Bronsted Evans Polanyi Research Articles

Generalized Brønsted–Evans–Polanyi relationships and descriptors for O–H bond cleavage of organic molecules on transition metal surfaces

Periodic density functional theory (DFT) based calculations were used to explore the relationship between the activation energy corresponding to RO–H bond cleavage of organic compounds on catalytically active transition metal surfaces and other simpler quantities which can be used as descriptors. Taking data for methanol on various surfaces, several Brønsted–Evans–Polanyi (BEP)-like relationships linking the activation energy barrier to the reaction energy, the adsorption energy of the reaction products or to the adsorption energy of an oxygen atom were explored. The general validity of these relationships has been explored by considering cases not included in the database used to extract the BEP relationships. For the more promising BEP relationship, the database for methanol was combined with results corresponding to O–H bond breaking of ethanol, formic acid and water on a sufficiently broad number of transition metal surfaces. This extended database provided a more general and statistically meaningful general BEP type relationship connecting the activation energy for the O–H bond breakage of general RO–H compounds on catalytic transition metal systems to the adsorption energy of the reaction products. Finally, a protocol is presented that allows one to determine good candidates for bond breakage of general RO–H compounds on metallic and bimetallic surfaces limiting the explicit calculation of the activation energy barriers to a few, previously detected, interesting cases only.

Brønsted–Evans–Polanyi and Transition State Scaling Relations of Furan Derivatives on Pd(111) and Their Relation to Those of Small Molecules

Bronsted–Evans–Polanyi (BEP) and transition state scaling (TSS) linear free energy relations are extended to C–H, O–H, C–O and C–C bond breaking reactions occurring on the ring and the functional groups of furan (hydrofuran, dihydrofuran, trihydrofuran, and tetrahydrofuran) and furfural derivatives (e.g., furfural, furfuryl alcohol, methyl furan, etc.) on Pd(111). The relations perform statistically as well as those for small molecules reported previously. Hydrogenation/dehydrogenation reactions have smaller deviations compared to C–C and C–O bond breaking ones. This is in line with the degree of structural change during reaction and agrees with observations in previous works. We conclude that BEP relations developed for small molecules are not statistically different from those developed for furanics. A universal BEP relation is not statistically different from most of the BEP relations developed for furanics, with the exception of C–O, O–H and C–H scission reactions at the functional group, for which on...

Decomposition mechanism of methylamine to hydrogen cyanide on Pt(111): selectivity of the C–H, N–H and C–N bond scissions

Periodic density functional theory (DFT) calculations were performed to systematically investigate the decomposition mechanism of methylamine (CH3NH2) to hydrogen cyanide (HCN) on Pt(111). The geometries and energies for all species involved are analyzed, and the decomposition network is mapped out to elaborate the reaction mechanism. Our results show that the CH3NH2, methanimine (CH2NH) and HCN prefer to desorb, while the other species prefer to decompose; the decomposition pathway prefers the successive N–H bond scissions followed by the C–H bond scissions, that is, CH3NH2 → CH3NH → CH3N → CH2N → HCN. The electronic structure and energy barrier analysis are used to identify the initial competitive scissions of C–H, N–H and C–N bonds. The interaction between fragments and surface in the TS plays a decisive role in controlling the energy barrier of initial CH3NH2 decomposition on Pt(111). Finally, the Brønsted–Evans–Polanyi (BEP) relation identifies that the C–H and N–H bond scissions stay competitive, but the C–N bond scission is not facile to occur.

Understanding the Optimal Adsorption Energies for Catalyst Screening in Heterogeneous Catalysis

The fundamental understanding of the activity in heterogeneous catalysis has long been the major subject in chemistry. This paper shows the development of a two-step model to understand this activity. Using the theory of chemical potential kinetics with Bronsted–Evans–Polanyi relations, the general adsorption energy window is determined from volcano curves, using which the best catalysts can be searched. Significant insights into the reasons for catalytic activity are obtained.

Density functional theory study of propane steam reforming on Rh–Ni bimetallic surface: Sulfur tolerance and scaling/Brønsted–Evans–Polanyi relations

Enhanced sulfur tolerance on binary Rh–Ni metals is examined for the propane steam reforming process on close packed metal surfaces of Rh, Ni, Rh1Ni2, and Rh2Ni1 with and without co-adsorbed S atoms. Scaling and Brønsted–Evans–Polanyi (BEP) correlations are constructed from density functional theory (DFT) methods. The combined use of these methods produces significant errors among these similar metal surfaces; however, BEP relations applied within reaction types are reliable across Rh, Ni, and binary Rh–Ni surfaces with and without co-adsorbed S atoms. The potential energy surface of propane steam reforming, estimated using the BEP correlations, shows that the C–C cleavages of CHC*, CH3CC* and CH2C* along with the O addition to CH* are kinetically significant elementary steps. Three of these steps show only slight barrier increases with co-adsorbed S on the Rh2Ni1 surface, suggesting an energetic explanation for enhanced S tolerance. The average poisoning effect by the presence of co-adsorbed sulfur for bond breaking is minimized on binary Rh–Ni metals, suggesting a high sulfur resistance can be induced using a bimetallic formulation of Rh and Ni.

On the Structure Sensitivity of Direct NO Decomposition over Low-Index Transition Metal Facets

We present a study of the dissociative chemisorption of NO, O2, and N2 over close-packed, stepped, kinked, and open (fcc {111}, {211}, {311}, {532}, {100}, and {110}) transition metal facets using density functional theory (DFT). The offset of the Bronsted–Evans–Polanyi (BEP) relations suggest that the {111} surface is the least reactive, and that the {110} surface is the most reactive. This observation is verified by establishing volcano-relations based on mean-field microkinetic models for each facet, showing that the maximum rate over {110} is 4 orders of magnitude larger than the maximum {111} rate. The ordering of the maximum activity over the facets is: {110} > {100} ~ {532} > {311} ~ {211} > {111}, which is in general agreement with the offset in the BEP relations. We show that the top-point location and shape of the volcano relations are approximately independent of facet. This observation lends credibility to the approach of analyzing trends in catalytic reactivity over a single low-index facet, and assuming the experimentally observed activity trends are qualitatively well-described by such a single-facet analysis. Our study suggests that a key element for generally obtaining quantitative agreement between theory and experiments is for the simulations to address in detail the propensities of the various types of active sites. Finally, we show that the ordering of NO decomposition rates among metals and facets is essentially unaltered when using BEP- and scaling relations in the microkinetics instead of explicit DFT calculations for each elementary reaction step, and that using a “universal” BEP relation introduces no significant additional qualitative error in trend prediction.

Predicting CH4 Dissociation Kinetics on Metals: Trends, Sticking Coefficients, H Tunneling, and Kinetic Isotope Effect

The rate constant (W) of catalytic dissociation of a methane molecule to adsorbed CH3 and H and its temperature dependence are studied in the framework of a tunneling model which considers the reaction as a result of quantum transitions between discrete vibrational energy levels of an initial C–H bond in methane and energy continuum of the dissociated final state while the system reaches the transition state along other classical degrees of freedom. This step is assumed to be the rate determining one in many reactions of commercial significance like steam and dry reforming of methane. This approach has previously been successfully applied to other catalytic reactions of H atom transfer. Numerical calculations of the kinetic characteristics for the reaction proceeding over surfaces of Ni(111), Pt(111), Cu(111), Pd(111), Ru(001), and Ir(111) are interpreted in terms of the Brønsted–Evans–Polanyi (BEP) relationship. The good correlation and the theory show that the main discriminating parameter which determines the trend within a set of metals is the total adsorption energy of a methyl fragment and an H atom. The BEP relationship is used for prediction of the rate constants of the dissociation on rhodium, silver, and gold (111) surfaces and for predicting the activation energy on bimetallic surfaces. Sticking coefficients are estimated using the W values and adsorption energy of the methane molecule; the latter is approximately assumed to be the same for all considered surfaces. These estimations are compared with the experimental sticking coefficients for several metals showing quantitative agreement. Hydrogen kinetic isotope effects (KIEs) and their temperature dependencies are calculated for the dissociation on nickel and ruthenium surfaces, and the KIE estimates at fixed temperatures of iridium and rhodium are compared with the corresponding experimental data. Results of this comparison justify the application of the model for the description of the catalytic dissociation of the C–H bond.

A Systematic Investigation of p-Nitrophenol Reduction by Bimetallic Dendrimer Encapsulated Nanoparticles

We demonstrate that the reduction of p-nitrophenol to p-aminophenol by NaBH4 is catalyzed by both monometallic and bimetallic nanoparticles (NPs). We also demonstrate a straightforward and precise method for the synthesis of bimetallic nanoparticles using poly(amido)amine dendrimers. The resulting dendrimer encapsulated nanoparticles (DENs) are monodisperse, and the size distribution does not vary with different elemental combinations. Random alloys of Pt/Cu, Pd/Cu, Pd/Au, Pt/Au, and Au/Cu DENs were synthesized and evaluated as catalysts for p-nitrophenol reduction. These combinations are chosen in order to selectively tune the binding energy of the p-nitrophenol adsorbate to the nanoparticle surface. Following the Brønsted–Evans–Polanyi (BEP) relation, we show that the binding energy can reasonably predict the reaction rates of p-nitrophenol reduction. We demonstrate that the measured reaction rate constants of the bimetallic DENs is not always a simple average of the properties of the constituent metals. In particular, DENs containing metals with similar lattice constants produce a binding energy close to the average of the two constituents, whereas DENs containing metals with a lattice mismatch show a bimodal distribution of binding energies. Overall, in this work we present a uniform method for synthesizing pure and bimetallic DENs and demonstrate that their catalytic properties are dependent on the adsorbate’s binding energy.

A Tunnel Model for Activated Hydrogen Dissociation on Metal Surfaces

Activated dissociative adsorption of a hydrogen molecule on metal surfaces is studied in the framework of the precursor mediated dissociation (PMD) mechanism according to which the dissociation proceeds through a molecular-adsorbed state (precursor) which then dissociates to H atoms. The PMD activation energies and rate constants are calculated by considering quantum transitions from various vibration levels of initial state into a continuous manifold of energies of the final dissociated state. The geometric parameters required are taken from the literature for a nickel surface while on other metals the same geometry is assumed to hold but the energies differ. This approach is applied to gain an insight into specific details of the reaction mechanism. The Bronsted–Evans–Polanyi relationship coefficients are obtained and used for prediction of the catalytic reactivity of a wide range of (111) metals and alloys. Hydrogen kinetic isotope effect (KIE) of the reaction on the palladium surface and its temperatu...

Brønsted–Evans–Polanyi Relationship for Transition Metal Carbide and Transition Metal Oxide Surfaces

The splitting of O2 on transition metal, transition metal carbide, and transition metal oxide surfaces is analyzed in the framework of Bronsted–Evans–Polanyi (BEP) relationships. It is shown that these hold for all three types of substrates, thus giving support to the idea of universality behind these useful relationships. Moreover, comparison of the BEP relationships for the three substrates suggests a significantly higher catalytic activity on metal carbides and rutile metal oxides.

A density functional theory analysis of trends in glycerol decomposition on close-packed transition metal surfaces

We describe an accelerated density functional theory (DFT)-based computational strategy to determine trends in the decomposition of glycerol via elementary dehydrogenation, C-C, and C-O bond scission reactions on close-packed transition metal surfaces. Beginning with periodic DFT calculations on Pt(111), the thermochemistry of glycerol dehydrogenation on Pd(111), Rh(111), Cu(111) and Ni(111) is determined using a parameter-free, bond order-based scaling relationship. By combining the results with Brønsted-Evans-Polanyi (BEP) relationships to estimate elementary reaction barriers, free energy diagrams are developed on the respective metal surfaces, and trends concerning the relative selectivity and activity for C-C and C-O bond scission in glycerol on the various metals are obtained. The results are consistent with available theoretical and experimental literature and demonstrate that scaling relationships are capable of providing powerful insights into the catalytic chemistry of complex biomolecules.

Ethanoldecomposition on a Pd(110) surface: a density functional theory investigation

Ethanol decomposition on Pd(110) is comprehensively investigated using self-consistent periodic density functional theory. Geometries and energies for all the intermediates involved are analyzed, and the decomposition network is mapped out to illustrate the reaction mechanism. On Pd(110), the most stable adsorption of the involved species tends to follow the gas-phase bond order rules, wherein C is tetravalent and O is divalent with the missing H atoms replaced by metal atoms. The most likely decomposition pathway of ethanol on Pd(110) is CH(3)CH(2)OH → CH(3)CH(2)O → CH(3)CHO → CH(3)CO → CH(3) + CO → CO + H + CH(4) + C, in which the initial dehydrogenation is the rate-limited step. No C-O scission pathway is identified. Comparing with ethanol decomposition on Pd(111) [Langmuir, 2010, 26, 1879-1888], Pd(110) characterizes relatively high activity and different selectivity. Two crucial factors controlling the variations of reactivity and selectivity from Pd(111) to Pd(110), i.e., the local electronic effect of the metals and the geometrical effect of the relevant transition states, are identified. Four distinct Brønsted-Evans-Polanyi (BEP) relations are identified for the three types of bond scission (C-H, C-O, and C-C) if we consider Pd(111) and Pd(110) as a whole, one for C-H bond scission, one for C-O bond scission, and two for C-C bond scission.

Error estimates in semi-empirical estimation methods of surface reactions

In this paper, we examine the theoretical and numerical error properties of three semi-empirical methods when used separately and in conjunction with each other using oxygenated hydrocarbons as sample species. These methods are group additivity (GA), the linear scaling relations (LSRs), and the Brønsted–Evans–Polanyi (BEP) correlations. GA estimated heat of formation has nearly zero mean error for all species. GA heats of reaction have no systematic error only when GA is used with C2 or larger species, and DFT is used for all smaller species. Aside from a constant offset, LSR-estimated binding energies and heats of reaction show adequate agreement with the corresponding DFT energies. BEP-estimated activation energies are shown to have systematic errors when the input heats of reaction have systematic errors. Each method produces estimates whose errors are normally distributed with a nonzero mean and which are uncorrelated. Combinations of techniques also possess normally distributed errors.

DFT Study of the Water–Gas Shift Reaction and Coke Formation on Ni(111) and Ni(211) Surfaces

We report for the first time results of a systematic density functional theory (DFT) study of the water-gas shift (WGS) reaction and coke formation pathways on Ni(111) and Ni(211) surfaces, consisting of 21 elementary-like steps and 12 surface species. Bronsted–Evans–Polanyi correlations are proposed for dehydrogenation and C–O bond breaking reactions on flat and stepped surfaces. The DFT results suggest that the flat surface is slightly more active for the WGS reaction, which occurs mainly via the carboxyl pathway with the CO* + OH* ⇌ COOH*+* as the rate determining step. On the stepped surface, beyond the carboxyl pathway, the DFT energetics indicates that a parallel route via formate and formyl intermediates is favored. Ni(111) has a much lower activity for C–O bond breaking, and thus, flat surfaces are less susceptible to deactivation by coke.

A Theoretical and Computational Analysis of Linear Free Energy Relations for the Estimation of Activation Energies

We present a theoretical and computational analysis to elucidate the relation of the Bronsted–Evans–Polanyi (BEP) and transition state scaling (TSS) correlations. We find that the TSS correlation is an approximation of the BEP correlation. The BEP correlation allows for the straightforward identification of homologous series via standard statistical tests and has better error properties than the TSS correlations. We find that the unit cell size used in the DFT calculations does not have a significant effect on the correlation parameters; however, the zero point energy correction does have a significant effect on the correlation parameters, especially for (de)hydrogenation reactions. We propose a method for using this information to estimate zero-point-energy-corrected activation energies without resorting to calculations of the zero point energy correction for every species. Finally, we find that BEP correlations derived for one parent molecule may be applicable to other molecules beyond the training set.

Density Functional Theory Study of Selectivity Considerations for C–C Versus C–O Bond Scission in Glycerol Decomposition on Pt(111)

Glycerol decomposition via a combination of dehydrogenation, C–C bond scission, and C–O bond scission reactions is examined on Pt(111) with periodic Density Functional Theory (DFT) calculations. Building upon a previous study focused on C–C bond scission in glycerol, the current work presents a first analysis of the competition between C–O and C–C bond cleavage in this reaction network. The thermochemistry of various species produced from C–O bond breaking in glycerol dehydrogenation intermediates is estimated using an extension of a previously introduced empirical correlation scheme, with parameters fit to DFT calculations. Bronsted–Evans–Polanyi (BEP) relationships are then used to estimate the kinetics of C–O bond breaking. When combined with the previous results, the thermochemical and kinetic analyses imply that, while C–O bond scission may be competitive with C–C bond scission during the early stages of glycerol dehydrogenation, the overall rates are likely to be very low. Later in the dehydrogenation process, where rates will be much higher, transition states for C–C bond scission involving decarbonylation are much lower in energy than are the corresponding transition states for C–O bond breaking, implying that the selectivity for C–C scission will be high for glycerol decomposition on smooth platinum surfaces. It is anticipated that the correlation schemes described in this work will provide an efficient strategy for estimating thermochemical and kinetic energetics for a variety of elementary bond breaking processes on Pt(111) and may ultimately facilitate computational catalyst design for these and related catalytic processes.

Brønsted–Evans–Polanyi Relations for H2O2 Synthesis on Gold Surfaces

By means of density functional theory calculations, the reaction mechanisms of H2O2 synthesis on three low index and two stepped Au surfaces have been investigated in detail. This study shows the activation energies of five elementary reaction steps of H2O2 synthesis, which include two hydrogenation and three decomposition steps of key species, are a function of reaction energies, which observe the Bronsted–Evans–Polanyi rules on both the flat Au surfaces and the step edge sites of stepped Au surfaces. This study not only provides a simple method to estimate the reaction barriers of elementary steps of H2O2 synthesis by the reaction energies but also predicts the catalytic performances of Au nanoparticles applied in real catalysis. .

CO2 Reduction on Transition Metal (Fe, Co, Ni, and Cu) Surfaces: In Comparison with Homogeneous Catalysis

Reduction of CO2 to CO on Fe, Co, Ni, and Cu surfaces has been studied using density functional theory (DFT) methods. Three reaction steps were studied: (a) adsorption of CO2 (M + CO2 = CO2/M) (M = transition metal surface), (b) decomposition of CO2 (CO2/M = (CO + O)/M), and (c) desorption of CO ((CO + O)/M = O/M + CO). Binding energies and reaction energies were calculated using the generalized gradient approximation (GGA) via the Perdew–Burke–Ernzerhof (PBE) functional. Calculations show an interesting trend for reaction energies and total reaction barriers, as a function of metal: from Fe to Cu, reactions tend to be less exergonic; the metals earlier in the 3d series have lower total barriers for CO2 reduction. However, “overbinding” of CO2 on Fe causes a thermodynamic sink on the reaction coordinate, and Co and Ni are more favorable in terms of a smaller fluctuation in reaction energies/barriers for these elementary catalytic steps. A Bronsted–Evans–Polanyi (BEP) relationship was analyzed for C–O bond...

Kinetics of Catalytic OH Dissociation on Metal Surfaces

A tunnel mechanism of OH dissociation reaction on metal surfaces is suggested and analyzed. Expressions for the rate constant and the activation energy are obtained by calculating the transition probability on semiempirical potential energy surfaces in the framework of the nonadiabatic perturbation theory. The analysis of the transition probability leads to a linear Brønsted–Evans–Polanyi (BEP) relationship between the activation energies and the surface reaction energies (ΔI), correlated by Ea = 0.73ΔI + 18 (kcal/mol). This relationship is compared with published literature data. The effect of the electron coupling on the pre-exponential factor is discussed, and the kinetic isotope effect of hydrogen for the reaction is predicted.

Decomposition Pathways of Glycerol via C–H, O–H, and C–C Bond Scission on Pt(111): A Density Functional Theory Study

Glycerol decomposition on Pt(111) via dehydrogenation or C–C bond scission is examined with periodic density functional theory (DFT) calculations. The thermochemistry of dehydrogenation intermediates is first estimated using an empirical correlation scheme with parameters fit to selected DFT calculations; the resulting estimates for the more stable intermediates are refined with full DFT calculations. Bronsted–Evans–Polanyi (BEP) relationships for dehydrogenation and C–C bond scission reactions are developed and used to estimate the kinetics of elementary dehydrogenation and C–C bond scission steps in the reaction network. The combined thermochemical and kinetic analysis implies that glycerol dehydrogenation products at intermediate levels of dehydrogenation are the most thermochemically stable. Additionally, although C–C bond scission transition state energies are high for glycerol and for intermediates at early stages of dehydrogenation, these energies decrease as the intermediates are successively dehy...