Long-Chain Terminal Alcohols through Catalytic CO Hydrogenation

Chemical Orderings in CuCo Nanoparticles: Topological Modeling Using DFT Calculations

The orderings of atoms in bimetallic 1.6-2.1 nm-large CuCo nanoparticles, important as catalytic and magnetic materials, were studied using a combination of DFT calculations with a topological approach. The structure and magnetism of Cu50Co151, Cu101Co100, Cu151Co50, and Cu303Co102 nanoparticles; their resistance to disintegrating into separate Cu and Co species; as well as the exposed surface sites, were quantified and analyzed, showing a clear preference for Cu atoms to occupy surface positions while the Co atoms tended to form a compact cluster in the interior of the nanoparticles. The surface segregation of Co atoms that are encapsulated by less-active Cu atoms, induced by the adsorption of CO molecules, was already enabled at a low coverage of adsorbed CO, providing the energy required to displace the entire compact Co species inside the Cu matrices due to a notable adsorption preference of CO for the Co sites over the Cu ones. The calculated adsorption energies and vibrational frequencies of adsorbed CO should be helpful indicators for experimentally monitoring the nature of the surface sites of CuCo nanoparticles, especially in the case of active Co surface sites emerging in the presence of CO.

Active learning streamlines development of high performance catalysts for higher alcohol synthesis

Developing efficient catalysts for syngas-based higher alcohol synthesis (HAS) remains a formidable research challenge. The chain growth and CO insertion requirements demand multicomponent materials, whose complex reaction dynamics and extensive chemical space defy catalyst design norms. We present an alternative strategy by integrating active learning into experimental workflows, exemplified via the FeCoCuZr catalyst family. Our data-aided framework streamlines navigation of the extensive composition and reaction condition space in 86 experiments, offering >90% reduction in environmental footprint and costs over traditional programs. It identifies the Fe65Co19Cu5Zr11 catalyst with optimized reaction conditions to attain higher alcohol productivities of 1.1 gHA h-1 gcat-1 under stable operation for 150 h on stream, a 5-fold improvement over typically reported yields. Characterization reveals catalytic properties linked to superior activities despite moderate higher alcohol selectivities. To better reflect catalyst demands, we devise multi-objective optimization to maximize higher alcohol productivity while minimizing undesired CO2 and CH4 selectivities. An intrinsic trade-off between these metrics is uncovered, identifying Pareto-optimal catalysts not readily discernible by human experts. Finally, based on feature-importance analysis, we formulate data-informed guidelines to develop performance-specific FeCoCuZr systems. This approach goes beyond existing HAS catalyst design strategies, is adaptable to broader catalytic transformations, and fosters laboratory sustainability.

Intermetallic Ni3Ga1 Catalyst for Efficient Ammonia Reforming of Light Alkane

Ammonia reforming of light alkane is conventionally employed for HCN production where coproduct H2 is burned for heating owing to the high reaction temperature (1200 °C) of such a highly endothermic process. Here, we show that a Ni3Ga1 intermetallic compound (IMC) catalyst is highly efficient for such a reaction, realizing efficient conversion of C1-C3 alkanes at 575-750 °C. This makes it feasible for on-purpose COx-free H2 production assuming that ammonia, as an H2 carrier, is ubiquitously available from renewable energy. At 650 °C and an alkane/ammonia ratio of 1/2, ethane and propane conversion of ∼20% and methane conversion of 13% were obtained (with nearly 100% HCN selectivity for methane and ethane) over the unsupported Ni3Ga1 IMC, which also shows high stability due to the absence of coke deposition. This breakthrough is achieved by employing a stoichiometric Ni3Ga1 mixed oxalate solid solution as the precursor for the Ni3Ga1 IMC.

The oscillating Fischer-Tropsch reaction

The mechanistic steps that underlie the formation of higher hydrocarbons in catalytic carbon monoxide (CO) hydrogenation at atmospheric pressure over cobalt-based catalysts (Fischer-Tropsch synthesis) have remained poorly understood. We reveal nonisothermal rate-and-selectivity oscillations that are self-sustained over extended periods of time (>24 hours) for a cobalt/cerium oxide catalyst with an atomic ratio of cobalt to cerium of 2:1 (Co2Ce1) at 220°C and equal partial pressures of the reactants. A microkinetic mechanism was used to generate rate-and-selectivity oscillations through forced temperature oscillations. Experimental and theoretical oscillations were in good agreement over an extended range of reactant pressure ratios. Additionally, phase portraits for hydrocarbon production were constructed that support the thermokinetic origin of our rate-and-selectivity oscillations.

A Review of Theoretical Studies on Carbon Monoxide Hydrogenation via Fischer-Tropsch Synthesis over Transition Metals

The increasing demand for clean fuels and sustainable products has attracted much interest in the development of active and selective catalysts for CO conversion to desirable products. This review maps the theoretical progress of the different facets of most commercial catalysts, including Co, Fe, Ni, Rh, and Ru. All relevant elementary steps involving CO dissociation and hydrogenation and their dependence on surface structure, surface coverage, temperature, and pressure are considered. The dominant Fischer-Tropsch synthesis mechanism is also explored, including the sensitivity to the structure of H-assisted CO dissociation and direct CO dissociation. Low-coordinated step sites are shown to enhance catalytic activity and suppress methane formation. The hydrogen adsorption and CO dissociation mechanisms are highly dependent on the surface coverage, in which hydrogen adsorption increases, and the CO insertion mechanism becomes more favorable at high coverages. It is revealed that the chain-growth probability and product selectivity are affected by the type of catalyst and its structure as well as the applied temperature and pressure.

ZrO2-Promoted Cu-Co, Cu-Fe and Co-Fe Catalysts for Higher Alcohol Synthesis

The development of efficient catalysts for the direct synthesis of higher alcohols (HA) via CO hydrogenation has remained a prominent research challenge. While modified Fischer-Tropsch synthesis (m-FTS) systems hold great potential, they often retain limited active site density under operating conditions for industrially relevant performance. Aimed at improving existing catalyst architectures, this study investigates the impact of highly dispersed metal oxides of Co-Cu, Cu-Fe, and Co-Fe m-FTS systems and demonstrates the viability of ZrO2 as a general promoter in the direct synthesis of HA from syngas. A volcano-like composition-performance relationship, in which 5-10 mol % ZrO2 resulted in maximal HA productivity, governs all catalyst families. The promotional effect resulted in a 2.5-fold increase in HA productivity for the optimized Cu1Co4@ZrO2-5 catalyst (Cu:Co = 1:4, 5 mol % ZrO2) compared to its ZrO2-free counterpart and placed Co1Fe4@ZrO2-10 among the most productive systems (345 mgHA h-1 gcat-1) reported in this category under comparable operating conditions, with stable performance for at least 300 h. ZrO2 assumes an amorphous and defective nature on the catalysts, leading to enhanced H2 and CO activation, facilitated formation of metallic and carbide phases, and structural stabilization.

A review of Co/Co2C-based catalysts in Fischer-Tropsch synthesis: from fundamental understanding to industrial applications

Fischer-Tropsch synthesis (FTS), which provides a green route to the production of clean fuels and fine chemicals, represents some significant applications of catalytic materials and processes in the chemical industry. FTS reactions show a diversity of mechanisms, involve various catalytic materials, and offer options for continuous investigation. Cobalt-based catalysts have been widely used for Fischer-Tropsch synthesis both in academia and in industry. This mini-review will focus on relevant research achievements in cobalt-based FTS catalysts by our group in the Dalian Institute of Chemical Physics (DICP). Specific contents will include the development of Co/Co₂C-based nano-catalysts (i) for the highly selective synthesis of clean fuels over Co-based catalysts supported by carbon materials and (ii) for the synthesis of linear α-alcohols and olefins over Co-Co₂C-based catalysts supported by carbon materials. The direct synthesis of linear α-alcohols from syngas using a Co-Co₂C/AC catalyst is highlighted. The innovative work of FTS using activated carbon (AC)-supported Co/Co₂C-based nano-catalysts could bring some insight into new FTS catalyst designs.

LaCo1-x-yCuxTiyO3/KIT-6 perovskites: synthesis and catalytic behavior in syngas conversion to higher alcohols

Highly dispersed LaCo_1-x-yCu_xTi_yO₃/KIT-6 perovskites were synthesized by the citrate method with inert mesoporous KIT-6 addition. The KIT-6 matrix was removed by dissolution in 7% NaOH aqueous solution. The dispersity of perovskites probably varies depending on the largest cation and its content at the B position of the perovskite ABO3 structure. The Co_S=2³⁺/Co_S=0³⁺ ratio increases with the increase in copper content and in the presence of Ti⁴⁺. It may be explained by the compensation of the distortion of the perovskite structure. The maximum syngas conversion is achieved at n_Co/n_Cu = 7/3. At a higher copper content, the activity of the samples decreases due to the formation of large copper particles (up to 40 nm) in the course of the reduction. The selectivity for alcohols increases with an increase in the proportion of copper and reaches maximum values at a ratio of n_Co/n_Cu close to 1. The distribution of alcohols is the same for all samples, except for LaCo_0.35Cu_0.35Ti_0.3O₃/KIT-6. It can be assumed that the synthesis of alcohols proceeds on bimetallic CoCu particles 3 nm in size and cobalt particles 4-6 nm in size, most likely enriched with copper on the surface.

Direct Conversion of Syngas to Higher Alcohols via Tandem Integration of Fischer-Tropsch Synthesis and Reductive Hydroformylation

The selective conversion of syngas to higher alcohols is an attractive albeit elusive route in the quest for effective production of chemicals from alternative carbon resources. We report the tandem integration of solid cobalt Fischer–Tropsch and molecular hydroformylation catalysts in a one‐pot slurry‐phase process. Unprecedented selectivities (>50 wt %) to C₂₊ alcohols are achieved at CO conversion levels >70 %, alongside negligible CO₂ side‐production. The efficient overall transformation is enabled by catalyst engineering, bridging gaps in operation temperature and intrinsic selectivity which have classically precluded integration of these reactions in a single conversion step. Swift capture of 1‐olefin Fischer–Tropsch primary products by the molecular hydroformylation catalyst, presumably within the pores of the solid catalyst is key for high alcohol selectivity. The results underscore that controlled cooperation between solid aggregate and soluble molecular metal catalysts, which pertain to traditionally dichotomic realms of heterogeneous and homogeneous catalysis, is a promising blueprint toward selective conversion processes.

Direct synthesis of higher alcohols from syngas over modified Mo2C catalysts under mild reaction conditions

The RhK/Mo2C catalyst exhibited remarkable selectivity for higher alcohols synthesis from syngas under mild reaction conditions owing to the interface sites between Rh and Mo2C promoted by K, which greatly facilitated CO insertion.

Moderate Surface Segregation Promotes Selective Ethanol Production in CO2 Hydrogenation Reaction over CoCu Catalysts

Cobalt-copper (CoCu) catalysts have industrial potential in CO/CO₂ hydrogenation reactions, and CoCu alloy has been elucidated as a major active phase during reactions. However, due to elemental surface segregation and dealloying phenomena, the actual surface morphology of CoCu alloy is still unclear. Combining theory and experiment, the dual effect of surface segregation and varied CO coverage over the CoCu(111) surface on the reactivity in CO₂ hydrogenation reactions is explored. The relationship between C-O bond scission and further hydrogenation of intermediate *CH₂ O was discovered to be a key step to promote ethanol production. The theoretical investigation suggests that moderate Co segregation provides a suitable surface Co ensemble with lateral interactions of co-adsorbed *CO, leading to promoted selectivity to ethanol, in agreement with theory-inspired experiments.

Atom Probe Tomography Investigations of Ag Nanoparticles Embedded in Pulse-Electrodeposited Ni Films

Atomic mapping of nanomaterials, in particular nanoparticles, using atom probe tomography (APT) is of great interest, as their properties strongly depend on shape, size, and composition. However, APT analyses of nanoparticles are extremely challenging, and there is an urgent need for developing robust and universally applicable sample preparation methods. Herein, we explored a method based on pulse electrodeposition to embed Ag nanoparticles in a Ni matrix and prepare APT specimens from the resulting composite film. By systematically varying the duty cycle during pulse electrodeposition, the dispersion and number density of the nanoparticles within the matrix was significantly enhanced as compared to DC electrodeposition. Several Ag nanoparticles were analyzed with APT from such samples. Shape distortions and biased compositions were observed for the Ag nanoparticles after applying a standard data reconstruction protocol. Numerical simulations of the field evaporation process showed that such artifacts were caused by a difference in the evaporation field of Ni and Ag and a local magnification effect. We expect such detrimental effects to be mitigated by a careful selection of the matrix material, matching the evaporation field of the nanoparticles. Furthermore, we anticipate that the method presented herein can be extended to a wider range of nanomaterials.

Atom Probe Analysis of Nanoparticles Through Pick and Coat Sample Preparation

The ability to analyze nanoparticles in the atom probe has often been limited by the complexity of the sample preparation. In this work, we present a method to lift–out single nanoparticles in the scanning electron microscope. First, nanoparticles are dispersed on a lacey carbon grid, then positioned on a sharp substrate tip and coated on all sides with a metallic matrix by physical vapor deposition. Compositional and structural insights are provided for spherical gold nanoparticles and a segregation of silver and copper in silver copper oxide nanorods is shown in 3D atom maps. Using the standard atom probe reconstruction algorithm, data quality is limited by typical standard reconstruction artifacts for heterogeneous specimens (trajectory aberrations) and the choice of suitable coatings for the particles. This approach can be applied to various unsupported free-standing nanoparticles, enables preselection of particles via correlative techniques, and reliably produces well-defined structured samples. The only prerequisite is that the nanoparticles must be large enough to be manipulated, which was done for sizes down to ~50 nm.

Toward alcohol synthesis from CO hydrogenation on Cu(111)-supported MoS2 - predictions from DFT+KMC

In the quest for cheap and efficient catalysts for alcohol synthesis from syngas, a material of interest is single-layer MoS₂ owing to its low cost, abundancy, and flexible structure. Because of the inertness of its basal plane, however, it is essential to find ways that make it catalytically active. Herein, by means of density functional theory based calculations of reaction pathways and activation energy barriers and accompanying kinetic Monte Carlo simulations, we show that while S vacancy row structures activate the MoS₂ basal plane, further enhancement of chemical activity and selectivity can be achieved by interfacing the MoS₂ layer with a metallic support. When defect-laden MoS₂ is grown on Cu(111), there is not only an increase in the active region (surface area of active sites) but also charge transfer from Cu to MoS₂, resulting in a shift of the Fermi level such that the frontier states (d orbitals of the exposed Mo atoms) appear close to it, making the MoS₂/Cu(111) system ready for catalytic activity. Our calculated thermodynamics of reaction pathways lead to the conclusion that the Cu(111) substrate promotes both methanol and ethanol as the products, while kinetic Monte Carlo simulations suggest a high selectivity toward the formation of ethanol.

Recent advances in the direct conversion of syngas to oxygenates

Direct synthesis of oxygenates from syngas is a promising way to utilize non-petroleum carbon resources because the oxygenate products serve as precursors for the downstream production of fuels and value-added chemicals.

Atom probe tomography

Atom probe tomography (APT) provides three-dimensional compositional mapping with sub-nanometre resolution. The sensitivity of APT is in the range of parts per million for all elements, including light elements such as hydrogen, carbon or lithium, enabling unique insights into the composition of performance-enhancing or lifetime-limiting microstructural features and making APT ideally suited to complement electron-based or X-ray-based microscopies and spectroscopies. Here, we provide an introductory overview of APT ranging from its inception as an evolution of field ion microscopy to the most recent developments in specimen preparation, including for nanomaterials. We touch on data reconstruction, analysis and various applications, including in the geosciences and the burgeoning biological sciences. We review the underpinnings of APT performance and discuss both strengths and limitations of APT, including how the community can improve on current shortcomings. Finally, we look forwards to true atomic-scale tomography with the ability to measure the isotopic identity and spatial coordinates of every atom in an ever wider range of materials through new specimen preparation routes, novel laser pulsing and detector technologies, and full interoperability with complementary microscopy techniques.

Nanoscale Perspectives of Metal Degradation via In Situ Atom Probe Tomography

We report a unique in situ instrument development effort dedicated to studying gas/solid interactions relevant to heterogeneous catalysis and early stages of oxidation of materials via atom probe tomography and microscopy (APM). An in situ reactor cell, similar in concept to other reports, has been developed to expose nanoscale volumes of material to reactive gas environments, in which temperature, pressure, and gas chemistry are well controlled. We demonstrate that the combination of this reactor cell with APM techniques can aid in building a better mechanistic understanding of resultant composition and surface and subsurface structure changes accompanying gas/surface reactions in metal and metal alloy systems through a series of case studies: O2/Rh, O2/Co, and O2/Zircaloy-4. In addition, the basis of a novel operando mode of analysis within an atom probe instrument is also reported. The work presented here supports the implementation of APM techniques dedicated to atomic to near-atomically resolved gas/surface interaction studies of materials broadly relevant to heterogeneous catalysis and oxidation.

Directional Gateway to Metal Oxidation: 3D Chemical Mapping Unfolds Oxygen Diffusional Pathways in Rhodium Nanoparticles

The interaction of oxygen with a reactive metal is ubiquitous, yet the precise atomic-level mechanisms and pathways leading to the formation of a surface oxide are not well-understood. We report oxygen atom distributions inside Rh single nanoparticles using atom probe microscopy (APM) and demonstrate that mainly facets of the ⟨022̅⟩ crystallographic directions act as oxygen-permeable gateways. The highly anisotropic spatial distribution of incorporated oxygen atoms is in agreement with video-field emission analyses according to which {113} facets of the ⟨022̅⟩ zones act as portals for subsurface diffusion. In addition to providing a more fundamental understanding of the precursor states to metal corrosion, in particular for the case of nanosized metal particles, our studies are also relevant for heterogeneous catalysis where catalytic activity and selectivity conform to reaction-induced structural changes of metal nanoparticles.

Interfacial Fe5C2-Cu catalysts toward low-pressure syngas conversion to long-chain alcohols

Long-chain alcohols synthesis (LAS, C₅₊OH) from syngas provides a promising route for the conversion of coal/biomass/natural gas into high-value chemicals. Cu-Fe binary catalysts, with the merits of cost effectiveness and high CO conversion, have attracted considerable attention. Here we report a nano-construct of a Fe₅C₂-Cu interfacial catalyst derived from Cu₄Fe₁Mg₄-layered double hydroxide (Cu₄Fe₁Mg₄-LDH) precursor, i.e., Fe₅C₂ clusters (~2 nm) are immobilized onto the surface of Cu nanoparticles (~25 nm). The interfacial catalyst exhibits a CO conversion of 53.2%, a selectivity of 14.8 mol% and a space time yield of 0.101 g g_cat⁻¹ h⁻¹ for long-chain alcohols, with a surprisingly benign reaction pressure of 1 MPa. This catalytic performance, to the best of our knowledge, is comparable to the optimal level of Cu-Fe catalysts operated at much higher pressure (normally above 3 MPa).

Long-chain alcohols synthesis from syngas conversion is a promising route for the production of high-value chemicals. Here the authors show that a heterogeneous Fe₅C₂/Cu catalyst derived from layered double hydroxides precursor exhibits excellent performance with a space time yield of 0.101 g g_cat⁻¹ h⁻¹ at a low pressure of 1 MPa.

Highly selective oxygen reduction to hydrogen peroxide on transition metal single atom coordination

Shifting electrochemical oxygen reduction towards 2e- pathway to hydrogen peroxide (H2O2), instead of the traditional 4e- to water, becomes increasingly important as a green method for H2O2 generation. Here, through a flexible control of oxygen reduction pathways on different transition metal single atom coordination in carbon nanotube, we discovered Fe-C-O as an efficient H2O2 catalyst, with an unprecedented onset of 0.822 V versus reversible hydrogen electrode in 0.1 M KOH to deliver 0.1 mA cm-2 H2O2 current, and a high H2O2 selectivity of above 95% in both alkaline and neutral pH. A wide range tuning of 2e-/4e- ORR pathways was achieved via different metal centers or neighboring metalloid coordination. Density functional theory calculations indicate that the Fe-C-O motifs, in a sharp contrast to the well-known Fe-C-N for 4e-, are responsible for the H2O2 pathway. This iron single atom catalyst demonstrated an effective water disinfection as a representative application.

Rate and selectivity hysteresis during the carbon monoxide hydrogenation over promoted Co/MnOx catalysts

While cobalt-based catalysts have been used in industrial Fischer-Tropsch synthesis for decades, little is known about how the dynamics of the Co-Co₂C phase transformation drive their performance. Here we report on the occurrence of hysteresis effects in the Fischer-Tropsch reaction over potassium promoted Co/MnO_x catalyst. Both the reaction rate and the selectivity to chain-lengthened paraffins and terminally functionalized products (aldehydes, alcohols, olefins) show bistability when varying the hydrogen/carbon monoxide partial pressures back and forth from overall reducing to carbidizing conditions. While the carbon monoxide conversion and the selectivity to functionalized products follow clockwise hysteresis, the selectivity to paraffins shows counter-clockwise behavior. In situ X-ray diffraction demonstrates the activity/selectivity bistability to be driven by a Co-Co₂C phase transformation. The conclusions are supported by High Resolution Transmission Electron Microscopy which identifies the Co-Co₂C transformation, Mn₅O₈ layered topologies at low H₂/CO partial pressure ratios, and MnO at high such ratios.

The question for the structure-reactivity relationship of cobalt-based catalysts for the carbon monoxide hydrogenation is as old as the reaction itself. Here the authors show kinetic hysteresis for a potassium-promoted cobalt-manganese oxide catalyst to be driven by the Co-Co₂C phase transition.

Atom Probe Tomography for Catalysis Applications: A Review

Atom probe tomography is a well-established analytical instrument for imaging the 3D structure and composition of materials with high mass resolution, sub-nanometer spatial resolution and ppm elemental sensitivity. Thanks to recent hardware developments in Atom Probe Tomography (APT), combined with progress on site-specific focused ion beam (FIB)-based sample preparation methods and improved data treatment software, complex materials can now be routinely investigated. From model samples to complex, usable porous structures, there is currently a growing interest in the analysis of catalytic materials. APT is able to probe the end state of atomic-scale processes, providing information needed to improve the synthesis of catalysts and to unravel structure/composition/reactivity relationships. This review focuses on the study of catalytic materials with increasing complexity (tip-sample, unsupported and supported nanoparticles, powders, self-supported catalysts and zeolites), as well as sample preparation methods developed to obtain suitable specimens for APT experiments.

Fabrication of Atom Probe Tomography Specimens from Nanoparticles Using a Fusible Bi-In-Sn Alloy as an Embedding Medium

We propose a new method for preparing atom probe tomography specimens from nanoparticles using a fusible bismuth-indium-tin alloy as an embedding medium. Iron nanoparticles synthesized by the sodium borohydride reduction method were chosen as a model system. The as-synthesized iron nanoparticles were embedded within the fusible alloy using focused ion beam milling and ion-milled to needle-shaped atom probe specimens under cryogenic conditions. An atom probe analysis revealed boron atoms in a detected iron nanoparticle, indicating that boron from the sodium borohydride reductant was incorporated into the nanoparticle during its synthesis.