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Haijun Jiao - One of the best experts on this subject based on the ideXlab platform.
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coverage dependent water Dissociative Adsorption properties on nickel surfaces
Journal of Physical Chemistry C, 2020Co-Authors: Ling Zhu, Chunli Liu, Xiaodong Wen, Haijun JiaoAbstract:Periodic density functional theory calculations were employed to study the mechanisms of H2O Dissociative Adsorption on the Ni(211) surface at different coverages. Due to stronger H-bonding, H2O cl...
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coverage dependent structure and energy of water Dissociative Adsorption on clean and o pre covered ni 100 and ni 110
Catalysis Science & Technology, 2019Co-Authors: Ling Zhu, Chunli Liu, Xiaodong Wen, Haijun JiaoAbstract:Due to its importance in energy related catalytic reactions, H2O Dissociative Adsorption on clean and O pre-covered Ni(100) and Ni(110) surfaces has been computed systematically on the basis of periodic density functional theory and ab initio atomistic thermodynamics. On clean surfaces, H2O Adsorption prefers the top site at the lowest coverage and forms clusters stabilized by more dominant H-bonding interaction with the increase in coverage; H2O dissociation [H2O = OH + H] has a lower barrier than OH dissociation [OH + H = O + 2H], and both steps are exothermic on Ni(100) and Ni(111), while on Ni(110) the first step is exothermic and the second step is endothermic, indicating that surface OH should represent the most preferred species. Co-adsorbed H2O can lower the barrier of H2O dissociation, in agreement with the experiment. On O pre-covered surfaces, co-Adsorption of O and H2O prefers the remote configuration without H-bonding on Ni(100), the adjacent configuration with H-bonding on Ni(111) and barrier-less dissociation on Ni(110). Using H2O as an oxidant, surface OH saturation coverage on Ni(111), Ni(100) and Ni(110) is 0.625, 0.83 and higher than 1 ML, respectively, and surface O saturation coverage on Ni(111), Ni(100) and Ni(110) is 0.25, 0.42 and 0 ML, respectively. The desorption temperature of molecularly adsorbed H2O clusters and H2O from OH disproportionation [2OH = O + H2O(g)] agrees very well with the experimental values. The desorption temperature of H2 from H2O dissociation [OH + H = OH + 0.5H2(g) and O + 2H = O + H2(g)] agrees very well with the experimental value on Ni(100), but is lower than that on Ni(110). The computed desorption order of H2 and H2O from OH disproportionation, i.e., H2O prior to H2 on Ni(100) and H2 prior to H2O on Ni(110), agrees with the experimental finding. These systematic results show mechanistic insight into H2O Dissociative Adsorption on Ni surfaces and provide the basis for investigating water-involving reactions catalyzed by nickel.
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nitridation of the metallic mo2c 001 surface from nh3 Dissociative Adsorption a dft study
Surface Science, 2019Co-Authors: Fan Wang, Haijun JiaoAbstract:Abstract Adsorption and sequential decomposition of ammonia on the metallic Mo 2 C(001) surface have been systematically computed using periodic density functional theory under the consideration of van der Waals dispersion correction (PBE-D3). It is found that NH 3 Adsorption prefers the top sites from low to saturation coverage. For the Adsorption of surface NH 2 , bridge and hollow sites are possible at low coverage and only bridge sites are preferred at high coverage up to saturation. The Adsorption of surface NH and N prefers the hollow sites. Sequential decomposition of NH 3 into surface NH 2 , NH and N has low barrier and is highly exothermic. On the basis of surface Mo atoms, the saturation coverage of surface NH 3 , NH 2 , NH and N by using NH 3 as nitridation agent is 0.75, 1.0, 1.0 and 0.5 monolayer, respectively. These results provide the basis for the study of surface properties and catalytic reaction of nitrided Mo 2 C surfaces. The Dissociative Adsorption of ammonia among others metals and molybdenum nitrides has been categorized and compared.
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molecular or Dissociative Adsorption of water on clean and oxygen pre covered ni 111 surfaces
Catalysis Science & Technology, 2019Co-Authors: Ling Zhu, Chunli Liu, Xiaodong Wen, Haijun JiaoAbstract:Water Adsorption and dissociation on clean and oxygen pre-covered Ni(111) surfaces have been computed systematically by using density functional theory and ab initio atomistic thermodynamics. The Adsorption of H, O and OH prefers 3-fold faced centered cubic hollow sites, and that of H2O prefers the top site. For (H2O)n aggregation, direct O–Ni interaction and H-bonding synergistically determine the Adsorption energy, which is structure insensitive for large adsorbed clusters. At low coverage (θ ≤ 0.25 ML), OH adsorbs perpendicularly and prefers remote distribution without H-bonding, and the OH saturation coverage should be 0.625 ML on the basis of H2O Dissociative Adsorption. The Adsorption configuration for 4O (0.25 ML) prefers a p(2 × 2) structure, in agreement with the experiment, and the O saturation coverage should be 0.25 ML based on H2O Dissociative Adsorption. On the 0.25 ML O pre-covered Ni(111), H2O greatly prefers molecular Adsorption [4O + 4H2O(s)] over Dissociative Adsorption [8OH] thermodynamically, and this is in agreement with the photoelectron spectroscopy results and in disagreement with previously and recently proposed results from single crystal Adsorption calorimetry of D2O Adsorption. It is noted that the computed bond energy and formation enthalpy of the supposed surface hydroxyls on the basis of the molecular adsorbed state [4O + 4H2O(s)] are much closer to the experimentally estimated results than those computed on the basis of the Dissociatively adsorbed state [8OH]. Furthermore, the computed H2O desorption temperature on the basis of the molecular adsorbed state [4O + 4H2O(s)] is in excellent agreement with experimental results (284 vs. 275–300 K), while that from the Dissociatively adsorbed state [8OH] differs strongly (197 K). All these support H2O molecular Adsorption instead of Dissociative Adsorption, and this needs further experimental investigations and confirmations. The vibrational frequencies of 4O, 4O + 4H2O and 8OH Adsorption configurations have been computed to aid experimental studies.
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coverage dependent water Dissociative Adsorption on the clean and o precovered fe 111 surfaces
Journal of Physical Chemistry C, 2015Co-Authors: Shaoli Liu, Xiaodong Wen, Haijun Jiao, Xinxin Tian, Tao Wang, Jianguo WangAbstract:Water Dissociative Adsorption on the clean and O-precovered Fe(111) surfaces at different coverage have been studied using the density functional theory method (GGA-PBE) and ab initio atomistic thermodynamics. On the clean p(3 × 3) Fe(111) surface, surface H, O, OH, and H2O species can migrate easily. Considering Adsorption and H-bonding, the adsorbed H2O molecules can be dispersed or aggregated in close energies at low coverage, while in different aggregations at high coverage, indicating that the adsorbed H2O molecules might not have defined structures, as observed experimentally. On the O-precovered surface (nO = 1–8), the first dissociation step, nO + H2O = (n – 1)O + 2OH, has a very low barrier and is reversible; and the barriers of the sequential OH dissociation steps, (n – 1)O + 2OH = nO + H + OH and nO + H + OH = (n + 1)O + 2H, are close (0.9–1.2 eV). All of these barriers are coverage independent. For OH and H Adsorption at 1/3 ML coverage, surface OH forms a trimer (OH)3 unit, and surface O form...
Charles T Campbell - One of the best experts on this subject based on the ideXlab platform.
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formic acid Dissociative Adsorption on nio 111 energetics and structure of adsorbed formate
Journal of Physical Chemistry C, 2017Co-Authors: Wei Zhao, Jens K. Nørskov, Michal Bajdich, Andrew D Doyle, Sawyer E Morgan, Charles T CampbellAbstract:The Dissociative Adsorption of carboxylic acids on oxide surfaces is important for understanding adsorbed carboxylates, which are important as intermediates in catalytic reactions, for the organo-functionalization of oxide surfaces, and in many other aspects of oxide surface chemistry. We present here the first direct experimental measurement of the heat of Dissociative Adsorption of any carboxylic acid on any single-crystal oxide surface. The enthalpy of the Dissociative Adsorption of formic acid, the simplest carboxylic acid, to produce adsorbed formate and hydrogen (as a surface hydroxyl) on a (2 × 2)-NiO(111) surface is measured by single crystal Adsorption calorimetry. The differential heat of Adsorption decreases with formic acid coverage from 202 to 99 kJ/mol at saturation (0.25 ML). The structure of the adsorbed products is clarified by density functional theory (DFT) calculations, which provide energies in reasonable agreement with the calorimetry. These calculations show that formic acid readily...
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water Dissociative Adsorption on nio 111 energetics and structure of the hydroxylated surface
ACS Catalysis, 2016Co-Authors: Wei Zhao, Jens K. Nørskov, Michal Bajdich, Spencer J Carey, Aleksandra Vojvodic, Charles T CampbellAbstract:The energetics of the reactions of water with metal oxide surfaces are of tremendous interest for catalysis, electrocatalysis, and geochemistry, yet the energy for the Dissociative Adsorption of water was only previously measured on one well-defined oxide surface, iron oxide. In the present paper, the enthalpy of the Dissociative Adsorption of water is measured on NiO(111)-2 × 2 at 300 K using single-crystal Adsorption calorimetry. The differential heat of Dissociative Adsorption decreases with coverage from 170 to 117 kJ/mol in the first 0.25 ML of coverage. Water adsorbs molecularly on top of that, with a heat of ∼92 kJ/mol. Density functional theory (DFT) calculations reproduce the measured energies well (all within 17 kJ/mol) and provide insight into the atomic-level structure of the surfaces studied experimentally. They show that the oxygen-terminated O-octo(2 × 2) structure is the most stable NiO(111)-2 × 2 termination and gives reaction energies with water that are more consistent with the calorime...
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energetics of adsorbed ch2 and ch on pt 111 by calorimetry the Dissociative Adsorption of diiodomethane
Journal of Physical Chemistry C, 2014Co-Authors: Christopher A Wolcott, Trent L Silbaugh, Isabel Xiaoye Green, Ye Xu, Charles T CampbellAbstract:The enthalpies of molecular and Dissociative Adsorption of CH2I2 on Pt(111) at 100–210 K were studied using single-crystal Adsorption calorimetry and density functional theory (DFT). Gaseous CH2I2 was found to adsorb on the Pt(111) surface at 100 K to form CH2,ad + 2Iad, with a calorimetric heat of Adsorption that decreases with coverage as 222–480θ kJ/mol for θ < 1/8, where θ is the coverage in monolayers (ML), defined as the number of Dissociatively adsorbed CH2I2 molecules per Pt(111) surface atom. These coadsorbed iodine atoms greatly destabilize the methylene species even at the lowest coverage, which we attribute to their inability to diffuse away from the near-neighbor sites where they are initially produced on the short time scale of the heat measurement. A mixture of Dissociative Adsorption fragments of methylene and methylidyne were detected at elevated temperatures between 125 and 190 K. At 210 K, CH2I2 Adsorption produced CHad, Had, and 2Iad, with the Iad now able to diffuse away to minimize r...
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energetics of formic acid conversion to adsorbed formates on pt 111 by transient calorimetry
Journal of the American Chemical Society, 2014Co-Authors: Trent L Silbaugh, Eric M Karp, Charles T CampbellAbstract:Carboxylates adsorbed on solid surfaces are important in many technological applications, ranging from heterogeneous catalysis and surface organo-functionalization to medical implants. We report here the first experimentally determined enthalpy of formation of any surface bound carboxylate on any surface, formate on Pt(111). This was accomplished by studying the Dissociative Adsorption of formic acid on oxygen-presaturated (O-sat) Pt(111) to make adsorbed monodentate and bidentate formates using single-crystal Adsorption calorimetry. The integral heat of molecular Adsorption of formic acid on clean Pt(111) at 100 K is 62.5 kJ/mol at 0.25 monolayer (ML). On O-sat Pt(111), the integral heat of the Dissociative Adsorption of formic acid to make monodentate formate (HCOOmon,ad) plus the water–hydroxyl complex ((H2O–OH)ad) was found to be 76 kJ/mol at 3/8 ML and 100–150 K. Similarly, its integral heat of Dissociative Adsorption to make bidentate formate (HCOObi,ad) plus (H2O–OH)ad was 106 kJ/mol at 3/8 ML and ...
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the Dissociative Adsorption of h2 and d2 on cu 110 activation barriers and dynamics
Surface Science, 1991Co-Authors: J M Campbell, Charles T CampbellAbstract:Abstract A true Arrhenius activation energy for the Dissociative Adsorption of H 2 on Cu(110) was measured using a Boltzmann distribution of H 2 gas at the surface temperature and found to be 14.3 ± 1.4 kcal/mol with a pre-exponential factor of 10 0.03±0.16 per H 2 collision with the surface. The temperature of the H 2 gas impinging on the heated Cu(110) surface was brought to the surface temperature ( ∼ 623 K) from the cold wall temperature ( ∼ 300 K) by increasing the total pressure in the reaction vessel with inert N 2 . This increases the translational and internal energy of H 2 by collisional energy transfer near the surface. The rate of Dissociative H 2 Adsorption was found to increase strongly with the addition of N 2 up to ∼ 2 Torr, but to increase slowly above that, consistent with a “direct” mechanism for Dissociative Adsorption where the H 2 translational energy is most effective in scaling the activation barrier. Gas-phase collisional energy transfer was computer-simulated using known energy transfer rates to determine the average translational and internal energies of H 2 impinging on the copper surface as a function of N 2 pressure. The translational, rotational, and vibrational temperatures approach the surface temperature at widely different N 2 pressures, allowing assessment of the relative effectiveness of these degrees of freedom in assisting H 2 Adsorption. Comparison of the activation energy with the desorption energy of adsorbed hydrogen indicates that the Adsorption of hydrogen is nearly thermoneutral. Similar results are also reported here for D 2 Adsorption, where no significant differences between D 2 and H 2 could be seen.
Matthias Scheffler - One of the best experts on this subject based on the ideXlab platform.
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effect of the cluster size in modeling the h2 desorption and Dissociative Adsorption on si 001
Journal of Chemical Physics, 1999Co-Authors: Evgeni S Penev, Peter Kratzer, Matthias SchefflerAbstract:Three different clusters, Si9H12, Si15H16, and Si21H20, are used in density-functional theory calculations in conjunction with ab initio pseudopotentials to study how the energetics of H2 Dissociative Adsorption on and associative desorption from Si(001) depends on the cluster size. The results are compared to five-layer slab calculations using the same pseudopotentials and high quality plane-wave basis set. Several exchange-correlation functionals are employed. Our analysis suggests that the smaller clusters generally overestimate the activation barriers and reaction energy. The Si21H20 cluster, however, is found to predict reaction energetics, with Eades=56±3kcal/mol (2.4±0.1eV), reasonably close (though still different) to that obtained from the slab calculations. Differences in the calculated activation energies are discussed in relation to the efficiency of clusters to describe the properties of the clean Si(001)-2×1 surface.
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ab initio quantum and molecular dynamics of the Dissociative Adsorption of hydrogen on pd 100
Physical Review B, 1998Co-Authors: Axel Gross, Matthias SchefflerAbstract:The Dissociative Adsorption of hydrogen on Pd(100) has been studied by ab initio quantum dynamics and ab initio molecular-dynamics calculations. Treating all hydrogen degrees of freedom as dynamical coordinates implies a high dimensionality and requires statistical averages over thousands of trajectories. An efficient and accurate treatment of such extensive statistics is achieved in a three-step approach: In a first step we evaluate the ab initio potential-energy surface (PES) for a number of appropriate points in configuration space. Then (as step 2) we determine an analytical representation that serves as an interpolation between the actually calculated points. In an independent third step dynamical calculations are performed on the analytical representation of the PES. Thus the dissociation dynamics is investigated without any crucial assumption except for the Born-Oppenheimer approximation which is anyhow employed when density-functional-theory calculations are performed. The ab initio molecular dynamics is compared to detailed quantum-dynamical calculations on exactly the same ab initio PES. The occurence of quantum oscillations in the sticking probability as a function of kinetic energy is addressed. They turn out to be very sensitive to the symmetry of the initial conditions. At low kinetic energies sticking is dominated by the steering effect, which is illustrated using classical trajectories. The steering effect depends on the kinetic energy, but not on the mass of the molecules, as long as no energy transfer to the substrate atoms is considered. The comparison between quantum and classical calculations of the sticking probability shows the importance of zero-point effects in the hydrogen dynamics. The dependence of the sticking probability on the angle of incidence is analyzed; it is found to be in good agreement with experimental data. The results show that the determination of the potential-energy surface combined with high-dimensional dynamical calculations, in which all relevant degrees of freedom are taken into account, leads to a detailed understanding of the dissociation dynamics of hydrogen at a transition metal surface.
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steering and ro vibrational effects in the Dissociative Adsorption and associative desorption of h_2 pd 100
arXiv: Condensed Matter, 1997Co-Authors: Axel Gross, Matthias SchefflerAbstract:The interaction of hydrogen with many transition metal surfaces is characterized by a coexistence of activated with non-activated paths to Adsorption with a broad distribution of barrier heights. By performing six-dimensional quantum dynamical calculations using a potential energy surface derived from ab initio calculations for the system H_2/Pd(100) we show that these features of the potential energy surface lead to strong steering effects in the Dissociative Adsorption and associative desorption dynamics. In particular, we focus on the coupling of the translational, rotational and vibrational degrees of freedom of the hydrogen molecule in the reaction dynamics.
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steering and ro vibrational effects on Dissociative Adsorption and associative desorption of h2pd 100
Progress in Surface Science, 1996Co-Authors: Axel Gross, Matthias SchefflerAbstract:Abstract The interaction of hydrogen with many transition metal surfaces is characterized by a coexistence of activated with non-activated paths to Adsorption with a broad distribution of barrier heights. By performing six-dimensional quantum dynamical calculations using a potential energy surface derived from ab initio calculations for the system H 2 Pd (100) we show that these features of the potential energy surface lead to strong steering effects in the Dissociative Adsorption and associative desorption dynamics. In particular, we focus on the coupling of the translational, rotational and vibrational degrees of freedom of the hydrogen molecule in the reaction dynamics.
Jens K. Nørskov - One of the best experts on this subject based on the ideXlab platform.
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formic acid Dissociative Adsorption on nio 111 energetics and structure of adsorbed formate
Journal of Physical Chemistry C, 2017Co-Authors: Wei Zhao, Jens K. Nørskov, Michal Bajdich, Andrew D Doyle, Sawyer E Morgan, Charles T CampbellAbstract:The Dissociative Adsorption of carboxylic acids on oxide surfaces is important for understanding adsorbed carboxylates, which are important as intermediates in catalytic reactions, for the organo-functionalization of oxide surfaces, and in many other aspects of oxide surface chemistry. We present here the first direct experimental measurement of the heat of Dissociative Adsorption of any carboxylic acid on any single-crystal oxide surface. The enthalpy of the Dissociative Adsorption of formic acid, the simplest carboxylic acid, to produce adsorbed formate and hydrogen (as a surface hydroxyl) on a (2 × 2)-NiO(111) surface is measured by single crystal Adsorption calorimetry. The differential heat of Adsorption decreases with formic acid coverage from 202 to 99 kJ/mol at saturation (0.25 ML). The structure of the adsorbed products is clarified by density functional theory (DFT) calculations, which provide energies in reasonable agreement with the calorimetry. These calculations show that formic acid readily...
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water Dissociative Adsorption on nio 111 energetics and structure of the hydroxylated surface
ACS Catalysis, 2016Co-Authors: Wei Zhao, Jens K. Nørskov, Michal Bajdich, Spencer J Carey, Aleksandra Vojvodic, Charles T CampbellAbstract:The energetics of the reactions of water with metal oxide surfaces are of tremendous interest for catalysis, electrocatalysis, and geochemistry, yet the energy for the Dissociative Adsorption of water was only previously measured on one well-defined oxide surface, iron oxide. In the present paper, the enthalpy of the Dissociative Adsorption of water is measured on NiO(111)-2 × 2 at 300 K using single-crystal Adsorption calorimetry. The differential heat of Dissociative Adsorption decreases with coverage from 170 to 117 kJ/mol in the first 0.25 ML of coverage. Water adsorbs molecularly on top of that, with a heat of ∼92 kJ/mol. Density functional theory (DFT) calculations reproduce the measured energies well (all within 17 kJ/mol) and provide insight into the atomic-level structure of the surfaces studied experimentally. They show that the oxygen-terminated O-octo(2 × 2) structure is the most stable NiO(111)-2 × 2 termination and gives reaction energies with water that are more consistent with the calorime...
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the reaction rate for Dissociative Adsorption of n2 on stepped ru 0001 six dimensional quantum calculations
Journal of Chemical Physics, 2005Co-Authors: Rob Van Harrevelt, Jens K. Nørskov, Karoliina Honkala, Uwe MantheAbstract:Quantum-mechanical calculations of the reaction rate for Dissociative Adsorption of N2 on stepped Ru(0001) are presented. Converged six-dimensional quantum calculations for this heavy-atom reaction have been performed using the multiconfiguration time-dependent Hartree method. A potential-energy surface for the transition-state region is constructed from density-functional theory calculations using Shepard interpolation. The quantum results are in very good agreement with the results of the harmonic transition-state theory. In contrast to the findings of previous model calculations on similar systems, the tunneling effect is found to be small.
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modification of the surface electronic and chemical properties of pt 111 by subsurface 3d transition metals
Journal of Chemical Physics, 2004Co-Authors: John R Kitchin, Jens K. Nørskov, Mark A Barteau, Jingguang G ChenAbstract:The modification of the electronic and chemical properties of Pt(111) surfaces by subsurface 3d transition metals was studied using density-functional theory. In each case investigated, the Pt surface d-band was broadened and lowered in energy by interactions with the subsurface 3d metals, resulting in weaker Dissociative Adsorption energies of hydrogen and oxygen on these surfaces. The magnitude of the decrease in Adsorption energy was largest for the early 3d transition metals and smallest for the late 3d transition metals. In some cases, Dissociative Adsorption was calculated to be endothermic. The surfaces investigated in this study had no lateral strain in them, demonstrating that strain is not a necessary factor in the modification of bimetallic surface properties. The implications of these findings are discussed in the context of catalyst design, particularly for fuel cell electrocatalysts.
Manos Mavrikakis - One of the best experts on this subject based on the ideXlab platform.
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how coverage influences thermodynamic and kinetic isotope effects for h2 d2 Dissociative Adsorption on transition metals
Catalysis Science & Technology, 2020Co-Authors: Benjamin W J Chen, Manos MavrikakisAbstract:Isotope effects greatly enhance our understanding of chemical reactions in heterogeneous catalysis. Despite their widespread use, there is limited understanding about how realistic reaction conditions, such as the coverage of surface adsorbates, affect them. Here, we study the influence of hydrogen (H) coverage on the thermodynamic and kinetic isotope effects of H2/D2 Dissociative Adsorption on the close-packed, open, and stepped surfaces of 12 transition metals: Ag, Au, Co, Cu, Fe, Ir, Ni, Re, Pd, Pt, Rh, and Ru, over a catalytically relevant temperature range. Through first-principles density functional theory calculations, we show that increasing coverage has two effects: i) it may change preferred Adsorption sites and transition state geometries, and ii) it increases the vibrational frequencies of adsorbed H due to the interactions between H atoms. Empirically, isotope effects decrease in absolute value with increasing coverage for most of our studied systems, indicating a relative shift in stability in favor of the D-substituted minima and transition states. This is likely due to the consistent influence of the latter factor, which affects all structures. Higher temperatures reduce the magnitude of these decreases. Our findings provide insights into the nanoscale mechanisms by which coverage influences isotope effects, which will affect how we interpret experimentally measured isotope effects. They also point towards new applications of isotope effects in catalysis, such as for quantifying adsorbate coverages as well as for elucidating Adsorption and active sites on the surfaces of catalysts.
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amplification of elementary surface reaction steps on transition metal surfaces using liquid crystals Dissociative Adsorption and dehydrogenation
Journal of the American Chemical Society, 2019Co-Authors: Tibor Szilvasi, Manos Mavrikakis, Kunlun Wang, Jake I Gold, Robert J Twieg, Nanqi Bao, Nicholas L AbbottAbstract:Elementary reaction steps, including Adsorption and dissociation, of a range of molecular adsorbates on transition metal surfaces have been elucidated in the context of chemical catalysis. Here we leverage this knowledge to design liquid crystals (LCs) supported on ultrathin polycrystalline gold films (predominant crystallographic face is (111)) that are triggered to undergo orientational transitions by Dissociative Adsorption and dehydrogenation reactions involving chlorine and carboxylic acids, respectively, thus amplifying these atomic-scale surface processes in situ into macroscopic optical signals. We use electronic structure calculations to predict that 4'-n-pentyl-4-biphenylcarbonitrile (5CB), a room temperature nematic LC, does not bind to Au(111) in an orientation that changes upon Dissociative Adsorption of molecular chlorine, a result validated by experiments. In contrast, 4-cyano-4-biphenylcarboxylic acid (CBCA) is calculated to bind strongly to Au(111) in a perpendicular orientation via dehydrogenation of the carboxylic acid group, which we confirmed using polarization-modulation infrared reflection-absorption spectroscopy. A maximum coverage of 0.07 monolayer of CBCA on the gold surface is sufficient to cause a perpendicular orientation of the LC. Dissociative Adsorption of Cl2 gas on the gold surface, resulting in 0.5 monolayer coverage of Cl, displaces CBCA from Au(111) and thus triggers a strikingly visible change in orientation of the LC. Infrared spectroscopy established the orientation of adsorbed CBCA to be parallel to the Cl covered surface, with the COOH plane perpendicular to the surface, as predicted by first-principles calculations. These results demonstrate the use of first-principles calculations and transition metal surfaces to design LCs that report in situ targeted atomic-scale surface processes.
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amplification of elementary surface reaction steps on transition metal surfaces using liquid crystals Dissociative Adsorption and dehydrogenation
Journal of the American Chemical Society, 2019Co-Authors: Huaizhe Yu, Manos Mavrikakis, Tibor Szilvasi, Kunlun Wang, Jake I Gold, Robert J Twieg, Nicholas L AbbottAbstract:Elementary reaction steps, including Adsorption and dissociation, of a range of molecular adsorbates on transition metal surfaces have been elucidated in the context of chemical catalysis. Here we leverage this knowledge to design liquid crystals (LCs) supported on ultrathin polycrystalline gold films (predominant crystallographic face is (111)) that are triggered to undergo orientational transitions by Dissociative Adsorption and dehydrogenation reactions involving chlorine and carboxylic acids, respectively, thus amplifying these atomic-scale surface processes in situ into macroscopic optical signals. We use electronic structure calculations to predict that 4′-n-pentyl-4-biphenylcarbonitrile (5CB), a room temperature nematic LC, does not bind to Au(111) in an orientation that changes upon Dissociative Adsorption of molecular chlorine, a result validated by experiments. In contrast, 4-cyano-4-biphenylcarboxylic acid (CBCA) is calculated to bind strongly to Au(111) in a perpendicular orientation via dehyd...
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density functional theory study of thermodynamic and kinetic isotope effects of h2 d2 Dissociative Adsorption on transition metals
Catalysis Science & Technology, 2018Co-Authors: Yunhai Bai, Benjamin W J Chen, Guowen Peng, Manos MavrikakisAbstract:We studied the thermodynamic isotope effects (TIEs) and kinetic isotope effects (KIEs) for H2/D2 Dissociative Adsorption using periodic, density functional theory (DFT)-based calculations. We examined the TIEs on the close-packed, open, and stepped surfaces, of twelve transition metals (Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Re, Ir, Pt, and Au), and the KIEs on the surfaces of three noble metals (Cu, Ag, and Au). Both TIEs and KIEs were evaluated at 1/9 ML coverage. We find distinct TIEs on different Adsorption sites, indicating that TIEs could be used in conjunction with binding energies to determine the dominant Adsorption sites for hydrogen. Additionally, we find that while H2 Dissociative Adsorption may traditionally be considered structure insensitive in terms of reaction rates, it can exhibit structure sensitivity in terms of its KIEs. Complementarily to TIEs, KIEs might therefore be useful for identifying active sites for H2 Dissociative Adsorption on the three noble metal transition metal catalysts studied.