Chemisorption and thermal decomposition of ethylene on Pd(110): Electron energy loss spectroscopy, low-energy electron diffraction, and thermal desorption spectroscopy studies

Abstract

The adsorbed state of ethylene on Pd(110) at 90 K and its thermal decomposition in the temperature region between 90 and 600 K have been studied by the use of high resolution electron energy loss spectroscopy (EELS), low-energy electron diffraction (LEED), and thermal desorption spectroscopy (TDS). At 90 K, ethylene is π bonded to the Pd(110) surface and is adsorbed almost disorderedly. The c(2×2)-C2H4 patches are formed near the saturation coverage (which corresponds to 0.58 C2H4 molecule per surface Pd atom). By heating the C2H4-saturated Pd(110) surface to 260 K, some C2H4 admolecules are desorbed intact and the remaining admolecules rearrange their adsorbed sites to form the c(2×2)-C2H4 structure. At above 300 K, almost all the C2H4 admolecules are dehydrogenated, and the ethynyl (CCH) species, H adatoms and unstable dehydrogenated species [possibly, vinyl (CHCH2) species] are formed; the C2H4 desorption occurs by the recombination of H adatoms and dehydrogenated species. The remaining H adatoms are desorbed as β-H2 at ∼325 K. By heating to 450–520 K, ethynyl is decomposed, and only carbon adatoms remain on Pd(110); the decomposition is accompanied by the H2 desorption. Structural models of chemisorbed C2H4 and CCH on Pd(110) are proposed.

Density Functional Study of Ethylene Adsorption on Palladium Clusters

“…In some cases the change in the cluster size by one metal atom can be accompanied by a large change in the reactivity, and curves like Figure 5 were often found in experiments. We notice that for Pd [3][4][5] clusters, which collapse under the di-σ adsorption, the best adsorption mode is π, whereas the Pd 2 and Pd 6 , which give π and di-σ distortions of the same magnitude, the di-σ adsorption is more favorable.…”

“…However, HREELS experiments support a π adsorption on Pd(111) 2 and Pd(110), 3 whereas for Pd(100) 1 both π and di-σ modes were observed. Table 6 also shows the spin state of the C 2 H 4 Pd n complexes.…”

“…For Pd n (n ) 3-5) clusters, the bond between the two Pd atoms involved in the adsorption is broken (see Figure 4). Ethylene induces a reconstruction of the clusters: from the triangle toward the linear structure for Pd 3 and from the tetrahedron toward the planar structure for Pd 4 . Such effects were already suggested by Parks et al 16 for N 2 adsorption on Ni n clusters.…”

Alkene chemistry on the palladium surface: nanoparticles vs single crystals

“…The reactions of ethene with metal surfaces have been investigated on both single crystals and supported catalysts (see reviews of Zaera [6], and Sheppard and De La Cruz [7,8]). As Pd catalysts typically show high activities and selectivities, a considerable research effort has been devoted to studying surface reactions on Pd, employing infrared reflection absorption spectroscopy (IRAS), temperature-programmed desorption (TPD), high-resolution electron (and photoelectron) spectroscopy (HREELS, PES), and ab initio calculations [9][10][11][12][13][14][15][16][17][18][19].…”

The Adsorption of Acetylene and Ethylene on Transition Metal Surfaces

“…Several experimental studies of the adsorption of ethylene on palladium surfaces have been found on the literature [47][48][49]. According with these studies on the (111) and (110) surfaces, the ethylene molecule adsorbs preferably in the In the only known experimental studies on the adsorption of on a Pd(l00) surface, at low temperatures, Stuve et al [64,65] using TPRS and EELS concluded that both and forms are stable and coexist on this surface at 80 K. Table 8 lists the results obtained for adsorbed on a Pd(l00) surface on the and adsorption modes.…”