Acetylene and Ethylene Hydrogenation on Alumina Supported Pd-Ag Model Catalysts

Abstract

Adsorption and co-adsorption of ethylene, acetylene and hydrogen on Pd-Ag particles, supported on thin alumina films, have been studied by temperature programmed desorption (TPD). The TPD results show that adding of Ag to Pd suppresses overall hydrogenat ion activity but increases selectivity towards ethylene, i.e. similar to that observed on real catalysts. The results are rationalized on the basis of a complex interplay between surface and subsurface hydrogen species available in the system, whereby the latter species are the most critical for total hydrogenation of acetylene to ethane.

Palladium–gallium intermetallic compounds for the selective hydrogenation of acetylenePart II: Surface characterization and catalytic performance

“…The hydrogenation pathway from acetylene to ethylene and further to ethane (reactions 1-3) does not require assemblies of active sites in contrast to the oligomerisation reaction (4) leading to higher hydrocarbons [15,42,43]. Higher hydrocarbons can be dehydrogenated to form carbon deposits and, thus, deactivate the catalyst [44][45][46][47][48][49].…”

Distinguishing surface adsorbed hydrogen from bulk-dissolved hydrogen in supported Pd nanoparticles using in situ Pd L3-edge XANES

“…The hydride has higher mobility than the surface hydrogen and can hydrogenate surface adsorbates upon emerging to the surface [3]. Thus, the amount of bulk-dissolved hydrogen seriously affects the activity and selectivity of structure-sensitive hydrogenation reactions [4].…”

“…The hydride has higher mobility than the surface hydrogen and can hydrogenate surface adsorbates upon emerging to the surface [3]. Thus, the amount of bulk-dissolved hydrogen seriously affects the activity and selectivity of structure-sensitive hydrogenation reactions [4].Geometrical and electronic information of palladium nano-particles and of palladium hydride can be obtained from X-ray absorption spectroscopy (XAS) at the K and L edges [5,6]. At the Pd K edge XAS, the formation of palladium hydrides was generally deduced from an increased interatomic distance in EXAFS analysis [5].…”

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

“…Some Pd facets (e.g., 111) are not prone to carbon dissolution, so hydrogen dissolved in the nanoparticle leads to unselective full hydrogenation. Temperature-programmed desorption (TPD) studies have confirmed that sub-surface hydrogen species lead to non-selective hydrogenation, while surface ones selectively hydrogenate alkynes to alkenes [32]. In addition, according to DFT calculations, the carbide phase affects reaction energeticsonly surface hydrogen adsorption is exothermic, but bulk hydrogen dissolution is suppressed in the presence of Pd-C [33].…”

“…These catalysts produced no alkanes at all, but, instead, significant amounts (up to 70%) of undesired oligomers were formed. Ota et al [25] compared Pd [39,40]. The intermetallic catalyst showed a selectivity of 70% as opposed to 20% for Pd catalyst.…”