Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “catalyst”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,639 records · Page 91
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Temperature-programmed deoxygenation of acetic acid on molybdenum carbide catalysts

Temperature programmed reaction (TPRxn) is a simple yet powerful tool for screening solid catalyst performance at a variety of conditions. A TPRxn system includes a reactor, furnace, gas and vapor sources, flow control, instrumentation to quantify reaction products (e.g., gas chromatograph), and instrumentation to monitor the reaction in real time (e.g., mass spectrometer). Here, we apply the TPRxn methodology to study molybdenum carbide catalysts for the deoxygenation of acetic acid, an important reaction among many in the upgrading/stabilization of biomass pyrolysis vapors. TPRxn is used to evaluate catalyst activity and selectivity and to test hypothetical reaction pathways (e.g., decarbonylation, ketonization, and hydrogenation). Furthermore, the results of the TPRxn study of acetic acid deoxygenation show that molybdenum carbide is an active catalyst for this reaction at temperatures above ca. 300 °C and that the reaction favors deoxygenation (i.e., C-O bond-breaking) products at temperatures below ca. 400 °C and decarbonylation (i.e., C-C bond-breaking) products at temperatures above ca. 400 °C.

09 BIOMASS FUELS↗
NASA NTRS2015

Evaluation of Low Temperature CO Removal Catalysts

CO removal from spacecraft gas streams was evaluated for three commercial, low temperature oxidation catalysts: Carulite 300, Sofnocat 423, and Hamilton Sundstrand Pt1. The catalysts were challenged with CO concentrations (1-100 ppm) under dry and wet (50% humidity) conditions using 2-3 % O2. CO removal and CO2 concentration were measured at constant feed composition using a FTIR. Water vapor affected the CO conversion of each catalyst differently. An initial screening found that Caulite 300 could not operate in humid conditions. The presence of water vapor affected CO conversion of Sofnocat 423 for challenge concentrations below 40 ppm. The conversion of CO by Sofnocat 423 was 80% at CO concentrations greater than 40 ppm under both dry and moist conditions. The HS Pt1 catalyst exhibited CO conversion levels of 100% under both dry and moist conditions.

Low Temperature↗
NASA NTRS2016

Synthesis and Characterization of Cobalt Containing Nanoparticles on Alumina A Potential Catalyst for Gas to Liquid Fuels Production

Fisher-Tröpsch synthesis (FTS) is a century-old gas-to-liquid (GTL) technology that commonly employs cobalt (Co, on an oxide support) or iron (supported or not) species catalysts. It has been well established that the activity of the Co catalyst depends directly upon the number of surface Co atoms. The addition of promoter (mainly noble) metals has been widely utilized to increase the fraction of Co that is available for surface catalysis. Direct synthesis of Co nanoparticles is a possible alternative approach; our preliminary synthesis and characterization efforts are described. Materials were characterized by various transmission microscopies and energy dispersive spectroscopy. Tri-n-octylphosphine oxide (TOPO) and dicobalt octacarbonyl were heated under argon to a temperature of 180 deg with constant stirring for 1 hr. Quenching the reaction in toluene produced Co-containing nanoparticles with a diameter of 5 to 10 nm. Alternatively, an alumina support (SBA-200 Al2O3) was added; the reaction was further stirred and the temperature was decreased to 140 deg to reduce the rate of further growth/ripening of the nucleated Co nanoparticles. A typical size of Co-containing NPs was also found to be in the range of 5 to 10 nm. This can be contrasted with a range of 50 to 200 nm for conventionally-produced Co-Al2O3 Fischer-Tröpsch catalysts. This method shows great potential for production of highly dispersed catalysts that are either supported or unsupported.

aluminum oxides↗
DOE OSTI2017

A Catalyst for Change

PNNL’s catalysis research is serving as a catalyst for changing how our nation will secure a strong, clean energy future. Senior Physical Chemist Johannes Lercher leads an award-winning team that is developing catalysts that efficiently make fuels from alternate feedstocks, such as biomass, and can store electrical energy in chemical bonds. The researchers are also creating catalysts that can increase vehicle fuel efficiency, while simultaneously cutting emissions. About 80 percent of all man-made materials — from plastics to pharmaceuticals — are made using catalysts. Through PNNL’s Institute for Integrated Catalysis, Johannes and colleagues study how to speed the catalysis reaction process for manufacturers, which ultimately cuts costs and production time.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2018

Beating Heterogeneity of Single-Site Catalysts: MgO-Supported Iridium Complexes

Catalysts consisting of isolated metal atoms on oxide supports have attracted wide attention because they offer unique catalytic properties, but their structures remain largely unknown because the metals are bonded at various, heterogeneous surface sites. Now, by using highly crystalline MgO as a support for metal sites made from a mononuclear organoiridium precursor and investigating the surface species with X-ray absorption spectroscopy, atomic resolution electron microscopy, and electronic structure theory, we have differentiated among the MgO surface sites for iridium bonding. The results demonstrate the contrasting structures and catalytic properties of samples, even including those incorporating iridium at loadings as low as 0.01 wt % and showing that the latter are nearly ideal in the sense of having almost all the Ir atoms at equivalent surface sites, with each Ir atom bonded to three oxygen atoms of the MgO surface. These supported molecular catalysts are modeled accurately with density functional theory. The results open the door to the precise synthesis of families of single-site catalysts. The work was supported by the U.S. Department of Energy (DOE), Office of Science (SC), Basic Energy Sciences (BES), Grant DE-FG02-04ER15513 and the DOE BES Catalysis Center Program by a subcontract from Pacific Northwest National Laboratory (KC0301050-47319) to the University of Alabama. We thank Chevron for fellowship support of ASH and LMD. DAD thanks the Robert Ramsay Chair Fund of The University of Alabama for support. A portion of the research was performed using facilities of the Environmental Molecular Sciences Laboratory (Ringgold ID 130367), a DOE SC User Facility sponsored by the Office of Biological and Environmental Research. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by DOE SC BES under Contract No. DE-AC02- 76SF00515. We thank Chevron Energy Technology Company for performing the XRD experiments.

single-site catalyst, iridium catalyst, MgO-suppor↗
DOE OSTI2022

Boosting the H 2 –D 2 Exchange Activity of Dilute Nanoporous Ti–Cu Catalysts through Oxidation–Reduction Cycle–Induced Restructuring

The use of nanoporous metals as catalysts has attracted significant interest in recent years. Their high-curvature, nanoscale ligaments provide not only high surface area but also a high density of undercoordinated step edge and kink sites. However, their long-term stability, especially at higher temperatures, is often limited by thermal coarsening and the associated loss of surface area. Herein, it is demonstrated that the nanoscale morphology of nanoporous Cu can be regenerated by applying oxidation/reduction cycles at 250 °C. Specifically, the morphological evolution and H 2 dissociation activity of hierarchical nanoporous Cu catalysts doped with Ti during structural rearrangement triggered by oxidative and reductive atmospheres at elevated temperatures are studied. In addition to coarsening of the structure at elevated temperatures, oxidation at 400 °C causes an expansion of the ligaments. Further, subsequent reduction at 400 °C leads to the formation of particles and a drop in the H 2 dissociation activity compared the fresh catalyst. However, performing the redox cycle at 250 °C reverses coarsening and boosts the H 2 dissociation activity for the hydrogen–deuterium (H 2 –D 2 ) reaction. Herein, the possibility to reverse coarsening is demonstrated, thereby mitigating the loss of activity frequently observed in nanoporous catalysts.

36 MATERIALS SCIENCE↗
DOE OSTI2026

MoS 2 Catalysts Selectively Achieve High Yield of Liquid Oxygenate from Direct Conversion of Methane via Hydroxyl Radicals

Directly converting methane (CH 4 ) into liquid oxygenates (e.g., methanol) can circumvent the cost and engineering limits of natural gas transportation and storage. However, oxygenate yields from CH 4 remain low, and sulfur present in natural gas hinders activity in most catalysts. Here, to overcome these barriers, we employ bulk molybdenum disulfide (MoS 2 ), a low-cost, robust catalyst which selectively produces large quantities of liquid oxygenates (>900 µmol/g cat ∙hr) from methane in the presence of hydroxyl (OH • ) radicals produced from dilute hydrogen peroxide (H 2 O 2 ) at 75°C. Under realistic reaction conditions, MoS 2 partially and reversibly adopts a metastable, more electrically conductive phase (1T’) that can only be observed through in situ structural probes. Herein, we elucidate that redox synergy between H 2 O 2 and MoS 2 produces active OH • radical species that selectively transform CH 4 to surface methoxy species at the gas-solid liquid interface, leading to the unitary production of liquid oxygenate at a rate competitive with more costly precious metal catalysts, without additional catalyst preparation steps.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Ionic Precursors Transformed Into Vinyl Acetate Synthesis Catalyst via Reaction-Driven Restructuring

Conventional preparation of supported bimetallic catalysts relies on solution-mediated metal salt immobilization and pre-formation of alloy nanoparticles before reaction. Here, we report a fundamentally different synthesis strategy of using a physical mixture of salt precursors to generate an active catalyst during reaction. The catalytic structure is generated in situ from Pd3(OAc)6, Au(OH)3, and KOAc through H2 treatment and reaction-driven restructuring under vinyl acetate monomer (VAM) synthesis conditions. Ascertained from in situ X-ray diffraction and operando infrared spectroscopy analyses, reduction treatment produces segregated Pd and Au domains, and subsequent exposure to a VAM reaction mixture triggers dynamic extraction of Pd from the metal surface. This latter process, mediated by acetate-assisted redox cycles, facilitates Pd migration toward Au domains to form a near-surface localized Pd50Au50 alloy phase. Monometallic Pd domains serve as a reservoir of Pd to the alloy phase, leading to and sustaining a more Pd-enriched active surface and a higher population of accessible Pd sites, compared to a conventionally prepared K-PdAu/SiO2 catalyst. Consequently, this leads to a twofold increase in the VAM formation rate, demonstrating highly active bimetallic catalysts can be generated through the gas-phase treatment of physically mixed ionic precursors.

Cha, Byeong Jun [Rice University]↗
DOE OSTI2018

The Absence and Importance of Operando Techniques for Metal-Free Catalysts

Operando characterization techniques have played an important role in modern technological developments. In contrast to the experimental uncertainties introduced by ex situ techniques, the simultaneous measurement of desired sample characteristics and near-realistic electrochemical testing provides a representative picture of the underlying physics. From Li-ion batteries to metal-based electrocatalysts, the insights offered by real-time characterization data have enabled more efficient research programs. As an emerging class of catalyst, much of the mechanistic understanding of metal-free electrocatalysts continues to be elusive in comparison to their metal-based counterparts. Yet, there is a clear absence of operando characterization performed on metal-free catalysts. Through the proper execution of operando techniques, it can be expected that metal-free catalysts can achieve exceptional technological progress. Here, the motivation of using operando characterization techniques for metal-free carbon-based catalyst system is considered, followed by a discussion of the possibilities, difficulties and benefits of their applications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Direct Characterization of Atomically Dispersed Catalysts: Nitrogen-Coordinated Ni Sites in Carbon-Based Materials for CO 2 Electroreduction

Metal, nitrogen-doped carbon materials have attracted interest as heterogenous catalysts that contain MN x active sites that are analogous to molecular catalysts. Of particular interest is Ni,N-doped carbon, a catalyst that is active for the electrochemical reduction of CO 2 to CO. Critical to the understanding of these materials is proof of single atomic sites and characterization of the environment surrounding the metal atom; however, directly probing this coordination remains challenging. This challenge is addressed in this study by combining scanning transmission electron microscopy (STEM), single atom electron energy loss spectroscopy (EELS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Through STEM imaging, atomic dispersion of Ni in the carbon framework is confirmed and image analyses are utilized to give semiquantitative estimates of neighbor distance distributions and site densities of Ni atoms. Atomic resolution EELS demonstrates that N and Ni are colocated at the single Ni atom sites suggesting Ni–N coordination. ToF-SIMS reveals a distribution of NiN x C y - fragments that reflect the Ni–N bonding environments within Ni,N-doped carbon. The fragmentation from Ni,N-doped carbon is similar to Ni phthalocyanine, suggesting the existence of heterogenized, molecular-like NiN 4 active sites which motivates future studies that leverage insight from molecular catalysis design to develop next-generation heterogeneous catalysts.

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

Ultrathin Microporous Transport Layers: Implications for Low Catalyst Loadings, Thin Membranes, and High Current Density Operation for Proton Exchange Membrane Electrolysis

Porous transport layers (PTL) and their surface properties have the potential to improve the performance of proton exchange membrane water electrolyzers (PEMWE), which is imperative to reduce feedstock costs and lead to their widespread implementation. This work introduces a novel generation of titanium microporous layers (MPLs) with ultra-low thicknesses of approx. 20 um which reduces raw material costs. They also feature advanced interfacial properties tailored to maximize catalyst utilization at low Ir-loadings. The bulk morphology and surface properties of the hierarchically structured PTLs are assessed by X-ray tomographic microscopy. The low surface roughness of the MPL allows the use of thinner membranes since it minimizes possible deformations in the membrane. Cells containing the MPLs outperformed those containing state-of-the-art commercially available PTL materials by up to 100 mV at 7 A cm-2 in combination with low-loaded catalyst-coated membranes of 0.4 mgIr cm-2. Hydrogen crossover is also reduced, especially at low current densities, leading to a larger turndown ratio which can enable more cost-effective operating strategies. Finally, these rationally designed MPLs also lead to high catalyst utilization by overcoming the naturally occurring high in-plane resistance of low-loaded catalyst layers.

hydrogen crossover↗
DOE OSTI2026

Hybrid Ionomer-Free Porous Transport Electrodes With Catalyst Coated Membranes for Enhanced Water Electrolysis

To promote industrial uptake of clean hydrogen production technologies such as polymer electrolyte membrane (PEM) water electrolyzers, advancements in catalyst layer (CL) morphology are required. We demonstrate how improved electrochemical performance can be achieved when using an ionomer free porous transport electrode (PTE) coupled with a traditional catalyst coated membrane (CCM) assembly in PEM water electrolyzers. Notably, we reveal that the superior performance achieved when utilizing a hybrid PTE and CCM assembly is due to enhanced ohmic performance caused by optimal contact with both the porous transport layer (PTL) and PEM interfaces. Using operando neutron radiography, we demonstrate that configurations utilizing a CCM resulted in more rapid water replenishment to reaction sites, indicating enhanced membrane hydration beneficial for performance. This enhanced membrane hydration coupled with improved contact area at the PEM-catalyst layer (CL) and PTL-CL interfaces was revealed through the reduced ohmic overpotentials of the hybrid PTE-CCM design, which achieved the lowest ohmic overpotential of 431 mV at 2000 mA cm−2. While the average in-plane water distributions are generally similar between cell configurations, we reveal that utilizing a PTE configuration promotes a more homogenous water distribution near the CL-membrane interface due to enhanced catalyst utilization.

Seip, Tess [ORNL] (ORCID:0000000232740594)↗
DOE OSTI2021

Effects of surface species and homogeneous reactions on rates and selectivity in ethane oxidation on oxide catalysts

Selective alkane oxidations on metal oxide catalysts involve complex mechanisms with multiple reactions in series and parallel, different types of reduced and oxidized surface species, and potential contributions from gas-phase reactions. We report kinetics and thermodynamics of elementary steps involved in C 2 H 6 -O 2 reactions on SiO 2 -supported small vanadium oxide domains are determined using density functional theory. These surface reactions together with gas-phase mechanisms are incorporated in kinetic simulations to determine how surface and gaseous reactions interact and contribute to rates and selectivity. The results show that gas-phase reactions within pore volumes in contact with the catalyst contribute significantly to C 2 H 6 activation rates, even at conditions where gas-phase reactions in empty volumes without catalyst are negligible. The majority of C 2 H 6 activations occur on the surface, via H abstraction by vanadium oxo species present at terminal lattice oxygens. The gas-phase activations via H-abstraction by OH radicals also exhibit significant contributions. The reduced centers formed by reactions at vanadium oxo species are re-oxidized rapidly and, therefore, are present in very small concentrations at reaction conditions. The re-oxidation steps lead to the formation of HO 2 radicals and surface peroxo species that are also rapidly consumed and are present in small concentrations. The peroxo species preferentially convert C 2 H 4 to its epoxide product and influence selectivity even at low concentrations. The gas-phase reactions decrease the concentrations of peroxo species and improve selectivity slightly. The effects of reaction conditions and catalyst site density provide further insights into how factors beyond conversions at lattice oxygens influence rates and selectivity in alkane oxidation reactions of significant industrial importance.

42 ENGINEERING↗
DOE OSTI2015

Chemo‐ and Regioselective Hydrogenolysis of Diaryl Ether C−O Bonds by a Robust Heterogeneous Ni/C Catalyst: Applications to the Cleavage of Complex Lignin‐Related Fragments

Abstract We report the chemo‐ and regioselective hydrogenolysis of the C−O bonds in di‐ ortho ‐substituted diaryl ethers under the catalysis of a supported nickel catalyst. The catalyst comprises heterogeneous nickel particles supported on activated carbon and furnishes arenes and phenols in high yields without hydrogenation. The high thermal stability of the embedded metal particles allows C−O bond cleavage to occur in highly substituted diaryl ether units akin to those in lignin. Preliminary mechanistic experiments show that this catalyst undergoes sintering less readily than previously reported catalyst particles that form from a solution of [Ni(cod) 2 ].

Gao, Fang↗
DOE OSTI2018

Evidence for Dynamic Chemical Kinetics at Individual Molecular Ruthenium Catalysts

Abstract Catalytic cycles are typically depicted as possessing time‐invariant steps with fixed rates. Yet the true behavior of individual catalysts with respect to time is unknown, hidden by the ensemble averaging inherent to bulk measurements. Evidence is presented for variable chemical kinetics at individual catalysts, with a focus on ring‐opening metathesis polymerization catalyzed by the second‐generation Grubbs’ ruthenium catalyst. Fluorescence microscopy is used to probe the chemical kinetics of the reaction because the technique possesses sufficient sensitivity for the detection of single chemical reactions. Insertion reactions in submicron regions likely occur at groups of many (not single) catalysts, yet not so many that their unique kinetic behavior is ensemble averaged.

Easter, Quinn T.↗
DOE OSTI2018

Stabilized Vanadium Catalyst for Olefin Polymerization by Site Isolation in a Metal–Organic Framework

Abstract Vanadium catalysts offer unique selectivity in olefin polymerization, yet are underutilized industrially owing to their poor stability and productivity. Reported here is the immobilization of vanadium by cation exchange in MFU‐4 l , thus providing a metal–organic framework (MOF) with vanadium in a molecule‐like coordination environment. This material forms a single‐site heterogeneous catalyst with methylaluminoxane and provides polyethylene with low polydispersity (PDI≈3) and the highest activity (up to 148 000 h −1 ) reported for a MOF‐based polymerization catalyst. Furthermore, polyethylene is obtained as a free‐flowing powder as desired industrially. Finally, the catalyst shows good structural integrity and retains polymerization activity for over 24 hours, both promising attributes for the commercialization of vanadium‐based polyolefins.

Comito, Robert J.↗
DOE OSTI2019

Atomically Dispersed Molybdenum Catalysts for Efficient Ambient Nitrogen Fixation

Abstract NH 3 synthesis by the electrocatalytic N 2 reduction reaction (NRR) under ambient conditions is an appealing alternative to the currently employed industrial method—the Haber–Bosch process—that requires high temperature and pressure. We report single Mo atoms anchored to nitrogen‐doped porous carbon as a cost‐effective catalyst for the NRR. Benefiting from the optimally high density of active sites and hierarchically porous carbon frameworks, this catalyst achieves a high NH 3 yield rate (34.0±3.6 μg h −1 mg cat. −1 ) and a high Faradaic efficiency (14.6±1.6 %) in 0.1 m KOH at room temperature. These values are considerably higher compared to previously reported non‐precious‐metal electrocatalysts. Moreover, this catalyst displays no obvious current drop during a 50 000 s NRR, and high activity and durability are achieved in 0.1 m HCl. The findings provide a promising lead for the design of efficient and robust single‐atom non‐precious‐metal catalysts for the electrocatalytic NRR.

Han, Lili↗
DOE OSTI2020

Radical Chemistry and Reaction Mechanisms of Propane Oxidative Dehydrogenation over Hexagonal Boron Nitride Catalysts

Abstract Although hexagonal boron nitride (h‐BN) has recently been identified as a highly efficient catalyst for the oxidative dehydrogenation of propane (ODHP) reaction, the reaction mechanisms, especially regarding radical chemistry of this system, remain elusive. Now, the first direct experimental evidence of gas‐phase methyl radicals (CH 3 . ) in the ODHP reaction over boron‐based catalysts is achieved by using online synchrotron vacuum ultraviolet photoionization mass spectroscopy (SVUV‐PIMS), which uncovers the existence of gas‐phase radical pathways. Combined with density functional theory (DFT) calculations, the results demonstrate that propene is mainly generated on the catalyst surface from the C−H activation of propane, while C 2 and C 1 products can be formed via both surface‐mediated and gas‐phase pathways. These observations provide new insights towards understanding the ODHP reaction mechanisms over boron‐based catalysts.

Zhang, Xuanyu↗