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[Display omitted] • CO 2 hydrogenation over inverse supported Zr 9 O 18 /Ni(1 1 1) nanocatalyst was computed. • Charge transfer from Ni(1 1 1) to supported Zr 9 O 18 nanoparticle has been found. • Supported Zr 9 O 18 nanoparticle has coordinatively unsaturated Zr sites at interface. • H 2 prefers dissociative adsorption on Ni(1 1 1) and CO 2 activation prefers interface Zr sites. • Surface HCOO is the most important intermediate and methanol is the selective product. To tune the activity and selectivity of CO 2 hydrogenation, inverse supported Zr 9 O 18 /Ni(1 1 1) catalysts are designed based on ab initio molecular dynamics simulation and density functional theory calculation under the consideration of the number of interfacial O and Zr atoms as well as the interaction between O and Zr atoms. For the most stable catalyst with coordinatively unsaturated interface Zr sites, charge transfer from surface to oxide has been found. The Ni(1 1 1) surface is pre-covered by H atoms and the interface Zr sites can activate CO 2 to a large extent, and their interaction results in the spontaneous formation of surface formate. Further hydrogenation of surface formate leads to the selective formation of methanol with an apparent Gibbs free energy barrier of 0.62 eV, lower than that of methane formation (1.09 eV). On the contrary to metallic nickel and supported nickel catalysts, the most favoured methanol formation route [HCOO → CHO → CH 2 O → CH 3 O → CH 3 OH] does not involve CO as intermediate, revealing the mediated interface effect. [ABSTRACT FROM AUTHOR]

[Display omitted] • Temperature-dependent ethylene dissociative adsorption on ruthenium was computed quantitatively. • Revised PBE can best quantify the adsorption energy of ethylene, H 2 and CO. • Computed activation barriers of the dissociation of CH 2 CH 2 * and CH 3 C* agree quantitively with experiments. • CO co-adsorption stabilizes CH 3 C* by blocking surface sites and raising the dissociation barrier. • BEP relationship is found for the formation of CH 3 C* and HCC under the co-adsorbed CO and hydrogen. The dissociative adsorption of ethylene onto Ru(1 1 1) at different temperatures was computed systematically at the first time. At 105 K, ethylene dissociative adsorption has the co-adsorbed CH 2 C*+2H* and CH 3 C*+H* as the first and second stable surface intermediates. At over 330 K, CH 3 C*+H* is converted back into CH 2 C* accompanied by H 2 desorption and the subsequent dissociation of CH 2 C* into HCC*, HC*+C* and 2C*. The computed Arrhenius activation barriers of the dissociation of CH 2 CH 2 (0.18 vs. 0.22 ± 0.04 eV) and CH 3 C (0.54 vs. 0.52 ± 0.04 eV) agree perfectly with the available experimental values, and CH 3 C* represents the most stable surface species. Under CO co-adsorption, the most stable surface species are the co-adsorbed CH 3 C*+H*+3CO*. It is found that CO co-adsorption promotes H 2 desorption and stabilizes CH 3 C* by blocking the surface sites for dissociation and raises the dissociation barrier compared to the clean surface (0.78 vs 0.54 eV). Brønsted–Evans–Polanyi relationship between the activation Gibbs free energy barrier and reaction Gibbs free energy is found for CH 2 C*+2H*+ n CO* = CH 3 C*+H*+ n CO* and CH 2 C*+2H*+ n CO* = HCC*+3H*+ n CO* (n = 0–3). Ethylene adsorption has di-σ and π adsorption configurations in very close energy, and H 2 has adsorption energy of about 0.90 eV. [ABSTRACT FROM AUTHOR]

Abstract The surface energies and the morphologies of three iron oxides (α-Fe 2 O 3 , Fe 3 O 4 , and FeO) are systematically investigated by Density Functional Theory (DFT) employing PBE and PBE+U methods. The surface energies are computed under various O chemical potential which is directly related to atmosphere condition. Compared with available experimental observations, PBE provides reasonable prediction on surface stability of all three oxides while the results of PBE+U are not well consistent with experiments for Fe 2 O 3. Based on the Wulff construction and calculated surface energies, the micro-crystal morphologies of three iron oxides are predicted at various oxygen chemical potential. Subsequently, on basis of the data of surface energies, the effect of surface free energies on phase equilibrium of iron oxides nanoparticles are investigated. These results suggest that particle sizes of nanometer have a significant influence on the thermodynamic equilibrium shifting due to their large surfaces energies contributions. This principle can guide people control the phase transition of iron oxides by adjusting surface energies contributions by changing the sizes of particles. Graphical abstract Unlabelled Image Highlights • PBE provides more reasonable prediction on surface stability of three iron oxides (α-Fe 2 O 3 , Fe 3 O 4 , and FeO) than PBE+U. • O-terminations are generally more stable than the Fe-terminations over a wide range of Δμ O for three iron oxides. • The Wulff morphology of iron oxides is a function of O chemical potential. • Particle sizes of nanometer have a significant influence on the thermodynamic equilibrium shifting. [ABSTRACT FROM AUTHOR]

[Display omitted] • Real space evidence of p4g(2 × 2) Fe 2 C and Co 2 C surface carbides. • Tip-sample distance dependent STM imaging of Fe 2 C. • Fe 2 X (X = B, C, N, O) with increasing electrons the reconstruction becomes less favourable. Thin FCC (1 0 0) iron and cobalt carbide films were prepared on Cu(1 0 0) to study the connection between their structure, electronic properties and stability. We present the first detailed, real space experimental confirmation of the C-induced clock reconstruction on the FCC(1 0 0) surfaces of iron and cobalt. Both Fe and Co surface carbides show p4g (2 × 2) surface reconstruction with tetracoordinated square planar carbon and pure FCC (1 0 0) metal layers underneath. Combining tip-sample distance dependent STM imaging with theoretical calculations we present different imaging modes of Fe 2 C. Using a combination of angle-resolved x-ray photoelectron spectroscopy (AR-XPS), Auger electron spectroscopy (AES), low energy electron diffraction (LEED), scanning tunneling microscopy (STM), and theoretical calculations we provide detailed electronic and structural models for Fe 2 C and Co 2 C p4g (2 × 2) surface carbides and other 2D Fe 2 X interstitial compound systems. In various Fe 2 X (X = B, C, N, O) surface compounds moving to the right in the periodic table with increasing electrons the reconstruction becomes less favorable, while iron carbide shows the highest stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • CO 2 Conversion to CH 4 and CH 3 OH on ZrO 2 support Ni catalysis was computed. • Metal-Metal and Metal-support Interaction was analysed. • Reaction Mechanisms, differently from metallic Ni, were identified. • Metal interaction determines structure of support Ni and reaction mechanisms. To better understand the metal-support interaction and structure–activity relationship, we computed the mechanisms of CO 2 hydrogenation to CH 4 and CH 3 OH on ZrO 2 supported Ni catalyst. On a supported irregular Ni 13 cluster, which exhibits a balanced metal–metal and metal-support interaction with surface Zr and O atoms covered, two preferred routes [CO 2 → CO → CHO → CH/CH 3 O → CH 3 → CH 4 /CH 3 OH] are found, and the rate-determining step is the CO 2 direct dissociation. Such mechanisms differ very strongly from those reported on flat metallic Ni(1 1 1) surface and Ni clusters supported on different metal oxides, demonstrating that different supports generate different metal-support interaction that simultaneously changes the metal structures and the reaction mechanisms. [ABSTRACT FROM AUTHOR]

[Display omitted] • The morphology evolution of Hägg carbide Fe 5 C 2 under hydrogen conditions was explored. • Carbon-rich facets expose more area surface in Wulff construction with decreasing hydrogen chemical potential, while iron-rich facets are in contrast. • The reduction of surface carbon to methane for (1 1 1) and (11-1) facets is more facile than other facets. In heterogeneous catalysis, the interaction between adsorbates and substrate surface plays an important role on surface structure evolution and even the reaction mechanism. Herein, unified DFT calculation and ab initio atomistic thermodynamics were adopted to explore the interaction between hydrogen and multiple Fe 5 C 2 surfaces. The computation indicates that the dissociation of hydrogen molecule is both thermodynamically and kinetically favorable on Fe 5 C 2 surfaces. The adsorption energy of hydrogen atoms is related to the summed H bond valance (SBV H), a higher SBV H corresponding to a more stable adsorption strength. Based on calculated surface free energy with different hydrogen coverage, the equilibrium crystalline morphology evolution of Fe 5 C 2 under dynamic conditions was constructed with Wulff theorem. C-rich facets expose more area in Wulff construction with decreasing hydrogen chemical potential. The generation of carbon vacancy through reducing to methane has also been investigated, and the reduction of (1 1 1) and (11-1) facets is more facile than other facets. We anticipate this work could complement some knowledge to help understanding the surface structure and performance of iron carbide catalysts under experimental conditions. [ABSTRACT FROM AUTHOR]

Silver decorated titania nanorod array (Ag/TiO2 NRA) and nanopore array (Ag/TiO2 NPA) had been designed as surface-enhanced Raman scattering (SERS) active substrate for a sensitive detection application. TiO2 NRA grown on glass slide was fabricated through hydrothermal synthesis process. TiO2 NPA grown on the titanium sheet was fabricated by a two-stepped anodization process. Ag/TiO2 NRA and Ag/TiO2 NPA were formed by depositing silver nanoparticles on TiO2 nanoarray through an electroless deposition process. Ag/TiO2 NRA had smaller silver interparticle gaps and more hot-spots than Ag/TiO2 NPA, exhibiting a higher SERS activity. The analytical enhancement factor was accordingly increased from 1.8 x 105 for Ag/TiO2 NPA up to 7.8 x 105 for Ag/TiO2 NRA. Ag/TiO2 NRA substrate achieved a very low detection limit of 5 x 10-12 M 4-mercaptobenzoic acid as a probe molecule, showing a sensitive SERS detection performance. Ag/TiO2 NRA also conducted photocatalysis decomposition of these adsorbed organic molecules to recover a clean surface under UV irradiation, exhibiting a self-cleaning activity. Such an Ag/TiO2 nanoarray with well-controlled size and shape could be suitably applies as a self-cleaning SERS substrate, showing high reproducibility and cycleability in recycling SERS detection application. [ABSTRACT FROM AUTHOR]

[Display omitted] • Main features of GDOES, XPS and ToF-SIMS depth profiling of the thin amine polymer film are compared. • GDOES depth profiling in Ar/O 2 mixture increases etching rate and depth resolution for amine polymer film compared to pure Ar gas. • Etching of polymer surface by glow discharge of Ar/O 2 mixture is based on the synergy of ion sputtering and reactive chemical etching. • GDOES depth profiling is suitable for fast analyses of polymer layers up to a few μm in thickness. Thin polymer films were deposited on polished stainless-steel samples by PECVD from a cyclopropylamine precursor and characterized by X-ray photoelectron spectroscopy, secondary-ion mass spectrometry and glow-discharge optical emission spectroscopy (GDOES) depth profiling. These depth profiles exhibited reasonable agreement. The GDOES involved the erosion of the polymer films in plasma sustained by an asymmetric RF capacitively coupled discharge using both Ar and Ar-O 2 gases. The application of pure Ar caused unwanted effects, such as the broadening of the polymer-film/substrate interface, which were suppressed when using the mixture with oxygen. Another benefit of oxygen was a significant increase in the etching rate by a factor of about 15 as compared to pure argon. The mechanisms involved in the depth profiling using the mixture of gases were elaborated in some detail, taking into account plasma parameters typical for an asymmetric, capacitively coupled RF discharge in a small volume. The main benefit of using the Ar/O 2 GDOES profiling with respect to XPS and SIMS depth profiling is the increased sputtering rate for polymer films. Comparing the GDOES depth profiling with the Ar/O 2 mixture with profiling in pure Ar, the benefits are a higher sputtering rate and better depth resolution at the polymer/substrate interface. [ABSTRACT FROM AUTHOR]

The CO 2 formation mechanism on Fe x C y and its structure–reactivity relationship during sintering process were systemically elucidated using the ReaxFF. [Display omitted] • Investigate the structure-activity relationship of different Fe-based nanoparticles in the sintering process. • Formation of low-coordination-number atoms may be the real reason for promoted TOF of the sintering structures. • The increased amplitude of surface area of sintered Fe x C y varies with its content of carbon. • The main CO 2 formation varies with the Fe x C y : Eley-Rideal VS. Langmuir-Hinshelwood mechanism. The sintering of nanostructured catalysts poses a grand challenge in understanding the complex mechanism in the experimental phenomena, as well as the structure-activity relationship. Here, we systematically investigate the structure-activity relationship of sintered Fe-based catalysts, including Fe 2 C, Fe 5 C 2 , Fe 3 C and pure Fe, in the CO activation by reactive molecular dynamics simulations. The results show that the sintering structures can promote the turn-over frequency of Fe 3 C compared with its un-sintered near-size structures, which might be attributed to the formation of low-coordination-number atoms. The change of surface area shows a similar trend for Fe x C y and pure Fe, and its increased magnitude varies with the content of carbon in the Fe x C y bulk. For size effect, the Fe 2 C displays the largest turn-over frequency for the 4.34 nm particle. The CO 2 formation mechanism has also been compared for different Fe x C y , which may provide critical theoretical insights for industrial reduction of CO 2 emission. [ABSTRACT FROM AUTHOR]

• On (2 1 0) surface, the hydrogen dissociation is spontaneous. • The chemical bonding analysis is employed to elucidate the interaction between adsorbate and substrate. • At high coverage, the hydrogen adsorption configuration is surface-dependent. • On (2 1 0) surface, the surface sulfur atoms are easily to be removed by hydrogen. Elucidating the interactions between hydrogen and catalysts under complex realistic conditions is of great importance in rationally modulating the catalytic performance of hydrogenation processes. Herein, we have investigated the interaction between hydrogen and four typical surfaces, (1 0 0), (2 1 0), (2 1 1), and (3 1 1) of pyrite FeS 2 through density functional theory calculations. On (2 1 0) surface, the hydrogen dissociative adsorption on unsaturated-coordination sulfur atoms is favorable both in thermodynamics and kinetics. The hydrogen activation barrier is 0.83 eV with slight exothermic of 0.12 eV on (3 1 1). While on (1 0 0) and (2 1 1) surface, the hydrogen dissociation is unfavorable due to the high activation barriers and remarkable positive reaction energies. For high adsorption coverage, the pure molecule adsorption mode is favorable on (1 0 0) facet, opposed to the other surfaces which have temperature and pressure dependence. The saturated coverage sequence is (1 0 0) > (2 1 0) > (2 1 1) > (3 1 1) for a wide range of temperature and pressure. The remove of sulfur atoms most likely occurs on (2 1 0) surface. Our atomistic insights might be useful in engineering hydrogen-involved processes catalyzed by iron sulfide. [ABSTRACT FROM AUTHOR]

• The boron chemical potential were calculated as a function of temperature, pressure and gas composition. • The bulk and surface stabilities of six iron borides are determined by the boron chemical potential. • The evolution of surface structure and morphology under dynamic conditions were predicted. • CO adsorption is weakened by surface doping of boron atom due to its electronegativity. Surface feature and its variation along with complex atmosphere are of fundamental significance to understanding the functionality of applied materials especially in heterogeneous catalysis and corrosion prevention. Here we performed a unified theoretical study on the surface structure and morphology of iron borides and their evolution under dynamic gaseous conditions by combination of density functional theory, ab initio atomic thermodynamics and Wulff construction. In particular, thermodynamic stability of iron borides and corresponding surfaces varied from the boron chemical potential (Δ μ B ) of certain atmosphere, which increases with decreasing pressure and increasing temperature and concentration of boron source. The stability of boron-rich surfaces has been improved with increasing Δ μ B , while all the Fe-rich facets of iron borides are favorable at low Δ μ B condition. Accordingly, the crystallite morphology of iron borides undergoes significant evolution upon dynamic condition. Finally, the surface properties of iron borides are carefully tested by CO adsorption which indicated the activation ability of CO is closely connected with boron triggered surface charge transfer between Fe and CO. This work was expected not only to help understand the surface structure and morphology of iron borides under realistic condition, but also provides fundamental insights into rational design of corrosion resistant and catalytic materials. [ABSTRACT FROM AUTHOR]