Surface Heterogeneity of Supported Palladium Catalyst for the Hydrogenation of Acetylene−Ethylene Mixtures

Abstract

The hydrogenation of acetylene−ethylene mixtures over a Pd/α-Al2O3 catalyst was studied. Kinetic investigations were carried out in a flow system equipped with a gradientless microreactor over a wide range of acetylene and ethylene partial pressures. Three types of active sites were thus identified: A 1 and A 2 sites which are highly selective in the hydrogenation of acetylene to ethylene via a mechanism involving the competitive (A 1 ) and noncompetitive (A 2 ) adsorption of acetylene and hydrogen, and E sites which are active only for the hydrogenation of ethylene. E sites are able to adsorb acetylene, an effect which strongly inhibits ethane formation. The above three types of active sites are very likely created on the palladium surface by carbonaceous deposits formed during the stabilization process. The identified sites determine the selectivity of the catalyst and manifest themselves in kinetic investigations depending on the process conditions.

Selective hydrogenation of acetylene on SiO2 supported Ni-In bimetallic catalysts: Promotional effect of In

“…However, Kim et al [55] consider that the relatively light green oil on or in the vicinity of the Pd surface only slightly decreased the catalytic activity. They attributed this to the hydrogen transfer mechanism, that is, the carbonaceous overlayer worked as a medium to allow the hydrogen transfer from the Pd surface to acetylene associated with the overlayer [56,57,58,59]. Accordingly, the acetylene hydrogenation rate was unaffected by the large amounts of relative light green oil.…”

Unusual Catalytic Performance for Selective Acetylene Hydrogenation over Pd Nanoparticles Fabricated on N,O-containing Organic Groups Modified Silica

“…It is well known that the adsorption capability of the acetylene is much stronger than the ethylene on the Pd catalyst [40], so the alkyne molecules can present on the surface of the catalyst in a high coverage ratio by displacing the alkene molecules from the surface of the catalyst or blocking their readsorption before all alkyne molecules are consumed virtually. In addition, the low H 2 pressure may favor the formation of small Pd sites due to deposition carbonaceous species on Pd surface, which permit the selective hydrogenation of acetylene but simultaneously inhibit the adsorption of ethylene [41]. Therefore, in normal case, high ethylene selectivity was obtained at low acetylene conversion and low H 2 /C 2 H 2 ratio.…”

Propyne hydrogenation over alumina-supported palladium and platinum catalysts

“…Duca et al have examined ethyne and ethene hydrogenation over palladium catalysts and, upon consideration of geometrical effects determined by steric hindrance of the surface species present, propose a multi-site model with a degree of exchangeability between the sites [17,18]. Borodzinski and Golebiowski [19], and Borodzinski [20] has extended these concepts and invokes a two-site model similar to that outlined by Kemball et al [10] to describe the characteristics of mixtures of ethyne and ethene hydrogenated using a supported Pd catalyst. The sites are created by carbonaceous deposits defining large (Site E) and small (Site A) spaces on the palladium surface.…”