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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Reductive catalytic fractionation of cotton stalks: catalytic strategy for tuning the selectivity of phenolic monomers

Pretreatment of lignocellulosic biomass is a primary step to delink lignin from the lignin-carbohydrate complex for bioethanol production and other value-added products. Presently, these processes yield lignin (technical) with significant structural changes compared to native lignin and make it difficult to valorize. Reductive catalytic fractionation (RCF) is an advanced pretreatment process to valorize native lignin to selective phenolic monomers before capitalizing on carbohydrates. Herein, cotton stalks (CS) were pretreated with ethanol: water mixture catalyzed by bimetallic, Ru-Ni/HY (RNY) and Ru-Fe/HY (RFY), and trimetallic, Ru-Fe-Ni/HY (RFNY), catalysts using the endogenously produced H 2 . The favorable catalytic properties of the RFNY catalyst, including high reducibility, acidity, metal dispersion, the synergistic effect of all the metals, and appropriate pore and particle size resulted in the highest catalytic activity. Maximum 92% delignification efficiency was achieved with 91% holocellulose retention. The extracted lignin after depolymerization in the same step produced a 19 wt.% yield of phenolic monomers. Increasing the duration of the reaction from 2 to 6 h increased the selectivity to saturated alkyl chain phenolics (1 to 16 wt.%) at the expense of hemicellulose (50 to 9%). The fate of carbohydrates left behind after the RCF (CS-RCF) process was analyzed through enzymatic saccharification and compared with raw CS and acid-pretreated CS. In conclusion, CS-RCF yielded maximum glucose yield (45 g/L) within an incubation period of 72 h.

09 BIOMASS FUELS↗
DOE OSTI2020

Nickel/gallium modified HZSM-5 for ethane aromatization: Influence of metal function on reactivity and stability

Bimetallic catalysts often outperform their monometallic counterparts due to the synergistic effect. Here we reported that the Ni/Ga co-functionalized HZSM-5 catalyst, specifically with Ni 1 /Ga 1 stoichiometric ratio, shows significantly improved selectivity (above 80 %) and stability than the Ni/HZSM-5 catalyst and higher activity (with identical selectivity) than the Ga/HZSM-5 catalyst in ethane aromatization. According to the transient experiment, the Ga and Ni 1 Ga 1 /HZSM-5 catalysts show an induction period of a few minutes. However, for Ni/HZSM-5 and Ni 1 Ga 1/3 /HZSM-5, the induction period increased to >10 min and >30 min, respectively, where up to 100 % of ethane was converted into methane and coke through cracking/hydrogenolysis. Furthermore, based on the generalized power-law equation model, a modified model for deactivation kinetic was proposed. Consequently, the influence of the metal function on the kinetic parameters was discussed. We anticipate the formation of Ni 3 Ga intermetallic alloy and its synergy with the exchanged Ga δ+ to be responsible for optimal BTX formation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

A mini review of cobalt-based nanocatalyst in Fischer-Tropsch synthesis

Fischer-Tropsch (F-T) synthesis, converting syngas to hydrocarbons, provides a green alternative for fuel production. Cobalt is one of the most intensively studied F-T catalysts due to its great activity, high stability, and relatively low cost. Overall, in this mini review, we summarized some recent advancements in the development of cobalt-based F-T catalysts focusing on the effects of particle size, surface oxidation states, crystallography, and bimetallic particles, with emphasis on the research from our group. Furthermore, non-steady state conditions were investigated to access the initial kinetics using chemical transient kinetics (CTK) experiments, which could bring more insights into the reaction mechanism and catalyst design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Tailoring olefin distribution via tuning rare earth metals in bifunctional Cu-RE/beta-zeolite catalysts for ethanol upgrading

Bioethanol to middle distillate technologies have offered a unique solution to produce renewable aviation fuel for decarbonizing the hard-to-electrify sectors. Here, we have developed the series of bimetallic Cu- and rare earth-containing (RE) Beta zeolite catalysts that yield high C 3+ alkene selectivity from ethanol upgrading (>80% selectivity at ~100% conversion, 623 K). The formation rates of butene isomers to C 5+ alkenes are linearly correlated with the strength of Lewis acidic RE identity, which follows the sequence of Yb 12 /Beta >Y 7 /Beta > Gd 12 /Beta > Ce 10 /Beta > La 12 /Beta. Rate measurements indicate that the RE selection plays the vital role in altering the rate of the key competitive reactions within the ethanol-to-alkenes reaction network, namely C 4 alcohol dehydration and C-C chain growth, which dictate alkene product distributions. Finally, these findings indicate a feasible and promising method for tailoring alkene product distributions from ethanol upgrading, which is of notable significance to the generation of renewable middle distillates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Role of Mg:Al ratio and Pt promotion on mitigating the deactivation of Ni-based methane steam reforming catalysts

Ni-based catalysts for CH 4 steam reforming require fine-tuning to withstand deactivation under dynamic operation conditions relevant to emerging H 2 -driven technologies. This study investigates the impact of the Mg:Al ratio and Pt presence in catalyst composition on the activity and stability of industrially relevant Ni-based mono- and bimetallic catalysts during simulated daily start-up and shut-down cycles in various gas atmospheres. The evolution of the catalyst structure during extensive testing procedures was investigated in detail by complementary electron microscopy, in situ/operando XAS and XRD. The results obtained revealed that catalyst deactivation is promoted at high Mg:Al ratios and especially affects the monometallic catalysts. By converting CH 4 at lower temperatures, Pt regulates the extent of Ni oxidation and its incorporation into MgO lattice. Further prevention of catalyst deactivation was achieved by optimizing the reactor shut-down procedure to minimize the simultaneous exposure to high temperatures and H 2 O vapors. By flushing the reactor with N 2 only around the reaction extinction temperature, a fraction of Ni species is maintained in metallic state, which is beneficial for the long-term activity and reaction operation economy.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Cu-induced robust Ni 2+ /Ni 3+ transition on amorphous Ni hydroxide-based electrocatalysts for advancing electrochemical ammonia oxidation and hydrogen evolution

The electrochemical ammonia oxidation reaction (AOR) is a promising anodic reaction for hydrogen production, offering a lower theoretical potential compared to oxygen evolution reaction. Despite this thermodynamic advantage, AOR suffers from sluggish multi-electron transfer reaction kinetics and the regeneration of catalytically active Ni 3+ species, which limits both activity and durability. In this study, amorphous NiCu bimetallic catalysts were prepared via facile precipitating metal nitrate deposition (PMND) method. The addition of Cu induces a robust Ni 2+ /Ni 3+ transition, stabilizing catalytically active Ni 3+ species and modulating the electronic structure of Ni. It alters the oxidation and desorption behavior of nitrogen-containing intermediates and facilitating their conversions to NO x species, resulting in fast active site regeneration. Furthermore, amorphous structure provides abundant dangling bonds, which enhances the intrinsic reactivity and accessibility of active sites rather than increasing the number of active sites. As a result, these effects accelerate the overall reaction kinetics. The optimized NiCu 5:1 catalyst achieved an ammonia removal efficiency of ∼100 % and a hydrogen production rate of 2.45 mmol/(h∙cm 2 ) at 1.6 V RHE .

Amorphous electrocatalyst↗
DOE OSTI2023

Oxidative ethane dehydrogenation under thermal vs. microwave heating over Ga/ZSM-5 and GaPt/ZSM-5

Conventional thermal heating versus microwave heating for the oxidative dehydrogenation of ethane with CO 2 as the oxidative co-reactant over 2%Ga/ZSM-5 and 1.5%Ga0.5%Pt/ZSM-5. The Ga/ZSM-5 and GaPt/ZSM-5 had a similar ethane conversion under microwave heating at 450 °C, compared to the thermally heated catalyst at 650 °C. The bimetallic GaPt/ZSM-5 performed better than the Ga/ZSM-5. Both the GaPtMWFB-450 °C and GaMWFB-450 °C resulted in a lower production rate to carbon monoxide and water than the TFB-650 °C, suggesting that the microwave heating is less favorable to the water gas shift reaction. In this study, microwave heating increased the catalytic conversion of ethane and selectivity to ethylene.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Microwave catalytic conversion of acetylene for co-production of hydrogen and carbon nanotubes

Natural gas conversion to hydrogen and solid carbon can drastically reduce the carbon footprint. Microwave plasma pyrolysis is an emerging process for chemical industries to directly convert methane (CH 4 ), the major component of natural gas, to hydrogen and carbon, which offers benefits such as fast process dynamics, flexibility, and high product yield. However, the formation of unwanted by-products, like acetylene (C 2 H 2 ), will require extra cost for gas separation. Plasma pyrolysis of CH 4 produces large amount of acetylene at downstream, which is currently used mainly for welding. Here, to avoid gas separation and upgrade acetylene from the downstream of methane plasma reactor, a novel approach toward its transformation to carbon nanotubes (CNT) and pure hydrogen (H 2 ) over Ni-based bimetallic catalyst driven by microwave irradiation has been reported in this work. The dominant gas product was hydrogen. Low concentrations of methane, ethane, and ethylene were observed in the product stream. Catalytic acetylene decomposition was carried out at 400 °C over Al 2 O 3 supported Ni catalyst. The results showed that, at 400 °C, acetylene was dehydrogenated to CNT and hydrogen was the dominant gas in product stream over 10Ni-1Pd-Al 2 O 3 catalyst. Characterizations of spent catalysts was conducted using Raman spectroscopy and transmission electron microscopy (TEM) to investigate the properties of carbon deposited over the catalyst during the catalytic acetylene decomposition. The results highlight that methane can be efficiently converted to hydrogen and CNT through 2-step process, microwave plasma and microwave catalytic conversion of intermediate acetylene, operated in a single reactor system driven by microwave.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Fine-tuning catalytic selectivity by modulating catalyst-environment interactions: CO 2 hydrogenation over Pd-based catalysts

Capturing catalytic behaviors under operational conditions is pivotal to gaining a mechanistic understanding and promoting the design of robust catalysts. The challenge lies in the difficulty of monitoring real-time surface dynamics driven by catalyst-environment interactions. Here, in this work, we introduce a framework based on density functional calculations and kinetic modeling. This framework significantly improves the accuracy of theoretical models’ descriptions of experimental observations by quantifying environmental impacts on surface phases and active sites. CO 2 hydrogenation over Pd-based catalysts is taken as a showcase. The observed selectivity variations of Pd and Pd-M bimetallic catalysts strongly correlate with hydrogen coverage maintained under typical CO 2 hydrogenation conditions. By reducing the amount of surface hydrogen, the selectivity tuned effectively from formic acid toward CO and methanol. This study not only deepens the comprehension of dynamics of active sites under active chemical conditions but also introduces an alternative opportunity for catalytic tuning by modulating catalyst-environment interactions.

03 NATURAL GAS↗
DOE OSTI2022

Heterogeneous hydroformylation of alkenes by Rh-based catalysts

Heterogeneously catalyzed hydroformylation reactions avert the problems of separation in homogeneous reactions, reduce the discharge of phosphorus-containing wastes, and prevent the loss of precious metals. This review summarizes the developments of catalysts for heterogeneous hydroformylation in the last decade and proposes potential modification methods for future improvements. The hydroformylation properties of different reactants are compared in order to emphasize the fact that various olefins face unique challenges. The hydroformylation of ethylene requires the enhancement of catalytic activity and chemoselectivity, whereas that of propylene needs improvements in both chemoselectivity and regioselectivity. The hydroformylation of longer-chain olefins and styrene seeks further improvement in regioselectivity. The catalytic properties of activity, selectivity, and stability can be tuned through electronic effects (bimetallic effects, phosphine ligands, and single-atom catalysts), steric hindrance (encapsulation structures, diphosphine ligands, and local functional groups), and reaction condition optimization (temperature, pressure, and solvents). Furthermore, the understanding of these effects is critical in future catalyst design for heterogeneous hydroformylation reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Recent developments in Pt–Co catalysts for proton-exchange membrane fuel cells

Development of Pt-based oxygen reduction reaction catalysts with high efficiency and high durability is central to the application of proton-exchange membrane fuel cell systems. Pt–Co bimetallic catalysts have drawn extensive attention owing to their capability of delivering high performance and long lifetime for fuel cell applications including light-duty and heavy-duty vehicles. However, further improvements in durability and performance are needed to meet market requirements. To fully exploit the potential of Pt–Co catalysts, new insights into the relationship between catalyst properties and fuel cell performance and durability are needed, and more effective methods to tailor the features of Pt–Co catalysts need to be developed. This review provides a summary and perspective on recent efforts, including work on customizing the Pt shell and Pt:Co ratio, tailoring the crystal structure, and improving carbon support properties, with a particular emphasis on mechanisms leading to enhancement of mass activity, power density, and durability in membrane electrode assembly testing.

25 ENERGY STORAGE↗
DOE OSTI2025

Quantifying the effects of artificial aging on the ignition and self-propagating reactions of Ni(V)/Al multilayers

Bimetallic, reactive multilayers are uniformly structured materials composed of alternating nanoscale layers that may be ignited to produce self-propagating intermetallic-formation reactions. When reactive multilayers age, there is a change in local composition and loss of stored chemical energy due to mass transport and rearrangement at the interfaces. Here, to quantify the long-term reliability of commercial Ni(V)/Al multilayers, the effects of accelerated aging on both ignition sensitivity and self-propagating reactions have been examined. Thermally aged samples were characterized using transmission electron microscopy, differential scanning calorimetry, and laser ignition combined with high-speed videography. The analytically quantifiable nature of both continuous wave laser ignition and reactive wave propagation enabled calculations of Arrhenius rate constants for as-received and various heat-treated multilayers. With heat treatment, there is a change in the intermixed thickness and interfacial chemistry that decreases the activation energy for point ignition but increases it for self-propagating reactions. This finding implies that with increased thermal aging, the reaction becomes easier to facilitate in the solid state but harder in the liquid phase.

Energetic material↗
DOE OSTI2022

Density functional theory study of formation and diffusion of hydrogen, deuterium, and tritium in Pd-V intermetallic compounds

Permeation of hydrogen isotopes in palladium/vanadium bimetallic membranes is known to deteriorate over time because of Pd-V interdiffusion. Additionally, intermetallic compounds may form in the interdiffusion region. Density functional theory is employed to study how Pd-V compounds may affect the permeation. Three compounds Pd 8 V, alpha-Pd 2 V, and PdV 4 are explored in this study. Formation and migration energies of hydrogen, deuterium, and tritium are calculated and subsequently compared to the data in pure Pd and V metals. The calculations show that both the formation and migration energies in the compounds are higher than in the pure metals. Thus, the permeation of these isotopes in the compounds is lower than in the pure metals. In addition, the least permeable compound is the one near the middle of the composition range, i.e. the alpha-Pd 2 V. The results provide atomistic insight for the permeation reduction in Pd/V membranes as interdiffusion progresses.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Plasma catalytic non-oxidative methane conversion to hydrogen and value-added hydrocarbons on zeolite 13X

Non-thermal plasma has unfolded highly efficient, safe to operate novel routes for methane conversion to hydrogen. In this work, methane conversion is performed under atmospheric dielectric barrier discharge (DBD) plasma with and without 13X zeolite-based catalysts i.e., 13X, Ga/13X, Pd/13X, and Pd-Ga/13X. Experimental results indicate that the plasma catalytic process delivered almost twofold higher product yield than the plasma only route. The binary Pd-Ga catalyst possesses highest catalytic performance with about 40 % CH 4 conversion at an input flowrate of 5 cm 3 min -1 and 2W due to the formation of the Pd-Ga alloy, which acts as catalytic active centre for activating C–H bonds. Product yield can be tailored by the catalyst design where the bimetallic Pd-Ga/13X preferably favours the hydrocarbon formation while H 2 is the dominant product obtained over the Pd/13X. The cleavage of C–H bonds of methane molecule over the plasma only route is mainly governed by energetic electrons in the gaseous phase the catalyst activity, and plasma-catalyst synergism play a significant role in the plasma catalysis process. Further, the findings from this work provide significant insights into the methane activation for subsequent optimization of the methane conversion processes operated on floating production, storage, and offloading vessels (FPSOVs). Exploiting untapped offshore natural gas reserves, where conventional pipeline systems are less economical.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

BiCuI 4 (Pyridine) 5 a neutral ligand-supported compound of BiI 3 and CuI

Reaction of equimolar pyridine (Py) solutions BiI 3 and CuI produces the Py-supported 1:1 bimetallic complex BiCuI 4 (Py) 5 in quantitative yield. The title complex is only the second neutral complex to feature Cu–I–Bi bridging and shows an octahedral trans-[BiI 4 (Py) 2 ] unit joined to a distorted tetrahedral CuI(Py) 3 unit by an iodide bridge. The complex shows low thermal stability, decomposing under modest heating or vacuum to produce a mixture of BiI 3 and CuI. Thus, it is a potential entry/precursor to BiI 3 /CuI chemistry. Natural Localized Molecular Orbital (NLMO) calculations were performed to analyze the nature of the Cu–I–Bi bonds, revealing that the title compound lies on the cusp of being [Cu(Py) 3 ] + [BiI 4 (Py) 2 ] – . Diffuse reflectance spectroscopy measurements show a strong absorption band with an optical bandgap energy of 1.94 eV. Theoretical density of states (DOS) and time-dependent density functional theory (TD-DFT) experiments to map the electronic structure assign the primary electronic transition as a mixed halide/metal-to-ligand charge transfer between Cu–I–Bi donor orbitals and Py π* acceptor orbitals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Pd and octahedra do not get along: Square planar [PdS 4 ] units in non-centrosymmetric La 6 PdSi 2 S 14

Non-linear optical (NLO) materials require a balance of high second-harmonic generation (SHG) signal and laser damage threshold (LDT), as well as phase matchable behavior. Herein, we report a new member of the (RE) 6 (TM) x (Tt) 2 Q 14 family of compounds, La 6 PdSi 2 S 14 , which, unlike all other reported TM analogues crystallizing in hexagonal P6 3 space group, crystallizes in the non-centrosymmetric monoclinic P2 1 space group. The crystal structure contains chains of edge-sharing distorted square planar [PdS 4 ] units. The square-planar coordination of Pd in La 6 PdSi 2 S 14 exhibits remarkable NLO properties with high SHG (3.7 × AgGaS 2 ) and LDT (3 × AgGaS 2 ) values as well as phase matchability. This shows the promise of novel materials with distorted structural motifs for enhanced NLO properties. Further, upon formation of bimetallic chiral sulfides containing both Cu and Pd, Cu occupies the opposite faces of the octahedra forming [CuS 3 ] units while Pd can be stabilized in the center of PdS 6 octahedra in the hexagonal P6 3 crystal structure of La 6 Pd 0.5 CuSi 2 S 14 . This suggests that it is possible to form mixed metal systems which could further enhance NLO properties by incorporation of additional structural distortions.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Evolution of steady-state material properties during catalysis: Oxidative coupling of methanol over nanoporous Ag 0.03 Au 0.97

Activating pretreatments are used to tune surface composition and structure of bimetallic-alloy catalysts. Herein, the activation-induced changes in material properties of a nanoporous Ag 0.03 Au 0.97 alloy and their subsequent evolution under steady-state CH 3 OH oxidation conditions are investigated. Activation using O 3 results in AgO and Au 2 O 3 , strongly enriching the near-surface region in Ag. These oxides reduce in the O 2 /CH 3 OH mixture, yielding CO 2 and producing a highly Ag-enriched surface alloy. At the reaction tem-perature (423 K), Ag realloys gradually with Au but remains enriched (stabilized by surface O) in the top few nanometers, producing methyl formate selectively without significant deactivation. At higher tem-peratures, bulk diffusion induces sintering and Ag redistribution, leading to a loss of activity. These find-ings demonstrate that material properties determining catalytic activity are dynamic and that metastable (kinetically trapped) forms of the material may be responsible for catalysis, providing guiding principles concerning the activation of heterogeneous catalysts for selective oxidation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Enhanced alcohol production over binary Mo/Co carbide catalysts in syngas conversion

Recently metal carbide catalysts have attracted attention as alternatives to pure metals for the conversion of syngas to higher oxygenates, a process which could enable the sustainable production of fuels, polymers, and chemicals. Although Mo and Co carbides have both shown promise for higher oxygenate production, they have not achieved the requisite activity and selectivity for practical implementation. In this work we synthesize and characterize a binary Mo and Co carbide catalyst that exhibits improved activity and oxygenate selectivity relative to either pure metal carbide. In this work, we apply a combination of advanced electron microscopy and X-ray diffraction to show that the binary Mo/Co carbide catalyst forms uniformly mixed amorphous nanoparticles. Through in situ X-ray absorption spectroscopy studies, we determine that the structure of the mixed metal carbide catalyst under reaction conditions consists of both carbidic and bimetallic components. By testing the catalytic properties of a series of Mo/Co carbide catalysts prepared by different synthesis methods, we find that the Mo and Co sites must be in close contact to achieve improved syngas conversion to higher alcohols. Through in situ DRIFTS measurements, both Mo and Co atoms at the surface of the catalyst are identified as adsorption sites for reactive species.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗