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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.

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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Au and Pt nanoparticle supported catalysts tailored for H-2 production: From models to powder catalysts

The use of metal nanoparticles (NPs), including Au and Pt, supported over oxides has been pivotal, and is ever increasing in enabling catalytic reactions which target the production of hydrogen. We review here the most recent works pertaining to the fundamental understanding of the structure, morphology, growth, characterization, and intrinsic phenomenological properties of Au– and Pt– based catalysts that influence the reactivity and selectivity to target hydrogen production. We draw on surface science and theoretical methods of model and powder catalysts using high resolution imaging, spectroscopy, scattering experiments, and theoretical studies. Based on these insights we identify key aspects of studies of supported metal nanoparticle (NP) catalysts for several reactions. The main focus of this review is on the intersection of catalytic chemistry related to the water-gas shift (WGS), oxygenate steam reforming (OSR), and solarassisted reactions (SAR).

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

2,4,6-Triphenylpyridinium-Substituted Neutral Nickel Catalysts: Ethylene Polymerization, Influence of Activator, Catalyst Decomposition, and End-Group Analysis

The reactivity of 2,4,6-triphenylpyridinium-substituted nickel(II)-salicyliminato catalysts in ethylene polymerization has been explored. Here, the known complex 6a equipped with a 2,6-diisopropylphenyl group affords polyethylene with M n = 10-12 kDa at 19 ⁰C, while 8a possessing the bulkier 2,6-diphenylphenyl moiety gives polymer with M n = 270-310 kDa. The stability of catalyst 6a depends on the borane activator. If B(C 6 F 5 ) 3 is employed, enhanced stability is observed compared with using 3H 2 O·B(C 6 F 5 ) 3 activator. Catalyst 6a decomposes forming a hydroxyl-bridged dimer 14 which may be reac-tivated, albeit inefficiently, by excess borane activator. Polymer formed by 6a contains ca. 3-6% of 2-trifluoromethylphenyl, pentafluorophenyl, and 3,5-bis(trifluoromethyl)phenyl end groups combined. The pentafluoro-phenyl end group originates from reaction of 6a with borane activator, and from reactivation of hydroxyl-bridged dimer 14. 3,5-Bis(trifluoromethyl)phenyl end groups are likely formed in a reaction sequence initiated by protonation of one aryl group in NaBArF which creates B[C 6 H 3 (CF 3 ) 2 ] 3 . The triarylborane can then react with 6a or 14 transferring the 3,5-bis(trifluoromethyl)phenyl group to nickel.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Low-Temperature Methane Partial Oxidation to Syngas with Modular Nanocrystal Catalysts [Targeting Low-Temperature Methane Partial Oxidation to Syngas with Modular Nanocrystal Catalysts]

Here, the low-temperature conversion of methane into value-added products is an appealing goal due to the abundance of methane in the form of natural gas. Industrially, methane is used to produce synthesis gas (syngas), a precursor mixture used heavily in the production of ammonia, methanol, and synthetic fuels. In practice, this mixture is produced via the energy-intensive methane steam reforming reaction at temperatures between 750 and 1450 °C. The exothermic methane partial oxidation reaction stands as an alternative for syngas formation at lower temperatures, especially for gas to liquid fuels applications, yet awaits large-scale implementation due to dangerous operating conditions and temperatures. Using colloidally synthesized Ru catalysts, we identify two unifying rules that govern the low-temperature production of synthesis gas: depletion of oxygen within the catalyst bed and facile RuO 2 → Ru reduction kinetics, which is a strong function of supporting material and Ru nanostructure. Using these design rules, we demonstrate the enhanced low-temperature activity of a bifunctional Ru/Pd catalyst which produces synthesis gas at ~400 °C, with nearly complete CH 4 conversion and CO selectivity at 670 °C.

03 NATURAL GAS↗
DOE OSTI2021

Understanding the Correlation between Ga Speciation and Propane Dehydrogenation Activity on Ga/H-ZSM-5 Catalysts

H-ZSM-5 zeolite-supported Ga (Ga/H-ZSM-5) has been considered as a selective catalyst for nonoxidative propane dehydrogenation (PDH) for decades; however, the reaction mechanism remains a topic of considerable discussion. In particular, the correlation between various Ga species present on the catalyst at the reaction conditions and the PDH activity has yet to be established. In this work, intrinsic PDH rates and activation energies were determined on Ga + –H + pair sites and isolated Ga + sites on Ga/H-ZSM-5 samples with a wide range of Si/Al and Ga/Al ratios. Here, the turnover frequency on Ga + –H + pair sites in the PDH is higher than that of isolated Ga + sites by a factor of ~15. Experimental measurements combined with a dual-site model show the activation energy in the PDH on the Ga + –H + pair sites and isolated Ga + sites to be 90.8 ± 1.5 and 117 ± 4.7 kJ·mol –1 , respectively. These results demonstrate that Ga+–H+ pair sites are much more active in the PDH than isolated Ga + sites. The activation energy of GaH x decomposition to form H 2 was determined to be 40–60 kJ·mol –1 higher than that of the PDH on Ga species, suggesting that the GaH x decomposition is unlikely to be part of the PDH mechanism. Although both Brønsted acid and Ga sites interact with propane, Fourier transform infrared spectroscopy results provide strong evidence suggesting that the alkyl mechanism is more likely in the PDH on Ga/H-ZSM-5 catalysts.

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

Cascade Reaction of Ethanol to Butadiene over Ag-Promoted, Silica- or Zeolite-Supported Ta, Y, Pr, or La Oxide Catalysts

Ethanol converts to 1,3-butadiene in the presence of suitable multifunctional catalysts. In this work, Lewis acid cations Ta, Y, Pr, and La were dispersed on amorphous silica or beta zeolite, and after physically mixing with silica-supported Ag nanoparticles, were tested in the cascade reaction of ethanol to butadiene at 573 K. The Lewis acid catalysts were characterized by X-ray fluorescence, N 2 physisorption, scanning transmission electron microscopy (STEM), X-ray diffraction, diffuse reflectance (DR) UV-Vis and X-ray photoelectron spectroscopy. High-resolution STEM images confirmed the small oxide cluster size on the silica support. Results from DR UV-Vis spectroscopy showed zeolite-supported Ta and Pr catalysts had a smaller metal oxide cluster size, relative to their SiO 2 counterparts. X-ray photoelectron spectroscopy confirmed the oxidation state of the cations supported on the zeolite remained the same as that of their SiO 2 -supported analogues. The selectivity of the C 4 coupling products toward butadiene relative to butanol correlated with acid strength of the Lewis acid cations, as evaluated by the 2-propanol decomposition reaction to propene and acetone, with Ta being the most selective. In conclusion, the rate of C-C coupling over the zeolite-supported cations was enhanced by an order of magnitude compared to those cations supported on amorphous SiO 2 .

C-C bond formation↗
DOE OSTI2024

Ethanol Upgrading with N,N,N -Pincer-Based Ru Catalysts: Delineating Key Factors Governing Catalyst Evolution and Stability

The 5-CH 3 -bpi (bpi = 1,3-bis(2'-pyridylimino)isoindolate) ruthenium catalyst is among the most active catalysts to generate higher order alcohols from ethanol, via the Guerbet reaction, yet the reason(s) for this beneficial CH 3 -subsitution position (5- relative to 4- and 6-) were not known. To understand the influence of this unique positional activity, we report a mechanistic investigation of the N,N,N-pincer Ru(bpi)(PPh 3 ) 2 Cl catalyst. In situ IR and ex situ NMR/ESI-MS analyses of catalytic reactions identified a series of Ru carbonyl species generated during catalysis. Here, we find that the primary decomposition pathway is via hydrogenolysis of the bpi ligands and that incorporating a methyl group at the 5-position disfavors this deactivation pathway.

(de)hydrogenation↗
DOE OSTI2019

Brønsted Acid Scaling Relationships Enable Control over Product Selectivity from O2 Reduction with a Mononuclear Cobalt Porphyrin Catalyst

The selective reduction of O2, typically with the goal of forming H2O, represents a long-standing challenge in the field of catalysis. Macrocyclic transition-metal complexes, and cobalt porphyrins in particular, have been the focus of extensive study as catalysts for this reaction. Here, we show that the mononuclear Co-tetraarylporphyrin complex, Co(porOMe) (porOMe = meso-tetra(4-methoxyphenyl)porphyrin), catalyzes either 2e-/2H+ or 4e-/4H+ reduction of O2 with high selectivity simply by changing the identity of the Bronsted acid in dimethylformamide (DMF). The thermodynamic potentials for O2 reduction to H2O2 or H2O in DMF are determined and exhibit a Nernstian dependence on the acid pKa, while the CoIII/II redox potential is independent of the acid pKa. The reaction product, H2O or H2O2, is defined by the relationship between the thermodynamic potential for O2 reduction to H2O2 and the CoIII/II redox potential: selective H2O2 formation is observed when the CoIII/II potential is below the O2/H2O2 potential, while H2O formation is observed when the CoIII/II potential is above the O2/H2O2 potential. Mechanistic studies reveal that the reactions generating H2O2 and H2O exhibit different rate laws and catalyst resting states, and these differences are manifested as different slopes in a linear free energy correlation between the log(rate) vs. effective overpotential for the reactions. This work shows how the manipulation of thermodynamic scaling relationships may be used to control product selectivity, and it provides a mechanistic basis for the pursuit of molecular catalysts that achieve low overpotential reduction of O2 to H2O.

Wang, Yu-Heng↗
DOE OSTI2024

Methyl Termination of p-Type Silicon Enables Selective Photoelectrochemical CO 2 Reduction by a Molecular Ruthenium Catalyst

Methyl-terminated p-type silicon photoelectrodes selectively drive CO 2 reduction by a homogeneous [Ru(tpy)(Mebim-py)(NCCH 3 )] 2+ catalyst (tpy = 2,2′:6′,2″-terpyridine, Mebim-py = 1-methylbenzimidazol-2-ylidene-3-(2′-pyridine)). A 460 mV photovoltage is quantified for the photoelectrode. Under 1 sun illumination, this system achieves a Faradaic efficiency of 87% for CO at −1.7 V vs Fc +/0 , matching reports of the same catalyst at metallic electrodes operating at −2.1 V. When 5% water is introduced, the CH 3 -terminated Si photoelectrode remains stable, selectivity for CO is retained, and current density increases. Methyl termination suppresses the competitive hydrogen evolution observed for H-terminated Si photoelectrodes, which under the same conditions produce ca. 60% CO and 8% H 2 and have unstable performance. Furthermore, these results establish that a semiconductor photoelectrode can power a molecular CO 2 reduction catalyst without hydrogen evolution by the photoelectrode itself. Methyl termination of p-Si allows CO 2 reduction to kinetically outcompete proton reduction, revealing an important design principle for selective fuel formation.

Catalysts↗
DOE OSTI2022

Plasma-Catalyst Reactivity Control of Surface Nitrogen Species through Plasma-Temperature-Programmed Hydrogenation to Ammonia

Nonthermal plasma activation of N 2 can facilitate nitrogen adsorption on metal catalysts at low bulk temperatures and atmospheric pressure. Here, we apply a plasma-assisted temperature-programmed reaction (plasma-TPRxn) for ammonia (NH 3 ) synthesis using sequential exposure of a silica-supported metal catalyst to N 2 plasma followed by thermal hydrogen treatment while ramping the temperature to decouple the plasma activation of N 2 from surface catalyzed hydrogenation steps. This approach eliminates the effects from bulk plasma phase reactions, thereby allowing for direct interrogation of plasma activated nitrogen on the active metal surfaces. We confirm previously reported spectroscopic observations that show plasma-generated surface nitrogen can be converted to NH 3 through surface catalyzed pathways. Further, we demonstrate that the ammonia desorption peak temperature is sensitive to metal, with Pt desorbing NH 3 at the lowest temperature. Unsteady state microkinetic models of desorption kinetics as a function of initial N coverage and metal recover observed trends in NH 3 desorption temperatures and confirm that observed results reflect hydrogenation of plasma-induced N accommodation at each surface. In total, we show that the hydrogenation ability of the catalyst after plasma activation of N 2 is responsible for the reactivity trends observed in plasma-assisted NH 3 synthesis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Active Hydrogenation Catalyst with a Structured, Peptide-Based Outer-Coordination Sphere

The synthesis, catalytic activity, and structural features of a rhodium-based hydrogenation catalyst containing a phosphine ligand coupled to a 14-residue peptide are reported. Both CD and NMR spectroscopy show that the peptide adopts a helical structure in 1:1:1 TFE/MeCN/H2O that is maintained when the peptide is attached to the ligand and when the ligand is attached to the metal complex. The metal complex hydrogenates aqueous solutions of 3-butenol to 1-butanol at 360 ± 50 turnovers/Rh/h at 294 K. This peptide- based catalyst represents a starting point for developing and characterizing a peptide-based outer-coordination sphere that can be used to introduce enzyme-like features into molecular catalysts. This work was funded by the US DOE Basic Energy Sciences, Chemical Sciences, Geoscience and Biosciences Division (AJ, JCL and WJS), the Office of Science Early Career Research Program through the Office of Basic Energy Sciences (GWB, MLR and WJS). Part of the research was conducted at the W.R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by U.S. Department of Energy’s Office of Biolog-ical and Environmental Research (BER) program located at Pacific Northwest National Laboratory (PNNL). PNNL is operated by Battelle for the U.S. Department of Energy.

amino acid catalysts↗