It is shown that for all the essential bond forming and bond breaking reactions on metal surfaces, the reactivity of the metal surface correlates linearly with the reaction energy in a single universal relation. Such correlations provide an easy way of establishing trends in reactivity among the different transition metals. Keywords Density Functional Theory -Stepped surfaces -Coupling reactions -Bond breaking reactions -BEP relations -Scaling relationsTo bridge the gap between macroscopic properties of a catalyst, such as turn-over rates and selectivity and the microscopic properties obtained from electronic structure methods based on density functional theory (DFT), an in depth understanding of the underlying thermodynamics and kinetics of the corresponding metal surfaces is needed. Today, DFT has reached a level of sophistication where it can be used to describe complete catalytic reactions and hence provide an insight that pinpoints to the origin of the catalytic activity and selectivity. 1,2,3,4,5,6 However, extensive DFT calculations that eventually lead to this understanding are still computationally demanding. A simplification that connects the reactivity and selectivity of a catalytic surface to one or few descriptors is therefore extremely useful. Such a simplification, e.g. the Brønsted-Evans-Polanyi (BEP) relations, is able to show that the transition state energy of a reaction is linearly depending on the reaction energy. 7,8,9,10,11,12 * Corresponding author SLAC-PUB-14285 2 Herein, we investigate the transition state energies of a large number of essential bond breaking and forming reactions that play a key role in the catalytic transformation of a large fraction of base chemicals. The transition state energies investigated include C-C, C-O, C-N, N-O, N-N, and O-O coupling and have been calculated on different stepped surfaces of transition metals such as Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au. For a dissociation reaction (AB → A+B), the transition state energy (E ts ) is calculated by Equation (1), in which E ts/slab , E slab and E gas are the total energies of the slab with transition states, the clean slab, and the gas phase molecules relevant for the reactions, respectively. The dissociative adsorption energy (E diss ) is calculated by Equation (2), in which E A/slab and E B/slab are the total energies of the slab with adsorbates A and B, respectively.(1)All calculations were performed using the DACAPO plane-wave pseudo potential DFT code. 13 Ionic cores were described by ultrasoft pseudopotentials 14, and the Kohn-Sham one-electron valence states were expanded in a basis of plane wave functions with a cutoff energy up to 340 eV. For most adsorption systems, the surface Brillouin zone was sampled using a Monkhorst-Pack grid of size 4×4×1, while 2×3×1 was used for O 2 , and 8×6×1 was used for N 2 and NO as a test of the parameters. The self-consistent electron density was determined by iterative diagonalization of the Kohn-Sham Hamiltonian. A Fermi distribution for the population of...

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a b s t r a c tWe present density functional theory (DFT) calculations for CO hydrogenation on different transition metal surfaces. Based on the calculations, trends are established over the different monometallic surfaces, and scaling relations of adsorbates and transition states that link their energies to only two descriptors, the carbon oxygen binding energies, are constructed. A micro-kinetic model of CO hydrogenation is developed and a volcano-shaped relation based on the two descriptors is obtained for methanol synthesis. A large number of bimetallic alloys with respect to the two descriptors are screened, and CuNi alloys of different surface composition are identified as potential candidates. These alloys, proposed by the theoretical predictions, are prepared using an incipient wetness impregnation method and tested in a highpressure fixed-bed reactor at 100 bar and 250-300°C. The activity based on surface area of the active material is comparable to that of the industrially used Cu/ZnO/Al 2 O 3 catalyst. We employ a range of characterization tools such as inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis, in situ X-ray diffraction (XRD) and in situ transmission electron microscope (TEM) to identify the structure of the catalysts.

Phenomenological kinetics (PK) is widely used in the study of the reaction rates in heterogeneous catalysis, and it is an important aid in reactor design. PK makes simplifying assumptions: It neglects the role of fluctuations, assumes that there is no correlation between the locations of the reactants on the surface, and considers the reacting mixture to be an ideal solution. In this article we test to what extent these assumptions damage the theory. In practice the PK rate equations are used by adjusting the rate constants to fit the results of the experiments. However, there are numerous examples where a mechanism fitted the data and was shown later to be erroneous or where two mutually exclusive mechanisms fitted well the same set of data. Because of this, we compare the PK equations to "computer experiments" that use kinetic Monte Carlo (kMC) simulations. Unlike in real experiments, in kMC the structure of the surface, the reaction mechanism, and the rate constants are known. Therefore, any discrepancy between PK and kMC must be attributed to an intrinsic failure of PK. We find that the results obtained by solving the PK equations and those obtained from kMC, while using the same rate constants and the same reactions, do not agree. Moreover, when we vary the rate constants in the PK model to fit the turnover frequencies produced by kMC, we find that the fit is not adequate and that the rate constants that give the best fit are very different from the rate constants used in kMC. The discrepancy between PK and kMC for the model of CO oxidation used here is surprising since the kMC model contains no lateral interactions that would make the coverage of the reactants spatially inhomogeneous. Nevertheless, such inhomogeneities are created by the interplay between the rate of adsorption, of desorption, and of vacancy creation by the chemical reactions.

Unprecedented insight into the carbonylation of dimethyl ether over Mordenite is provided through the identification of ketene (CH2CO) as a reaction intermediate. The formation of ketene is predicted by detailed DFT calculations and verified experimentally by the observation of doubly deuterated acetic acid (CH2DCOOD), when D2O is introduced in the feed during the carbonylation reaction.