Jens K. Nørskov

Simple Descriptors for Predicting Fischer–Tropsch Selectivity and Activity Trends

In this work, we present a simple microkinetic model for predicting product selectivity (C1 vs C2+) trends in the Fischer–Tropsch reaction. The model is based on only three key activation barriers (carbon formation, carbon hydrogenation, and C–C coupling) and shows good agreement with experimental observations and previous theoretical trends for Ni, Co, and Ru using either CO or CO2 as the carbon source. This approach can potentially be useful for a rapid assessment of new catalysts for the Fischer–Tropsch reaction.

Spiers Memorial Lecture: Spin-mediated promotion of magnetic metal catalysts

Surface Spin Effect in Chemisorption and Catalysis: Computational Robustness

Ammonia Decomposition in the Presence of Water: A Resilient Barium Cobalt Catalyst

Thermocatalytic ammonia decomposition is a critical step in utilizing ammonia as a zero-emission fuel and energy carrier. Despite its industrial relevance, the impact of water─commonly added to ammonia to prevent tank and pipeline degradation by stress corrosion cracking─on catalyst performance remains largely unexplored. Here, we investigate the influence of trace water on the activity of Co- and Fe-based ammonia decomposition catalysts through a combined experimental and theoretical approach. Our findings reveal that while some promoted catalysts experience a detrimental activity loss, a barium-promoted cobalt catalyst demonstrates remarkable resilience, retaining most of its activity even at water concentrations up to 1%.

Field effects explain the unintuitive potential response of electrochemical oxygen evolution in acid

We show that the electrostatic destabilization due to the interaction of surface oxygen with the interfacial field on IrO 2 reduces Tafel slopes in acidic OER. This creates the erroneous impression of a non-electrochemical rate limiting step.

CO Methanation over Ni–Fe Alloy Catalysts: An Inverse Design Problem

We propose an approach to solve the inverse design problem in heterogeneous catalysis in which the goal is to find a material composition and structure that will maximize the active surface site under reaction conditions with knowledge of the active site motif being given. Taking CO methanation over Ni-Fe bimetallic alloys as our basis catalyst systems, we aim to identify a Ni-Fe bulk/surface composition that can provide the highest activity under reaction conditions. First, the stability of various (211) surfaces with different surface and bulk compositions is studied, especially if the CO adsorption could induce surface segregation has been well studied since CO is found to dominantly cover the surface during CO methanation. Due to a similar binding strength of CO over Ni and Fe, we did not observe surface segregation induced by CO adsorption. Reaction kinetics on the corresponding stable surfaces are obtained through coverage- and surface-consistent MKM. The 4-Fe Ni3Fe(211) surface site, which corresponds to 4 Fe atoms on the surface, is the most active site among all the stable surfaces. This high activity is attributed to the presence of a pure Ni step site and an adjacent Fe site, which are particularly active for CO activation (CO + H → COH) and dissociation (COH → C + OH), respectively. Additional calculations on reaction barriers for these two rate-controlling steps on similar Ni3Fe(211) surfaces confirmed that the 1-Fe Ni3Fe(211) surface, despite being less stable, shows lower reaction barriers, suggesting the potential for further activity enhancement. Consequently, we propose that optimizing Ni1-xFex catalysts for CO methanation may involve synthesizing Ni3Fe catalysts with a focus on stabilizing the active site motif identified under the reaction conditions. The proposed approach offers a strategic pathway for researchers aiming to solve the inverse design problem for catalysts in other reaction systems.

Spin-mediated promotion of Co catalysts for ammonia synthesis

Over the past two decades, there has been growing interest in developing catalysts to enable Haber-Bosch ammonia synthesis under milder conditions than currently pertain. Rational catalyst design requires theoretical guidance and clear mechanistic understanding. Recently, a spin-mediated promotion mechanism was proposed to activate traditionally unreactive magnetic materials such as cobalt (Co) for ammonia synthesis by introducing hetero metal atoms bound to the active site of the catalyst surface. We combined theory and experiment to validate this promotion mechanism on a lanthanum (La)/Co system. By conducting model catalyst studies on Co single crystals and mass-selected Co nanoparticles at ambient pressure, we identified the active site for ammonia synthesis as the B5 site of Co steps with La adsorption. The turnover frequency of 0.47 ± 0.03 per second achieved on the La/Co system at 350°C and 1 bar surpasses those of other model catalysts tested under identical conditions.

Phenol as proton shuttle and buffer for lithium-mediated ammonia electrosynthesis

Ammonia is a crucial component in the production of fertilizers and various nitrogen-based compounds. Now, the lithium-mediated nitrogen reduction reaction (Li-NRR) has emerged as a promising approach for ammonia synthesis at ambient conditions. The proton shuttle plays a critical role in the proton transfer process during Li-NRR. However, the structure-activity relationship and design principles for effective proton shuttles have not yet been established in practical Li-NRR systems. Here, we propose a general procedure for verifying a true proton shuttle and established design principles for effective proton shuttles. We systematically evaluate several classes of proton shuttles in a continuous-flow reactor with hydrogen oxidation at the anode. Among the tested proton shuttles, phenol exhibits the highest Faradaic efficiency of 72 ± 3% towards ammonia, surpassing that of ethanol, which has been commonly used so far. Experimental investigations including operando isotope-labelled mass spectrometry proved the proton-shuttling capability of phenol. Further mass transport modeling sheds light on the mechanism.

Theory-guided development of a barium-doped cobalt catalyst for ammonia decomposition

This work describes the theory-guided design and experimental validation of a barium-doped cobalt catalyst for ammonia decomposition.

Characterization of adsorption sites on IrO ₂ via temperature programmed O ₂ desorption simulations

We identify a new adsorption site related to the formation of steps on IrO 2 (110), that is essential for reproducing the experimental TPD.

Activity And Stability of Single‐ And Di‐Atom Catalysts for the O 2 Reduction Reaction

reduction reaction (ORR) are needed for the advancement of renewable energy technologies. In this study, we designed a computational catalyst-screening method to identify single and di-atom metal dopants from first-row transition elements supported on defect-containing nitrogenated graphene surfaces for the ORR. Based on formation-energy calculations and micro-kinetic modelling of reaction pathways using intermediate binding free energies, we have identified four potentially interesting single-atom catalysts (SACs) and fifteen di-atom catalysts (DACs) with relatively high estimated catalytic activity at 0.8 V vs RHE. Among the best SACs, MnNC shows high stability in both acidic and alkaline media according to our model. For the DACs, we found four possible candidates, MnMn, FeFe, CoCo, and MnNi doped on quad-atom vacancy sites having considerable stability over a wide pH range. The remaining SACs and DACs with high activity are either less stable or show a stability region at an alkaline pH.

Activity And Stability of Single‐ And Di‐Atom Catalysts for the O2 Reduction Reaction

Efficient and inexpensive catalysts for the O2 reduction reaction (ORR) are needed for the advancement of renewable energy technologies. In this study, we designed a computational catalyst‐screening method to identify single and di‐atom metal dopants from first‐row transition elements supported on defect‐containing nitrogenated graphene surfaces for the ORR. Based on formation‐energy calculations and micro‐kinetic modelling of reaction pathways using intermediate binding free energies, we have identified four potentially interesting single‐atom catalysts (SACs) and fifteen di‐atom catalysts (DACs) with relatively high estimated catalytic activity at 0.8 V vs RHE. Among the best SACs, MnNC shows high stability in both acidic and alkaline media according to our model. For the DACs, we found four possible candidates, MnMn, FeFe, CoCo, and MnNi doped on quad‐atom vacancy sites having considerable stability over a wide pH range. The remaining SACs and DACs with high activity are either less stable or show a stability region at an alkaline pH.

Chain ether-based electrolyte enables long-term continuous ammonia electrosynthesis

Ammonia is essential to the fertilizer and chemical industries and is seen as a carbon-free fuel1. The ammonia electrosynthesis from nitrogen under ambient conditions is an attractive alternative to the centralized Haber-Bosch process2,3. The lithium-mediated nitrogen reduction (Li-NRR) has been demonstrated as a promising approach for continuous-flow ammonia electrosynthesis, where nitrogen reduction is coupled with hydrogen oxidation4. This provides a genuine pathway for converting nitrogen and hydrogen into ammonia, but the long-term ammonia production is impeded by the polymerization and volatility of ring ether-based solvent, tetrahydrofuran (THF, with a boiling point of 66 °C), in a continuous-flow electrolyzer. Here we show that a chain ether-based electrolyte enables long-term continuous ammonia synthesis. We find that a chain ether-based solvent offers not only non-polymerization properties and high boiling point (162 °C) but also the formation of a compact solid-electrolyte interphase (SEI) layer on the gas diffusion electrode (GDE), facilitating the release of produced ammonia in the gas phase and ensuring long-term stability of the electrolyte. We demonstrate 300 hours continuous operation in a flow electrolyzer at 1 bar and room temperature, and achieve a current-to-ammonia efficiency of 64% (repeated twice) with unprecedented gas phase ammonia of ~98%. Our work highlights the crucial role of the solvent in long-term continuous ammonia synthesis, and these findings will guide the development of a durable and efficient process for sustainable ammonia production.

Spin Effects in Chemisorption and Catalysis

In this work, we show using density functional theory calculations that controlling the spin state of the surface of magnetic metals has a substantial effect on their chemical properties. For a range of adsorbates, the adsorption energy is shown to be stronger on non-spin polarized surfaces than on spin polarized ground state surfaces. This is true for Fe, Co, and Ni surfaces, and the result is the same for three commonly used exchange–correlation functionals. We further discuss the origin of the effect in terms of the surface electronic structure and show that a simple model based on the d-band model of adsorption can explain the effect. Finally, we discuss how spin effects may be used to control surface reactivity and provide guidance on how to alter the surface spin state, e.g., adding a metal promotor.

Continuous-flow electrosynthesis of ammonia by nitrogen reduction and hydrogen oxidation

Ammonia is a critical component in fertilizers, pharmaceuticals, and fine chemicals and is an ideal, carbon-free fuel. Recently, lithium-mediated nitrogen reduction has proven to be a promising route for electrochemical ammonia synthesis at ambient conditions. In this work, we report a continuous-flow electrolyzer equipped with 25-square centimeter-effective area gas diffusion electrodes wherein nitrogen reduction is coupled with hydrogen oxidation. We show that the classical catalyst platinum is not stable for hydrogen oxidation in the organic electrolyte, but a platinum-gold alloy lowers the anode potential and avoids the decremental decomposition of the organic electrolyte. At optimal operating conditions, we achieve, at 1 bar, a faradaic efficiency for ammonia production of up to 61 ± 1% and an energy efficiency of 13 ± 1% at a current density of -6 milliamperes per square centimeter.

Reversible Atomization and Nano-Clustering of Pt as a Strategy for Designing Ultra-Low-Metal-Loading Catalysts

Noble metal-based catalysts have numerous industrial uses, and maximum utilization of the precious metals by lowering the metal loading is of significant interest in heterogeneous catalysis research. However, lowering the metal loading could lead to single-atom metal species formation, which may not be active for important reactions like propylene oxidation. We report a way to drastically reduce precious metal loading of catalysts by judiciously choosing an active metal/support pair and using the reversible atomization–nanoparticulate formation of transition metal on a high-surface area support. Here, Pt and MgAl 2 O 4 are used as the transition metal and high-surface area support, respectively. Through catalytic testing and characterization using scanning transmission electron microscopy and synchrotron X-ray absorption spectroscopy, a reversible change between atomization and nano-cluster formation under oxidizing and reducing conditions has been found. Via density functional theory, favorable sites for reversible Pt adsorption are identified, including ionic Pt 4+ sites that can serve to nucleate nanoclusters. Catalytic reaction modeling also rationalizes the catalytic inertness of atomic Pt sites. Finally, a re-activation mechanism for the atomized Pt based on gases present during reaction has been formulated and demonstrated.

Electrosynthesis of ammonia with high selectivity and high rates via engineering of the solid-electrolyte interphase

Ammonia is a large-scale commodity essential to fertilizer production, but the Haber-Bosch process leads to massive emissions of carbon dioxide. Electrochemical ammonia synthesis is an attractive alternative pathway, but the process is still limited by low ammonia production rate and faradaic efficiency. Herein, guided by our theoretical model, we present a highly efficient lithium-mediated process enabled by using different lithium salts, leading to the formation of a uniform solid-electrolyte interphase (SEI) layer on a porous copper electrode. The uniform lithium-fluoride-enriched SEI layer provides an ammonia production rate of 2.5 ± 0.1 μmol s⁻¹ cmgeo ⁻² at a current density of -1 A cmgeo ⁻² with 71% ± 3% faradaic efficiency under 20 bar nitrogen. Experimental X-ray analysis reveals that the lithium tetrafluoroborate electrolyte induces the formation of a compact and uniform SEI layer, which facilitates homogeneous lithium plating, suppresses the undesired hydrogen evolution as well as electrolyte decomposition, and enhances the nitrogen reduction.

Strategies for Modulating the Catalytic Activity and Selectivity of Manganese Antimonates for the Oxygen Reduction Reaction

Strategies for improving the performance of nonprecious metal catalysts for the oxygen reduction reaction (ORR) can facilitate the cost-effective deployment of fuel cell devices. Electrocatalyst performance is typically improved via two approaches: increasing the number of active sites and increasing the intrinsic activity of the active site. Herein, we utilize these two methods of improving performance for MnSb2O6, which we have recently shown to be a promising ORR catalyst due to improvements in per-metal-site activity in the antimonate framework. First, electrode engineering is used to investigate the role of mass and conductive support loading in the observed ORR performance and selectivity. The apparent 2-electron selectivity is found to decrease with increases in mass and/or conductive support loading, indicating that rotating ring disk electrode studies do not necessarily measure the intrinsic selectivity of the catalyst. Second, theoretical calculations are used to identify Cr, Fe, and Ni as promising first-row transition metals for improving the intrinsic activity of MnSb2O6. Experimentally, the addition of Cr results in 3-fold and 2-fold increases in the mass and specific activities at 0.7 V vs the reversible hydrogen electrode, respectively. This enhancement is attributed to the modulation of the active site structure and Mn oxidation state with the addition of Cr. Through these studies, we gain insight into the intrinsic and extrinsic factors that govern ORR performance.

Limits to scaling relations between adsorption energies?

Linear scaling relations have led to an understanding of trends in catalytic activity and selectivity of many reactions in heterogeneous and electro-catalysis. However, linear scaling between the chemisorption energies of any two small molecule adsorbates is not guaranteed. A prominent example is the lack of scaling between the chemisorption energies of carbon and oxygen on transition metal surfaces. In this work, we show that this lack of scaling originates from different re-normalized adsorbate valence energies of lower-lying oxygen vs higher-lying carbon. We develop a model for chemisorption of small molecule adsorbates within the d-band model by combining a modified form of the Newns-Anderson hybridization energy with an effective orthogonalization term. We develop a general descriptor to a priori determine if two adsorbates are likely to scale with each other.

A spin promotion effect in catalytic ammonia synthesis

The need for efficient ammonia synthesis is as urgent as ever. Over the past two decades, many attempts to find new catalysts for ammonia synthesis at mild conditions have been reported and, in particular, many new promoters of the catalytic rate have been introduced beyond the traditional K and Cs oxides. Herein, we provide an overview of recent experimental results for non-traditional promoters and develop a comprehensive model to explain how they work. The model has two components. First, we establish what is the most likely structure of the active sites in the presence of the different promoters. We then show that there are two effects dictating the catalytic activity. One is an electrostatic interaction between the adsorbed promoter and the N-N dissociation transition state. In addition, we identify a new promoter effect for magnetic catalysts giving rise to an anomalously large lowering of the activation energy opening the possibility of finding new ammonia synthesis catalysts.