First principles investigations of Pd-on-Au nanostructures for trichloroethene catalytic removal from groundwater

Abstract

Catalytic groundwater remediation from chlorinated organic solvents like trichloroethene (TCE) has been found to be more effective and sustainable than traditional non-destructive methods. Among the experimentally studied catalyst materials, Pd-decorated Au nanoparticles show the highest activity and selectivity combined with the best resistance towards poisoning by chemicals present in groundwater. In this study the thermochemistry and adsorption geometries of TCE and its hydrodechlorination products are investigated via density functional theory calculations. Various model systems for Pd-supported Au nanoparticles are addressed. The adsorption of TCE is endothermic on bare Au(111), almost thermoneutral or slightly exothermic on Pd-Au surface alloys and clearly exothermic on Pd overlayer structures on Au(111). The strongest chemisorption is on the di-σ configuration between Pd atoms over the smallest 2D Pd clusters containing only a few Pd atoms. These are not, however, the best catalysts as they are too small to co-adsorb hydrogen needed for hydrodechlorination reaction. We demonstrate good correlation between adsorption energies and the d-band center of the system. The variation of adsorption energy from the one Pd-Au composition to the other can be tentatively assigned to be due to the ligand and coordination effects. Also, the ensemble effects are important; without the right ensemble the adsorption is weak or endothermic.

Hydrogen adsorption on and spillover from Au- and Cu-supported Pt3 and Pd3 clusters: a density functional study

“…For brevity, we refrain from presenting detailed comparisons. Our results also agree with those of previous calculations addressing the adsorption of atomic hydrogen on Pd clusters 12,13,35,56 on Au(111), within 10 kJ mol À1 for DE ads . The same holds for the adsorption of atomic hydrogen on Pd atoms embedded in Cu(111).…”

“…Cross comparison of the four types of systems studied -Pt 3 /Au, Pd 3 /Au, Pt 3 /Cu, and Pd 3 /Cu -will bring insight into adsorption properties not previously offered; note that earlier computational studies essentially focused on the systems Pd/Au. 12,13,35,36 Electrolyte effects have not been considered in the present work. However, the adsorption energy of hydrogen is only slightly affected by the electrolyte solution.…”

Hydrogen Adsorption on Au-Supported Pt and Pd Nanoislands: A Computational Study of Hydrogen Coverage Effects

“…In this regard, various density functional theory (DFT) calculations have been performed to study the adsorption of hydrogen on Pd ,,,,,,, and Pt ,, nanoislands supported on Au(111). The results of these calculations reveal that there are multiple stable adsorption sites for hydrogen on Pd and Pt nanoisland on Au(111) under the low-coverage condition of adsorbed hydrogen.…”

“…The results of these calculations reveal that there are multiple stable adsorption sites for hydrogen on Pd and Pt nanoisland on Au(111) under the low-coverage condition of adsorbed hydrogen. The identified adsorption sites include the hollow sites (hydrogen is 3-fold coordinated), the bridge site (hydrogen is 2-fold coordinated), and the sites at the Pt/Au and Pd/Au boundaries (rim sites). ,,− ,, However, one key factor for an ideal HOR/HER electrocatalysts is to have a free energy of hydrogen adsorption near zero, Δ G (θ H ads ) ≈ 0. ,− Δ G (θ H ads ) is a function of the coverage of adsorbed hydrogen θ H ads . ,− Furthermore, experimental and computational results indicate that HOR/HER at low overpotential on Pt electrodes, for instance, take place under high coverage condition of spectator adsorbed hydrogen. ,,− Therefore, the active sites for HOR/HER on Pt and Pd nanoislands supported on Au(111) are likely metal sites with preadsorbed hydrogen atoms.…”

Chloroform Hydrodechlorination over Palladium–Gold Catalysts: A First‐Principles DFT Study

“…performed DFT calculations for chloroform HdCl reaction over the Pd(1 1 0) surface . Honkala and co‐workers conducted DFT‐based studies for the HdCl reaction on Pd–Au catalysts of trichloroethene . To our knowledge, no first‐principles study has been conducted for chloroform HdCl on Pd–Au bimetallics.…”