A benchmark database for adsorption bond energies to transition metal surfaces and comparison to selected DFT functionals

Better catalysts and electrocatalysts are essential for the production and use of clean fuels with less pollution and improved energy efficiency, for making chemicals with less energy and environmental impact, for pollution abatement, and for many other future technologies needed to achieve environmentally friendlier energy supply and chemicals industry. Crucial for rational design of better catalyst and electrocatalyst materials is knowledge of the energies of elementary chemical reactions on late transition metal surfaces. This knowledge would also aid in designing more efficient and stable photocatalysts and batteries for harvesting and storing solar energy. These are all crucial for sustainable living with high quality. Herein, I review measurements of surface reaction energies involving many of the most common adsorbates formed as intermediates on late transition metal surfaces in catalytic and electrocatalytic reactions of interest for energy and environmental technologies. I focus on calorimetric measurements of the heat of molecular and dissociative adsorption of gases on single crystals (i.e., single crystal adsorption calorimetry, or SCAC) that allow the heats of formation of adsorbed intermediates in well-defined structures to be directly determined. Adsorption reactions are often irreversible, and in such cases SCAC is required to get these heats, since the other methods for measuring adsorption energies (equilibrium adsorption isotherms and temperature-programmed desorption) work only for reversible adsorption. Common examples of irreversible adsorption reactions are ones that produce adsorbed molecular fragments or adsorbed molecules such as olefins and aromatic molecules that bind very strongly to non-noble metals. When the heats of formation of different adsorbed molecular fragments are compared to each other, and to their values on different metal surfaces, they reveal which properties of the metal surface and the molecular fragments determine metal-adsorbate bond strengths, and clarify differences in catalytic reactivity between different metals. When combined with earlier adsorption energy measurements, these heats also provide a database of reliable energies of adsorbed catalytic intermediates that serve as crucial benchmarks to guide the development of improved computational methods for calculating the energetics of elementary steps on late transition metal surfaces (i.e., reaction energies and activation barriers), such as density functional theory. The energy accuracy of such computational estimates is crucial for the future of catalysis research and catalyst discovery.

ABSTRACTThe adsorption properties of organic phosphines on transition metal (TM) surfaces (Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au) have been studied to explore the possibility of building novel heterogeneous chiral catalytic systems based on organic phosphines. Preferred adsorption sites, adsorption energies and surface electronic structures of a selected set of typical organic phosphines adsorbed on TM surfaces are calculated with density-functional theory to obtain a systematic understanding on the nature of adsorption interactions. All organic phosphines considered are found to chemically adsorb on these TM surfaces with the atop site as the most preferred one, and the TM–P bond is formed via the lone-pair electrons of the P atom and the directly contacted TM atom. These findings imply that it is indeed possible to build heterogeneous chiral catalytic systems based on organic phosphines adsorbed on TM surfaces, which, however, requires a careful design of molecular structure of organic phosphines.

Dissociation of O2 into atomic oxygen is a significant route for O2 activation in metal-catalyzed oxidation reactions. In this study, we systematically investigated the mechanisms of O2 dissociation and the promoting role of water on nine transition metal (Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, and Au) surfaces. It was found that on clean metal surfaces, the dissociation of O2 was most favorable on Co(0001) and most difficult on Au(111), according to the free energy barriers of Co (0.03 eV) < Rh (0.20 eV) < Ni (0.26 eV) < Cu (0.45 eV) < Ir (0.62 eV) < Pd (0.65 eV) < Pt (0.92 eV) < Ag (1.07 eV) < Au (2.50 eV). With the involvement of water, O2 and H2O formed an O2H2O complex via hydrogen bonding interactions, being accompanied by an increased co-adsorption free energy of 0.17-0.52 eV and a more activated O-O bond. More importantly, the introduction of water reduced the barriers of O2 dissociation on all the nine metal surfaces, with the reduction of the free energy barrier ranging from 0.03 eV on Co(0001) to 1.05 eV on Au(111). The intrinsic reasons for the promotional role of water are attributed to the hydrogen bonding effect between O2 and H2O and the electronic modification effect induced by the water-surface interaction. These results provide a fundamental understanding of the catalytic role of water in O2 dissociation on the transition metal surfaces and may be helpful in the rational design of new efficient catalysts for the oxidation reactions using molecular oxygen or air.

Hydrogen adatoms are involved in many reactions catalyzed by Transition Metal (TM) surfaces, such as the Haber-Bosch process or the reverse water gas shift reaction, key to our modern society. Any rational improvement on such a catalyst requires an atomistic knowledge of the metal↔hydrogen interaction, only attainable from first-principles calculations on suited, realistic models. The present thorough density functional theory study evaluates such H interaction at a low coverage on most stable surfaces of bcc, fcc, and hcp TMs. These are (001), (011), and (111) for bcc and fcc TMs and (0001), (101̅0), and (112̅0) for hcp, covering 27 TMs and 81 different TM surfaces in total. In general terms, the results validate, while expanding, previous assessments, revealing that TM surfaces can be divided into two main groups, one in the majority where H2 would be thermodynamically driven to dissociate into H adatoms, located at heights of ∼0.5 or ∼1.0 Å, and another for late TMs, generally with a d 10 electronic configuration, where H2 adsorption with no dissociation would be preferred. No trends in H adsorption energies are found down the groups, but yes along the d series, with a best linear adjustment found for the d-band center descriptor, especially suited for close-packed fcc and hcp TMs surfaces, with a mean absolute error of 0.15 eV. Gibbs free adsorption energies reveal a theoretical volcano plot where fcc TMs are best suited, but with peak Pt performance displaced due to dispersive force inclusion in the method. Still, the volcano plot with respect to the experimental logarithm of the exchanged current density polycrystalline data is far from being valid for a quantitative assessment, although useful for a qualitative screening and to confirm the trends computationally observed.

In this work, we report a density functional theory study of nitric oxide (NO) adsorption on close-packed transition metal (TM) Rh(111), Ir(111), Pd(111) and Pt(111) surfaces in terms of adsorption sites, binding mechanism and charge transfer at a coverage of Theta(NO) = 0.25, 0.50, 0.75 monolayer (ML). Based on our study, an unified picture for the interaction between NO and TM(111) and site preference is established, and valuable insights are obtained. At low coverage (0.25 ML), we find that the interaction of NO/TM(111) is determined by an electron donation and back-donation process via the interplay between NO 5sigma/2pi* and TM d-bands. The extent of the donation and back-donation depends critically on the coordination number (adsorption sites) and TM d-band filling, and plays an essential role for NO adsorption on TM surfaces. DFT calculations shows that for TMs with high d-band filling such as Pd and Pt, hollow-site NO is energetically the most favorable, and top-site NO prefers to tilt away from the normal direction. While for TMs with low d-band filling (Rh and Ir), top-site NO perpendicular to the surfaces is energetically most favorable. Electronic structure analysis show that irrespective of the TM and adsorption site, there is a net charge transfer from the substrate to the adsorbate due to overwhelming back-donation from the TM substrate to the adsorbed NO molecules. The adsorption-induced change of the work function with respect to bare surfaces and dipole moment is however site dependent, and the work function increases for hollow-site NO, but decreases for top-site NO, because of differences in the charge redistribution. The interplay between the energetics, lateral interaction and charge transfer, which is element dependent, rationalizes the structural evolution of NO adsorption on TM(111) surfaces in the submonolayer regime.

Promotional effects of chemisorbed oxygen and hydroxide in the activation of C–H and O–H bonds over transition metal surfaces

Our knowledge of water bonding on metal surfaces is ruled by the coexistence of covalent and electrostatic nature in water-metal interactions, which leads to the well-known, preferred flat geometry on transition metal surfaces. Using density functional theory (DFT) calculations, herein we have shown that this picture has to be modified for water bonding on Sc(0001), Y(0001), and La(0001), where upright water orientation has been surprisingly found to preferentially coexist with the flat geometry on the rare-earth metal surfaces. Our investigations have proved that both water orientations on the rare-earth metal surfaces originate from unique bonding mechanisms that do not exist in water adsorption on any late transition metal surfaces. In this unique bonding picture, covalent components are evidently absent in the water-metal interactions, which are overwhelmingly dominated by the first-order quantum electrostatics featured by two nearly separated potential wells in the water-metal bonds and by the second-order quantum electrostatics featured by alternating charge depletion and accumulation regions in interference. The new picture not only advances our understanding of how water makes bonds with earlier transition metal surfaces but also lays a physical basis for improving catalytic performance of the rare-earth-metal-based green catalysts for clean energy.

Unenhanced susceptibilities near (001) surface are calculated for semi-infinite fcc transition metals and compared with those for bulk (infinite) metals on the basis of the tight binding model which takes into account five d -orbitals. Calculated surface susceptibilities as the function of the number of d -electrons are considerably enhanced in the nearly half-filled region and reduced in the nearly filled region. In the light of the calculation, magnetic properties near surface of transition metals are discussed.

We propose a model for CO chemisorption on late transition metal, noble metal, and main-group surfaces based on the results of energy partitioning studies of surface -CO bonding for the CO/M(111), M)Pt,Cu,Al chemisorption systems. Plane-wave density functional theory was used to calculate the chemisorption geometry for CO on the top, bridge, and hollow sites of the M(111) (M)Pt,Cu,Al) surfaces and to verify the experimentally determined preference for top site CO chemisorption on all three surfaces. To construct a chemically intuitive, molecular orbital based model of surface-CO bonding, an energy partitioning analysis of surface-CO bonding was carried out within a tight binding scheme based on the extended Huckel method. Although within this one-electron formalism we are no longer able to make quantitative assesments of bonding, we are able to readily extract surface-CO bonding trends. By expanding the orbital basis on CO to include energetically low-lying nonfrontier orbitals and explicitly evaluating the role of the surface s and p bands in surface-CO bonding, we note several discrepancies between our model and traditional, frontier orbital based models of surface-CO interaction. Especially important is the role of the CO(4U) orbital. We note that for CO chemisorption on all three surfaces, the energetic preference for top site chemisorption is the result of a balance between the stabilization associated with the formation of the surface -CO bond and chemisorption- site-dependent changes in both C-O bonding and M- M( M)Pt,Cu,Al) bonding within the surface layer on chemisorbing CO. Further, by choosing to consider CO chemisorption on the Cu(111) surface as part of a continuous transition from CO chemisorption on late transition metal surfaces to CO chemisorption on sp- metal surfaces, we are able to assess the degree to which we may refer to copper as an sp-metal.

In recent years, evaluating the effect of van der Waals (vdW) forces for many physical systems, including the adsorption of small organic molecules on metal surfaces, became possible thanks to the continuous improvements in vdW density functional theory (DFT). In this work, employing the vdW-DF (revPBE-vdW), the optimized vdW-DF (optB88-vdW, optPBE-vdW, optB86b-vdW), and vdW-DF2 (rPW86-vdW2) methods, we study the adsorption of benzene on a range of (110) transition metal surfaces. We evaluate the performance of the vdW functionals by examining the equilibrium adsorption geometries and energies and comparing the results with the available experimental data and the PBE calculations. Our results show that the optimized vdW-DF functionals predict the equilibrium geometries in good quantitative agreement with some of the available experimental reports. We show the crucial importance of the vdW interactions for accurate description of equilibrium geometries and energies of benzene on transition metal (110) surf...

Linear scaling of charge transfer versus work function of Ammonia chemisorption on X-metal (X = Ag, Au, Pd, and Pt) surface

Chemical effects on vibrational properties of adsorbed molecules on metal surfaces: Coverage dependence

This Letter compares the efficiency of the conversion of CO to C2 species (ethanol and ethylene) on nine late transition metal (100) surfaces (Co, Ni, Cu, Rh, Pd, Ag, Ir, Pt, Au) by means of reaction onset potentials calculated using density functional theory and atomistic thermodynamics. Due to adsorption–energy scaling relations, one can model trends in limiting potentials using only two descriptors, namely *C2O2 and *OH binding energies. The resulting activity plots (i) outline the binding properties of optimal catalysts, (ii) show little dependence of the overpotential on adsorption energies, especially on the weak-binding regime, and (iii) explain why Cu(100) reduces CO to ethylene at low overpotentials. Surprisingly, CO reduction to ethanol is predicted to be thermodynamically favorable on Ag(100). This points toward existing experimental results and calls for detailed studies of the conditions necessary to enhance CO electroreduction to ethanol using Ag and its alloys.

The DFT/vdW-WF2s1 method, recently developed to include the van der Waals interactions in the density functional theory and describe adsorption processes on metal surfaces by taking metal-screening effects into account, is applied to the case of the interaction of Xe and graphene with a transition-metal surface, namely, Ni(111). In general, the adsorption of rare-gas atoms on metal surfaces is important because it is prototypical for physisorption processes. Moreover, the interaction of graphene with Ni(111) is of great interest for practical applications, for instance concerning the efficient and large-scale production of high-quality graphene; from a theoretical point of view, it is particularly challenging, since it can be described by a delicate interplay between chemisorption and physisorption processes. The first-principles simulation of transition metals requires particular care also because they can be viewed as intermediate systems between simple metals and insulating crystals. Even in these cases the method performs well as demonstrated by comparing our results with available experimental data and other theoretical investigations. We confirm that the rare-gas Xe atom is preferentially adsorbed on the top-site configuration on the Ni(111) surface too. Our approach, based on the use of the maximally localized Wannier functions, also allow us to well characterize the bonds between graphene and Ni(111).

The study of alkali-metal adsorption on metal and semiconductor surfaces has been a favored topic of surface science. This is motivated by a number of interesting physical effects, such as charge transfer, work function changes, and alteration of surface reactivity. Despite considerable research efforts, however, there has still been significant controversies about most of these properties. In this paper, a review is presented concerning alkali–metal adsorption on well-defined transition-metal and semiconductor surfaces, with particular emphasis on the bond-nature analysis using low-energy D + scattering. The analysis based on resonance neutralization of the D + ions associated with the 1s hole diffusion into the band reveals that Na, K, and Cs adatoms have significant covalency on the transition metal surfaces while those except for Na are ionically adsorbed on the semiconductor surfaces in a small coverage regime (&lt; 1.7 × 1014 adatoms/cm 2). The charge state of Na is rather critical because of the larger ionization energy than the others. The other examples are concerned with the analyses of the interaction of these alkali–metal adatoms with electronegative species such as oxygen and halogens on the metal and semiconductor surfaces.