The role of potassium in the catalytic synthesis of ammonia

Ertl, G.; Weiss, M.; Lee, S.B.

doi:10.1016/0009-2614(79)80595-3

Cited by 212 publications

(102 citation statements)

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“…Subsequently, during the late 1970s and early 1980s, Gerhard Ertl undertook the series of single-crystal uhv studies relating to ammonia synthesis (7)(8)(9)(10)(11) for which (in large part) he was later to be awarded the Nobel Prize in Chemistry (2007). That work revealed initial dissociative sticking probabilities for N 2 in the range 10 − 7-10 − 6 for Fef111g, Fef110g, and Fef100g, enhanced in the presence of a K promoter, suggesting once again that adsorption of nitrogen (step ii above) is likely to be rate-determining.…”

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confidence: 99%

Hydrogenation of N over Fe{111}

Iyngaran

Madden

Jenkins

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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Over the past five decades, ultra high vacuum (uhv) techniques applied to well-defined single-crystal samples (the "surface science paradigm") have transformed our understanding of fundamental surface chemistry. To translate this success to the world of realistic heterogeneous catalysis, however, requires one seriously to address the fact that real heterogeneous catalysts usually operate under near-ambient or higher pressures. Nevertheless, the surface science paradigm can undoubtedly provide crucial insights into catalytic processes, so long as care is exercised in the design of experiments. Forging a secure link between two radically different pressure regimes is the major challenge, which we illustrate here with reference to the vitally important ammonia synthesis reaction, achieved industrially only under extremely high pressure.Auger spectroscopy | catalytic ammonia synthesis | surface chemistry I f uhv experiments are ever to map onto realistic catalytic conditions, it is often essential that relatively high surface coverages are maintained, implying that experiments must be conducted at much lower temperatures than are industrially employed. Structural, vibrational, and thermodynamic observations may then readily be made relating to reactants, intermediates, and products at relevant surface concentrations, but the low temperatures imply that kinetic information may be unobtainable due to slow reaction rates. Theoretical multiscale modeling of reaction kinetics (incorporating, for example, quantum chemistry, microkinetic simulation and/or computational fluid dynamics) provides one possible bridge across the so-called "pressure gap," with uhv single-crystal experiments benchmarking one end of the route and high-area catalytic studies the other.An alternative, however, is to seek purely experimental techniques and methodologies that will allow the best features of the surface science paradigm to be retained when moving beyond uhv conditions. For example, techniques such as X-ray photoemission spectroscopy (XPS), atomic force microscopy (AFM), and reflection absorption infrared spectroscopy (RAIRS) can all be applied (albeit subject to technical modifications) at near-ambient pressures. Techniques based upon supersonic molecular beams (SMB) are also relevant here, because the effective pressure where the beam impinges upon the sample may be quite high, while the overall pressure of the chamber remains in the uhv range.In the present paper, we make use of a "third way" to bridge the pressure gap, entailing the alternation of uhv and nearambient pressure conditions within a single experiment. Surface reactions occur with reasonable rates during the higher-pressure periods, because appropriate surface coverages of all reactants are maintained even at elevated temperature, and surface science measurements are then carried out during the uhv interludes, when electron spectroscopy becomes feasible.Turning to the specific catalytic process that we address in this work, one may break down the necessary steps for ammo...

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confidence: 99%

Hydrogenation of N over Fe{111}

Iyngaran

Madden

Jenkins

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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“…It has been shown that dissociation of species such as N 2 or NO on Fe͑100͒ and Rh͑100͒, as well as oxidation of CO on Ni͑111͒, is promoted upon alkali adsorption. [1][2][3] Additionally, the formation of alkali-induced quantum-well states, which may modify the surface reactivity, has been observed in Na/ Cu͑111͒ and Cs/ Cu͑111͒ systems. [4][5][6] Thus, the detailed understanding of alkali-induced properties is necessary for facilitating the design of a new efficient catalyst.…”

Section: Introductionmentioning

confidence: 99%

“…[1][2][3] Even small amounts of alkali-metal atoms adsorbed on noble or transition metals enhance the reactivity of a catalyst toward various reactions. It has been shown that dissociation of species such as N 2 or NO on Fe͑100͒ and Rh͑100͒, as well as oxidation of CO on Ni͑111͒, is promoted upon alkali adsorption.…”

Section: Introductionmentioning

confidence: 99%

Substrate-mediated interaction and electron-induced diffusion of single lithium atoms on Ag(001)

et al. 2007

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The adsorption properties and the mechanism of induced diffusion of single Li atoms on Ag͑001͒ have been investigated at 5 K by means of the low-temperature scanning-tunneling microscopy. On the basis of Li-Li pair distances, we have observed that there is no preferential adsorption site on Ag͑001͒. Li adatoms form pairs with one preferred adatom distance, most likely due to long-range interaction between Li adatoms mediated by electrons from the bulk. The manipulation experiments show that diffusion of single Li adatoms can be induced upon electron transfer into an unoccupied electronic state connected to a single Li adatom. The existence of such Li-induced state is also confirmed by spectroscopic measurements.

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“…Chemisorption occurring through nitrogen-hydrogen chemical bonding is the most likely adsorption mechanism. Certainly there is a precedent for consideration of these types of chemisorptive catalytic reactions, as it has been found Franzblau and Popp (1989) Field study 3.00 × 10 27 4981.73 that the rate of catalytic ammonia synthesis is primarily determined by nitrogen chemisorption (Klimisch and Larson, 1975); many other reactions are also dictated by nitrogen chemisorption (Shinn, 1990;Wovchko and Yates, 1996;Ertl et al, 1979). The greatest amount of adsorption per unit of ice particles probably occurs with the dendrite crystal habit, since dendrites have the largest specific surface area (Fig.…”

Section: Introductionmentioning

confidence: 99%

Possible catalytic effects of ice particles on the production of NO<sub>x</sub> by lightning discharges

Peterson

Beasley

2011

Atmos. Chem. Phys.

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Abstract.It is well known that lightning produces NO x as a result of the high temperatures in discharge channels. Since most viable proposed electrification mechanisms involve ice crystals, it is reasonable to assume that lightning discharge channels frequently pass through fields of ice particles of various kinds. We address the question of whether ice crystals may serve as catalysts for the production of NO x by lightning discharges. If so, and if the effect is large, it would need to be taken into account in estimates of global NO x production by lightning. In this theoretical study, we make a series of plausible assumptions about the temperature and concentration of reactant species in the environment of discharges and we postulate a mechanism by which ice crystals are able to adsorb nitrogen atoms. We then compare production rates between uncatalyzed and catalyzed reactions at 2000 K, 3000 K, and 4000 K, which are reasonable temperatures in lightning channels as they cool down. Ice crystal catalysis is expected to produce 2.7 times more NO than if ice crystals were not present. Catalyzed NO production rates are greater at 2000 K, whereas uncatalyzed production rates are greater at 4000 K. Thus, temperatures that favor rapid NO production without ice crystals adsorbing nitrogen atoms are unfavorable for NO production in the presence of ice crystals, and vice versa. The density of atmospheric ice crystals is much larger at 10 km where intracloud (IC) flashes peak than at 5 km where cloud to ground (CG) flashes peak, thus catalytic processes are expected to be more important for IC flashes than CG flashes, perhaps explaining a portion of the discrepancy in IC and CG production rates.

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The role of potassium in the catalytic synthesis of ammonia

Cited by 212 publications

References 7 publications

Hydrogenation of N over Fe{111}

Hydrogenation of N over Fe{111}

Substrate-mediated interaction and electron-induced diffusion of single lithium atoms on Ag(001)

Possible catalytic effects of ice particles on the production of NO<sub>x</sub> by lightning discharges

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The role of potassium in the catalytic synthesis of ammonia

Cited by 212 publications

References 7 publications

Hydrogenation of N over Fe{111}

Hydrogenation of N over Fe{111}

Substrate-mediated interaction and electron-induced diffusion of single lithium atoms on Ag(001)

Possible catalytic effects of ice particles on the production of NO&lt;sub&gt;x&lt;/sub&gt; by lightning discharges

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Possible catalytic effects of ice particles on the production of NO<sub>x</sub> by lightning discharges