Rational design of a heterogeneous palladium catalyst for the selective hydrogenation of alkynes

Abstract

terium chemisorption. The catalysts were prereduced in D2 for 3-4 h at room temperature in a standard gas titration apparatus. They were then evacuated under vacuum (1CT1 234 mbar) overnight at 270 °C to yield the zero-valent clean metal surface. Deuterium was chosen over hydrogen to avoid the ,3-hydride phase formation and the deuterium titrations were performed with the catalyst heated to 100 °C as a further measure to avoid deuterium absorption in to the Pd bulk.24 Electron Microscopy Studies. The powdered Pd/CaC03 catalysts were crushed by an agate mortar and dispersed into suspension by shaking in ethanol. A drop of suspension was placed on a holey-carbon grid and allowed to dry. These specimens were examined in a JEOL JEM-200CX high resolution as well as in an analytical transmission electron microscope.Auger Electron Spectroscopy. The Auger electron spectroscopic studies were obtained from the Charles Evans & Associates Materials Characterization Laboratories in Redwood City.General Hydrogenation Procedure. Hydrogenations were carried out at ambient conditions in a three-necked round-bottom flask connected to a hydrogen reservoir maintained at normal pressure. The catalysts were placed in the flask and flushed (24) Benson,

Palladium Nanoparticles Suspended in an Ionic Liquid as Reusable Catalyst for Alkyne Semihydrogenation

“…The surface structure of a fcc metal particle is essentially composed of three different types of surface atoms that are characterized by the number of nearest neighbor atoms. 42 These are the terrace atoms with nine nearest neighbours, step atoms with seven and corner or kink atoms with six or less neighbours. The relative distribution and number of these surface atoms changes with particle size.…”

The Reduction of Alkynes Over Pd-Based Catalyst Materials - A Pathway to Chemical Synthesis

“…semi-hydrogenation selectivity is to add CO to the reaction system, which is believed to displace alkene from the adsorption sites of Pd [14,21], although studies have shown that hydrogenation could be reasonably selective (>80%) even on Pd foils without modifications [22,23]. Many authors believe that alkynes adsorb more selectively on a metal surface, retarding alkene adsorption and hindering its hydrogenation to alkane, while alkynes are present in the reaction mixture [17,24].…”

“…Ulan et al studied the activity of unsupported Pd catalysts in 2-hexyne hydrogenation in hexane under ambient pressure [22]. Pd single crystals and polycrystalline foils were compared and it was shown that terrace Pd surfaces represented the most selective sites for cis-alkene formation.…”

“…Second, compounds such as quinoline or pyridine-comprising polymers are used. These substances are believed to block most of the adsorption sites decreasing alkene adsorption due to steric or electron-doping effects of nitrogen [7,22,33,34]. Gislason et al have performed kinetic simulations of acetylene hydrogenation in ethylene flow under industrial conditions [12].…”

The Wilkinson Complex as a Heterogeneous Catalyst in the Partial Hydrogenation of 1-Heptyne. Regeneration of the Complex

“…1 In this respect, the Lindlar catalyst (Pd/CaCO 3 modified with Pb(OAc) 2 ) proved to be useful for the hydrogenation of almost any triple bond to double bond, or reduction of doubly substituted acetylenes giving cis olefins. 2 Alternatively, along the years, the use of transition metal complexes has become increasingly important as catalysts for such reactions, both in homogeneous and heterogeneous systems.…”