Theoretical insight of nitric oxide adsorption on neutral and charged Pd_n (n = 1–5) clusters

Abstract

Density functional theory (DFT) calculations within the framework of generalized gradient approximation have been used to systematically investigate the adsorption of nitric oxide (NO) molecule on neutral, cationic, and anionic Pd n (n 5 1-5) clusters. NO coordinate to one Pd atom of the cluster by the end-on mode, where the tilted end-on structure is more favorable due to the additional electron in the p* orbital. On the contrary, in the neutral and cationic Pd 2 system, NO coordinates to the bridge site of cluster preferably by the side-on mode. Charge transfer between Pd clusters and NO molecule and the corresponding weakening of NAO bond is an essential factor for the adsorption. The NAO stretching frequency follow the order of cationic > neutral > anionic. Binding energy of NO on anionic clusters is found to be greater than those of neutral and cationic clusters.

The Effect of Gamma-Al2O3Support on the NO Adsorption on Pd4Cluster

“…Previous studies reported that the NO adsorption process happens with charge back-donation from the Pd 4 cluster to the NO molecule. 21 Our results indicate that the amount of charge transferred between the two moieties depends on the adsorption site, but not on the arrangement. In both arrangements, adsorption in the atop mode, where back-donation to the 2π* orbital of NO seems to be less efficient, results in charge transfer from the NO molecule to the Pd 4 cluster, while for adsorption in the bridge and hollow modes, charge is transferred from the Pd 4 cluster to the NO molecule.…”

“…Recent studies proposed adsorption either on the atop 21 or on the hollow and bridge sites, 46 following previous computational studies that also suggested threefold hollow 47 or threefold hollow plus atop sites as the preferential adsorption mode. 48 In the present study, we computed the adsorption of NO on three different Pd 4 clusters, planar (Figure 1b), tetrahedral ( Figure 1c) and the distorted cluster obtained after optimization of Pd 4 over the γ-alumina surface (Figures 1f and 1g).…”

“…13 The adsorption of NO on the supported catalyst surface has been investigated by both experimental 7,[14][15][16][17][18][19][20] and theoretical procedures. [21][22][23][24][25][26][27][28][29] NO adsorbs on small Pd clusters through its nitrogen atom in a tilted orientation, preferentially in the hcp threefold and bridge sites, 27 although the relative binding energies are strongly dependent on the size and geometry of the cluster employed. 27 For adsorption of NO on an extended surface at low coverage the interaction is determined by electron donation and back-donation involving the 5σ/2π* antibonding orbital of the NO molecule and the d-bands of the transition metal, with a net charge transfer from the transition metal to the adsorbed NO.…”

“…In the vast literature on theoretical studies of NO adsorption on metal surfaces, the catalyst is frequently represented as a single crystal 29 or as a small atomic cluster, [21][22][23][24]27,28 although evidence shows that the support Vol. 27, No.…”

Transformation of Bulk Pd to Pd Cations in Small-Pore CHA Zeolites Facilitated by NO

“…Periodic DFT calculations, combined with ab initio thermodynamics analysis, were used to figure a phase diagram to predict plausible Pd species at relevant partial pressures and temperatures. 59,60 The following equilibrium reaction was considered (eq 2): 62,63 The structural information (CONTCAR files) of all the considered structures can be found in the SI. Note that the simulated XANES spectrum for the optimized Z[Pd] structure is similar to the experimental one for Pd imp /CHA(H 2 _NO) (Figure S5), confirming that our model is reasonable as Pd 2+ cations in CHA zeolites.…”