To provide guidelines to accelerate the Haber–Bosch (HB) process for synthesis of ammonia from hydrogen and nitrogen, we used Quantum Mechanics (QM) to determine the reaction mechanism and free energy reaction barriers under experimental reaction conditions (400 °C and 20 atm) for all 10 important surface reactions on the Fe(211)R surface.

The heat ow across a metal/polymer interface is a very important problem in many modern engineering applications. A thermal joint conductance model that employs the surface mechanics of a contact interface in conjunction with an existing elastic thermal contact conductance model was developed. In developing the model, an elastic contact hardness term was derived to predict the actual contact area of a metal/polymer interface under loading. The model predicts a microscopic resistance region where the interface resistance is dominant and a bulk resistance region where the thermal conductivity of the polymer is dominant. An experimental apparatus was fabricated, and a successful experimental program was conducted. New experimental data were gathered on different polymeric specimens over a pressure range of 138-2758 kPa (20-400 psi). The experimental data were compared to the proposed thermal joint conductance model. It was found that the proposed model predicted the data quite well. The data followed the predicted trends for both the microscopic and bulk resistance regions. Nomenclature A a= apparent area of contact, m 2 A r = real area of contact, m 2 a c = contact radius, m a 0 = Hertzian contact radius, m c = half-width of plane contact area, melastic modulus of polymer, Pa E s = elastic modulus of substrate, Pa H c = contact microhardness, Pa H e = Mikic elastic hardness (E 0 = p 2)£ m, Pa H ep = polymer elastic hardness, Pa h bulk = thermal bulk conductance, W/m 2 K h c = thermal contact conductance, W/m 2 K h e = dimensionless elastic conductance h j = thermal joint conductance, W/m 2 K h j exp = experimentally calculated joint conductance, W/m 2 K h micro = thermal microscopic conductance, W/m 2 K J .t / = creep compliance k ux = thermal conductivity of ux meter, W/m K k p = thermal conductivity of polymer, W/m K k s = harmonic mean thermal conductivity, W/m K L = load, N m ab = mean absolute asperity slope, rad n = number of contact spots per unit area of apparent contact, m ¡2 P = apparent pressure, Pa P=H c = dimensionless plastic contact pressure P=H e = dimensionless elastic contact pressure P m = mean pressure at interface, Pa Q = heat rate, W q = heat ux through ux meter, W/m 2 R b = bulk thermal resistance, K/W R g;1 = gap resistance at interface 1, K/W R g;2 = gap resistance at interface 2, K/W R j = joint resistance, K/W R micro = microscopic thermal resistance, K/W R t;c = contact resistance, K/W R 1 = thermal resistance for upper interface, K/W R 2 = thermal resistance for lower interface, K/W T c = temperature of specimen, K T sl = temperature of lower interface of specimen, K T su = temperature of upper interface of specimen, K T 1 = temperature at surface 1, K T 2 = temperature at surface 2, K t = elastic layer (polymer) thickness, m t f = polymer thickness after loading, m t 0 = polymer thickness before loading, m t ¤ = critical polymer thickness, m Y = separation distance between contacting surfaces, m Y .t / = relaxation modulus " p = strain on polymer in the vertical directioņ = dimensionle...

To discover more efficient industrial catalysts for ammonia synthesis via the Haber-Bosch (HB) process, we employed quantum-mechanics (QM)-based hierarchical high throughput catalyst screening (HHTCS) to test a wide group of elements (34) as candidates to dope the Fe(111) catalyst subsurface. The QM freeenergy reaction network of HB over Fe(111) yields ten barriers as potentially rate-determining, of which we select four as prototypical, arrange them hierarchically, and define a corresponding set of screening criteria, which we then use to screen candidate catalysts. This leads to two promising candidates (Co and Ni), from which we selected the most promising (Ni) for a complete QM and kinetic study. The kinetic Monte Carlo (kMC) simulations predict a 16-fold increase in HB turn over frequency (TOF) for the Nidoped catalyst compared to the pure Fe(111) surface under realistic conditions. The 16-fold increase in HB turn over frequency (TOF) is a significant improvement and may trigger future experimental studies to validate our prediction. This TOF improvement could lead to similar reaction rates as with pure Fe but at areaction temperature decreased by 100 degrees from 773 to 673 K and a total reactant pressure decreased by 6 times from 201 atm to 34 atm. We interpret the reasons underlying this improvement using Valence Bond and kinetic analyses. We suggest this Ni-doped Fe(111) catalyst as a candidate to reduce the world energy consumption for the HB process while satisfying future needs for energy and environment.

In order to improve efficiency of ammonia synthesis using the Haber−Bosch (HB) process with Fe-based catalysts, we employed quantum mechanics (QM)-based hierarchical high-throughput catalyst screening (HHTCS) of 49 possible metal dopants. Here, we consider the Fe( 211) surface (one of the two most active iron catalyst facets) to identify dopants that dramatically increase the turnover frequency (TOF) for HB synthesis. We found that under HB conditions, this surface reconstructs to form the Fe(211)R missing-row surface. Focusing on dopants with a strong preference for the subsurface site, we found that Co is the most promising candidate among the 49. We then examined the full reaction pathway on this Co-doped Fe(211)R surface, considering all 19 important 2 × 2 configurations and calculated the free-energy barriers (ΔG ∫ ) for all 12 important reaction steps. At 673 K and 20 atm, we find a decrease, δ(ΔG ∫ ) = −0.19 eV, in the overall reaction free-energy barrier for the Co-doped case. We then carried out kinetic Monte Carlo simulations for 60−120 min using 100 replicas with the full reaction path using rates from QM free-energy reaction barriers to predict that the TOF for the Co-doped surface increases by a factor of 2.8 with respect to the undoped Fe(211)R surface. Thus, the Co-doped Fe(211)R system could lower the extreme HB pressure of 200 atm to ∼40 atm at 773 K while maintaining the same TOF as that of undoped Fe(211)R. We conclude that Co dopants in the Fe catalyst could significantly improve the catalytic efficiency of ammonia synthesis under industrial conditions. This excellent performance of the Co-doped system is explained in terms of a surface spin analysis on the N 2 -bonded configurations that show how Co dopants shift the N 2 surface-binding mode. This demonstrates that metal surface spins can be used as quantitative descriptors to understand reaction energetics. This study demonstrates that the HHTCS kinetic analysis of the free-energy reaction path in terms of essential configurations can enable discovery of the salient barriers to overcome and best dopant candidates for further improvements.

Boron carbide is super-strong and has many important engineering applications such as body armor and cutting tools. However, the extended applications of boron carbide have been limited by its low fracture toughness arising from anomalous brittle failure when subjected to hypervelocity impact or under high pressure. This abnormal brittle failure is directly related to the formation of a tiny amorphous shear band of 2–3 nm in width and several hundred nm in length. In this Perspective, we discuss mitigating the amorphous shear bands in boron carbide from various strategies including microalloying, grain boundary engineering, stoichiometry control, and the addition of a second phase. Combined with recent theoretical and experimental studies, we discuss strategies that can be applied in synthesizing and producing boron carbide-based materials with improved ductility by suppressing the formation of the amorphous shear band.