number of specific Pd atoms on Pd(111) facets. Selectivity to olefinic alcohol was not size-dependent, but an increase in particle size decreased the byproduct ratio of dimers to saturated alcohol. Acetylenic alcohol hydrogenation is shown to be a structure-sensitive but size-independent reaction for Pd particles with size of 6-13 nm. The work shows also that the Pd size controlled the reaction rate and the byproduct distribution.

Recent Advances in the Liquid‐Phase Synthesis of Metal Nanostructures with Controlled Shape and Size for Catalysis

“…Another widespread technique for preparation of monodispersed spherical nanoparticles with a controlled size for catalytic applications is a microemulsion (ME) technique (37,(55)(56)(57). Water-in-oil (reverse) ME have been generally used for the synthesis of a variety of ultrafine metal particles (55) but there are also some examples of metal nanoparticle formation in normal microemulsions (oil-in-water) (58).…”

“…Recently, size-controlled synthesis of Pd nanospheres allowed determining structure sensitivity but size independence of MBY hydrogenation (57). The particles under study included spherical monodispersed AOT-stabilized particles of 6, 8, 11, and 13 nm isolated from a reverse microemulsion (57).…”

“…The particles under study included spherical monodispersed AOT-stabilized particles of 6, 8, 11, and 13 nm isolated from a reverse microemulsion (57). The unsupported particles were used, and their initial activity and selectivity were correlated with surface atom statistics.…”

“…However, the apparent size sensitivity of MBY hydrogenation disappeared when TOFs were recalculated per number of C atoms on (111) facets, i.e., atoms surrounded by 9 nearest neighbors with 3 missing ones (40). These atoms were proposed to be the active sites for the reaction performed over the AOT-stabilized Pd nanospheres (57). Alkene selectivity did not depend on the particle size, while the by-product distribution varied (57) in the same manner as for Pd catalysts in 1,3-butadiene hydrogenation (101): the more atoms are located on Pd(111) facets, the lower the ratio of isomerization to the saturated products.…”

“…Another method involved the hydrocarbon evaporation in vacuum at 50uC, followed by the surfactant dissolution in methanol with the simultaneous flocculation of Pd nanoparticles, which could be isolated by centrifugation (Fig. 33) (57). The obtained precipitate was shown to contain Pd nanoparticles with the initial size.…”