H₂ Reactions on Palladium Clusters

Abstract

Adsorption of an H2 molecule on Pd(N) clusters (N = 2-4, 7, 13, 19, and 55) is investigated using density functional theory with the hybrid PBE0 functional. Low-energy Pd(N) isomers, taken from a large pool of candidate structures for all cluster sizes (except N = 55), are used in systematic searches for the most stable Pd(N)H2 (molecular) and Pd(N)2H (dissociative) adsorption complexes. Molecular adsorption of H2 is found to occur strictly at atop sites, with the strongest binding typically occurring at the site with the smallest coordination. Binding of dissociated H atoms occurs preferentially on 3-fold faces and on certain favorable edge sites, while binding at atop sites is unstable. Dissociative adsorption is energetically preferred to molecular adsorption for all cluster sizes. The dissociative adsorption energy decreases with cluster size, with pronounced variations due to cluster size effects for the smallest clusters. Adsorption reaction pathways are computed for cluster sizes up to N = 13. Molecular adsorption is found to be barrierless in all cases. Dissociative adsorption occurs without a barrier for the pathways studied for N = 7 and 13 and with a small barrier on the smaller clusters. Finally, lowest-energy pathways for the migration of a dissociated hydrogen atom between local minima on a cluster surface are computed for the Pd4, Pd7, and Pd13 clusters. Calculated migration barriers range from 0.05 to 0.25 eV.

Theoretical study of CO2 hydrogenation to methanol on isolated small Pd clusters

“…This study only evaluates the CO 2 adsorption and hydrogenation reaction on three small size Pd clusters, namely Pd 7 , Pd 9 , and Pd 13 , whose initial conformations are taken from ref [33] . Such stable supported subnanometer Pd x and Pt x has been successfully fabricated experimentally using the soft-landing method [43,44] .…”

“…Such stable supported subnanometer Pd x and Pt x has been successfully fabricated experimentally using the soft-landing method [43,44] . These clusters are chosen for the current study because: ( 1 ) they can effortlessly dissociate H 2 molecule [33] and (2) their size are big enough to accommodate adsorption sites for both CO 2 molecule and H atom. The optimized structures of these Pd x clusters are given in Section 1 of ESI.…”

“…These conditions might be realized in the Pd site of Pd/Oxide system if small size Pd x clusters are used instead of large size Pd islands. Several density functional theory (DFT) studies show that small size Pd x clusters ( x ≤ 13) can easily adsorb and dissociate H 2 molecule [31][32][33][34] . This condition fulfill one of the requirement for CO 2 hydrogenation center.…”

Reactivity of Gold Clusters in the Regime of Structural Fluxionality

“…Some attempts to overcome this problem have recently been made for investigation of H 2 reactions on palladium clusters, where a large pool of low-energy Pd n isomers was considered for a systematic search of the most stable Pd n H 2 (molecular) and Pd n 2H (dissociative) adsorption complexes. 69 However, only the most stable configurations have been considered for investigation of the reaction barriers. The importance of fluxionality and ensemble effects on dissociation of H 2 on gold clusters has been reported by Barrio et al; 53 however, in spite of the intensive investigations on catalytic activity of gold clusters in the past decade, the role of the fluxionality effects on various chemical processes on the cluster surface remains unclear and has yet to be fully understood.…”

Structures, Stabilities, and Electronic Properties of Small-Sized Zr2Si n (n=1–11) Clusters: A Density Functional Study

“…In the past few decades, the binary clusters have aroused considerable interest [1][2][3][4][5][6]. Silicon is a semiconductor element of great importance for applications in microelectronic technology and material science, and silicon clusters have been extensively investigated both experimentally and theoretically [7][8][9][10][11][12][13].…”