Assessing the viability of K-Mo2C for reverse water-gas shift scale-up: molecular to laboratory to pilot scale
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99 GENERAL AND MISCELLANEOUS↗
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Determining the Role of Synthesis and Reaction Conditions on the Exposed Surface and Shape of ..beta..-Mo2C Catalysts
The production of drop-in quality biofuels typically can be achieved through catalytic fast pyrolysis (CFP) of biomass, followed by hydrodeoxygenation (HDO) of the vapor-phase product to reduce the oxygen content and stabilize the bio-oil product. To favor selectivity toward desired deoxygenation products, bifunctional catalysts with both acidic and hydrogenation sites are often employed. Due to both its oxophilicity and its ability to promote hydrogenation reactions, molybdenum carbide catalysts have shown promise for promoting the HDO of CFP vapors. However, the surface structure and composition of carbide catalyst particles are not well understood, precluding the establishment of fundamental structure-function relationships needed for the rational development of molybdedum carbide for HDO, as well as other reactions. For orthorhombic ..beta..-Mo2C, the (100) facet is largely studied for computational surface-reaction analyses, possibly due to its similarities with the close-packed (111) facet of noble-metal catalysts. However, it has previously been postulated through ab initio thermodynamic studies that the (111), (110), and (011) facets are most stable, though there is no consensus. Furthermore, while a majority of previous surface stability analyses of ..beta..-Mo2C focus on bulk terminations, the highly carburizing synthesis conditions and the use of ..beta..-Mo2C in carbon-containing reaction applications could introduce non-stoichiometric coverages of surface carbon. As such, this study uses ab initio thermodynamics calculations to assess the relative surface stability of the low-index facets of ..beta..-Mo2C, including consideration of varying the coverage of surface carbon. From this information, Wulff constructions are utilized to predict the synthesis and reaction condition-dependent shape and surface carbon composition of ..beta..-Mo2C catalyst particles.
BIOMASS FUELS,INORGANIC, ORGANIC, PHYSICAL, AND AN↗
Accelerating Catalyst Development for Biofuel Production through Multiscale Catalytic Fast Pyrolysis of Biomass over Mo2C
Advanced catalytic materials play an enabling role in producing renewable fuels and chemicals from biomass, thereby helping meet the global climate-change goals set forth by the Intergovernmental Panel on Climate Change. Herein, we present a multiscale approach to accelerate the catalyst-process development cycle for catalytic fast pyrolysis (CFP) of biomass over Mo2C. Mo2C has been shown to possess co-localized acidic and metallic sites and exhibit high activity for deoxygenation of biomass pyrolysis model compounds. However, critical knowledge gaps remain regarding the effectiveness of this catalyst for CFP of whole biomass. We address these knowledge gaps and demonstrate that Mo2C is effective at deoxygenating biomass-pyrolysis products in the presence of H2 but that it undergoes rapid selective and non-selective deactivation. The knowledge gaps addressed from this integrated study, targeting appropriate experiments across scales and feed types, enabled identification of critical modifications for advancing the CFP catalyst-process development cycle.
biofuels↗
In-Cu alloy substrates for low-temperature chemical vapor deposition of Mo2C
Two-dimensional transition metal carbides are promising materials because of their potential for combining the favorable properties of transition metal carbides with the high aspect ratio of two-dimensional materials. Though commonly produced by top-down wet-chemical synthesis methods, synthesis by chemical vapor deposition is being considered because of its ability to achieve large areas, controlled layer thickness, and reduced defect density. Typically, liquid Cu is used as a synthesis substrate, though the high melting temperature of Cu (1085 °C) requires high synthesis temperatures. Thus, alternative substrates have been studied in order to reduce the necessary melting temperature. This work systematically studies the impact of synthesis parameters and substrate composition on the growth of ultrathin Mo2C (∼4–120 nm thick) by chemical vapor deposition on an In-Cu alloy. Mo2C flake size increases, and graphene/Mo2C heterostructures form with an increase in the methane flow rates. Increasing the In composition slightly decreases surface coverage and coalescence but does not appreciably impact the Mo2C flake size. Increasing In content also decreases the alloy substrate melting temperature so that a lower temperature synthesis (800 °C) can be performed. However, the necessary high temperatures for pyrolysis of methane lead to a lower limit for the synthesis temperature, similar to graphene.
Young, Katherine T. (ORCID:0000000285845576)↗
Materials Data on Mo2C by Materials Project
Mo2C is Molybdenite-like structured and crystallizes in the hexagonal P-6m2 space group. The structure is two-dimensional and consists of one Mo2C sheet oriented in the (0, 0, 1) direction. Mo2+ is bonded in a distorted T-shaped geometry to three equivalent C4- atoms. All Mo–C bond lengths are 2.17 Å. C4- is bonded to six equivalent Mo2+ atoms to form distorted edge-sharing CMo6 pentagonal pyramids.
36 MATERIALS SCIENCE↗
Materials Data on Mo2C by Materials Project
Mo2C is beta Vanadium nitride-like structured and crystallizes in the orthorhombic Pbcn space group. The structure is three-dimensional. Mo2+ is bonded in a distorted T-shaped geometry to three equivalent C4- atoms. There are a spread of Mo–C bond distances ranging from 2.11–2.14 Å. C4- is bonded to six equivalent Mo2+ atoms to form a mixture of corner and edge-sharing CMo6 octahedra. The corner-sharing octahedra tilt angles range from 49–50°.
36 MATERIALS SCIENCE↗
Understanding the effect of Mo2C support on the activity of Cu for the hydrodeoxygenation of glycerol
Not Available
You, Kyung-Eun↗
Biomass Ex-Situ CFP Catalyst Design: A Mo2C Case Study to Evaluate if Trends in Model Compound Reactivity Translate to Real Biomass Feeds
Pyrolysis of biomass generates hundreds of molecules with different functional groups; water, char and inorganics are also produced. In general, new catalysts are evaluated with single model compounds.
biofuels↗
2D-EFICACY: Control of Metastable 2D Carbide[1]Chalcogenide Heterolayers: Strain and Moire Engineering
The experimental isolation of graphene led to the discovery of an entirely new world of two-dimensional (2D) materials in which the 2D nature often leads to emergent behaviors not seen in bulk systems. 2D transition metal dichalcogenides (TMDs) exhibit physico-chemical properties that depend on the transition metal, polymorph, thickness, and presence and type of defects. Recently, a group of thin (10-100nm) transition metal carbides (TMCs), such as Mo2C, has been synthesized that exhibit a thickness-dependent superconducting critical temperature (Tc). These thin TMCs are different from MXenes, another class of 2D materials consisting of few layers of nitrides or carbides (<5nm) produced by chemical etching and delamination. The goal of this renewal proposal is to combine experiment and computation to synthesize and elucidate the guiding principles that control the growth, orientation and strain of heterostacks of thin TMCs and TMDs composed with Nb, Ti and W. We expect to stabilize metastable hybrid phases of TMCs sandwiched between TMDs (H-TMD/Cs) with unprecedented physico-chemical properties. As part of previous DOE-funded work by the Terrones/Sinnott groups, thin (10-100 nm thick) Mo2C flakes were successfully synthesized by chemical vapor deposition (CVD). By subsequently exposing Mo2C to H2S, partial chalcogenization was achieved, resulting in heterostacks of MoCx phases and MoS2. The formation of MoS2 led to a deficiency of Mo atoms in the underlying Mo2C, resulting in an inhomogeneous phase change from α-Mo2C to γ’-MoCx and then to γ-MoC. The γ’-MoCx is a strained metastable phase and the heterostack of all three phases demonstrated an increased Tc relative to that of α-Mo2C, from 4 to 6K; its interleaved layered structure consisting of superconducting and semiconducting phases is ideal for future studies of Josephson junction series arrays. Moiré patterns in these heterostacked systems could result in new phenomena, as moiré patterns in bilayer graphene showed unconventional superconductivity and moiré excitons have been observed in twisted TMD heterobilayers. The scientific hypothesis of the proposed synergistic computational and experimental research is that orientation and strain control within confined thin metastable TMCs, sandwiched by stable phases of TMCs and layered TMDs, will depend on kinetic and thermodynamic “knobs” that include fast temperature changes, chalcogen diffusion through preferred crystallographic planes, reaction times, pressure, reactive atmosphere, precursors, and surfactants, which will also tailor properties such as superconductivity, magnetism, ferroelectricity, piezoelectricity, and catalytic performance. We will develop the guiding principles for the synthesis and stabilization of metastable H-TMD/Cs based on Nb, Ti and W. In order to validate the hypothesis, four tasks are proposed: The first task will synthesize ultra-thin TMCs based on Nb, W and Ti, by: 1) adapting the CVD method used for Mo2C, 2) plasma assisted CVD, 3) defect-mediated CVD processes, and 4) cryo-milling of carbide powders. The second task will accomplish the synthesis and basic physico-chemical characterizations of H-TMD/Cs by chalcogenization of the materials synthesized in task one, and by carbonization of TMDs. H-TMD/Cs will also be investigated for their suitability in energy conversion applications such as supercapacitors, Li and multivalent ion batteries, and electrocatalysts, topics of interest to DoE. These tasks will be carried out in close conjunction with density functional theory (DFT) calculations with insights into energetics, lattice parameters, stability, phase diagrams, band structures, and density of states of H-TMD/Cs. The third task will characterize and evaluate strain and moiré patterns at the interfaces of different H-TMD/Cs by high-resolution scanning transmission electron microscopy (HR-STEM), scanning tunneling microscopy (STM), and conductive tip atomic force microscopy. Nudged elastic band calculations with DFT will be performed to understand the chalcogen diffusion process, which will provide insights into the interfaces between different phases of TMCs and TMDs. The fourth task aims at quantifying the stability and dynamics of H-TMD/Cs by in-situ TEM and Raman studies under heating, strain, and electrical biasing. Phonon calculations using DFT will provide a basis for interpreting Raman spectra. This coherent framework involving synthesis, characterization, and computation will result in a broad scientific impact for energy related applications. The ability to develop new H-TMD/Cs will enhance a range of applications that include batteries, catalysts, switches, sensors, quantum computing components and smart coatings.
2-Dimensional materials↗
Early-Stage Evaluation of Catalyst Manufacturing Cost and Environmental Impact Using CatCost
The costs and environmental impacts of catalyst manufacture are often neglected during early-stage research because of a lack of accessible, standardized tools to assess them. Here we report the key features of CatCost, a free and public estimation tool for the evaluation of catalyst cost. We demonstrate its functionality with a case study of diverse catalysts (ZSM-5, Pt/TiO2 and Mo2C) for the catalytic fast pyrolysis of biomass. We quantified the economic and environmental improvements made by replacing circulating-bed ZSM-5 with more stable, fixed-bed Pt/TiO2 and Mo2C catalysts, while revealing the effects of synthesis methods and production scale on catalyst costs. The manufacture of ZSM-5 had a large processing cost contribution that was strongly scale dependent, whereas the costs of the other catalysts were dominated by raw materials at all scales. Furthermore, while ZSM-5 costs the least per kilogram, the more stable catalysts cost half as much per gallon of fuel.
BIOMASS FUELS,ENERGY PLANNING, POLICY, AND ECONOMY↗
Materials Data on Mo3C2 by Materials Project
Mo3C2 crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one Mo2C sheet oriented in the (0, 0, 1) direction and one Mo4C3 sheet oriented in the (0, 0, 1) direction. In the Mo2C sheet, Mo+2.67+ is bonded in a distorted T-shaped geometry to three equivalent C4- atoms. All Mo–C bond lengths are 2.14 Å. C4- is bonded to six equivalent Mo+2.67+ atoms to form edge-sharing CMo6 octahedra. In the Mo4C3 sheet, there are two inequivalent Mo+2.67+ sites. In the first Mo+2.67+ site, Mo+2.67+ is bonded in a distorted T-shaped geometry to three equivalent C4- atoms. All Mo–C bond lengths are 2.07 Å. In the second Mo+2.67+ site, Mo+2.67+ is bonded to six C4- atoms to form a mixture of edge and corner-sharing MoC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (2.18 Å) and three longer (2.23 Å) Mo–C bond lengths. There are two inequivalent C4- sites. In the first C4- site, C4- is bonded to six equivalent Mo+2.67+ atoms to form a mixture of edge and corner-sharing CMo6 octahedra. The corner-sharing octahedral tilt angles are 2°. In the second C4- site, C4- is bonded to six Mo+2.67+ atoms to form a mixture of edge and corner-sharing CMo6 octahedra. The corner-sharing octahedral tilt angles are 2°.
36 MATERIALS SCIENCE↗
Scalable Synthesis of 2D Mo 2 C and Thickness‐Dependent Hydrogen Evolution on Its Basal Plane and Edges
Abstract 2D transition metal carbides (2D TMCs and MXenes) are promising candidates for applications of energy storage and catalysis. However, producing high‐quality, large 2D flakes of Mo2C MXene has been challenging. Here, a new salt‐assisted templating approach is reported that enables the direct synthesis of 2D Mo 2 C with low defect concentrations. KCl acts as a template to form an intermediate 2D product, facilitating Mo 2 C formation without coarsening upon melting. The thickness of the flakes produced can range from monolayer (0.36 nm) to 10 layers (4.55 nm), and the electrocatalytical hydrogen evolution reaction (HER) activity of 2D Mo 2 C is inversely proportional to its thickness. The monolayer Mo 2 C shows remarkable HER performance with a current density of ≈6800 mA cm − 2 at 470 mV versus reversible hydrogen electrode and an ultrahigh turnover frequency of ≈17 500 s − 1 . This salt‐assisted synthesis approach can also produce WC and V 8 C 7 nanosheets, expanding the family of 2D carbides. The new pathway eliminates the need for layered ceramic precursors, making it a versatile approach to direct synthesis of MXene‐like 2D carbides.
Chemistry↗
Assessing the role of surface carbon on the surface stability and reactivity of β-Mo 2 C catalysts
Transition-metal carbides, e.g., Mo 2 C, promote industrially important catalytic reactions with activities comparable to precious-metal catalysts. Yet, the nature of the catalytically active sites remains unclear. Herein, density functional theory calculations are applied to systematically assess the stability of low-Miller index facets of β-Mo 2 C as a function of carbon chemical potential (uC) and surface-carbon coverage (nC). When reconstruction of surface carbon is considered to characterize β-Mo 2 C under varying environments, the (111) and (101) surfaces are predicted to be most stable, dominating the Wulff particle surface area across a broad range of uC. The surface-carbon coverage is predicted to steadily increase for all low-index facets under more carburizing reaction conditions, leading to distinct effects on the adsorption energetics for atomic hydrogen and oxygen. Whereas H binding is only slightly affected by surface carbon, O is systematically destabilized. The findings reported indicate that consideration of only bulk-terminated surfaces, and the common focus of theoretical studies on the bulk-truncated, close-packed (100) surface, is likely insufficient to capture the reactivity of the working ..beta..-Mo 2 C catalyst. Similar to metal oxides, β-Mo2C catalysts are predicted to be dynamic materials with surface compositions and reactivities that evolve in response to the environment.
36 MATERIALS SCIENCE↗
The Development of Catalysts for Upgrading of Pyrolysis Vapor for Refinery Feedstocks and Intermediates (CRADA Final Report)
Catalytic fast pyrolysis (CFP) is a versatile technology platform to convert biomass into fungible hydrocarbon transportation fuels and chemical co-products. Key technical barriers to reaching this goal include increasing the product yields and achieving the desired fuel properties for gasoline, diesel, and jet range fuels or blendstocks that would be suitable for introduction into existing refinery unit operations. Overcoming these barriers will require durable catalysts that are effective at upgrading and stabilizing biomass pyrolysis vapors. Towards these goals, this CRADA leveraged NREL experience as a leader in biomass pyrolysis research and Johnson Matthey's (JM) experience as a leader in the production of advanced catalytic materials. The scope spanned CFP catalyst development, characterization, multi-scale reaction testing, and computational modeling. CRADA benefits to DOE, Participant, and U.S. Taxpayer: Assists laboratory in achieving programmatic scope, Uses the laboratory’s core competencies. The purpose of this CRADA was to develop and deploy catalysts for biomass CFP to help achieve cost-competitive biofuels and bio-based products. This was accomplished through a close collaboration between biomass conversion researchers at NREL and catalyst development researchers at JM. Summary of Research Results: Focus Area 1. Foundational research on catalytic conversion and deactivation: Key interactions between pyrolysis vapors and heterogeneous catalysts were probed through catalyst characterization, model compound reaction testing, and atomistic-scale computational modeling. Catalyst development focused on multifunctional materials, which include zeolites, oxides, carbides, and nitrides. Computational modeling identified reaction mechanisms and elucidated surface chemistry to test hypotheses regarding mechanisms of deoxygenation, coupling, cracking, dehydration, coke formation, hydrogen transfer, and aromatic ring reactions. This information was used to design multifunctional catalysts to increase product yields, control product selectivity, and reduce deactivation during CFP and downstream processing steps. The results served to increase fundamental understanding of key catalyst attributes and durability features for the upgrading of biomass pyrolysis vapors. Model compound experiments confirmed the importance of metal-acid bifunctionality for the deoxygenation of lignin-derived phenolic species under hydrodeoxygenation conditions. This insight led to the development of catalysts such as Pt/TiO2 and Mo2C, which were confirmed as high-performing materials during subsequent bench-scale experiments using biomass-derived pyrolysis vapors. This focus area also led to the identification of important catalyst deactivation mechanisms associated with the deposition of inorganic contaminants such as potassium. The molecular-level insight from model compound experiments and computational modeling, shown in Figure 1, informed the development of regeneration procedures that have been shown to be effective for restoration of > 90% of initial catalyst activity. This understanding has subsequently been translated to other catalyst systems, including zeolite materials that can be operated without requirements for co-fed hydrogen.
09 BIOMASS FUELS↗