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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Rhodium Bis(quinolinyl)benzene Complexes for Methane Activation and Functionalization

A series of rhodium (III) bis(quinolinyl)benzene (bisq x ) complexes was researched as candidates for the homogeneous partial oxidation of methane. Density functional theory (DFT) (M06 with Poisson continuum solvation) was used to investigate a variety of (bisq x ) ligand candidates involving different functional groups to determine the impact on RhIII(bisq x ) catalyzed methane functionalization. The free energy activation barriers for methane C–H activation and Rh–methyl functionalization at 298 K and 498 K were determined. DFT studies predict that the best candidate for catalytic methane functionalization is Rh III coordinated to unsubstituted bis(quinolinyl)benzene (bisq). Support is also found for the prediction that the η 2 -benzene coordination mode of (bisq x ) ligands on Rh encourages methyl group functionalization by serving as an effective leaving group for S N 2 and S R 2 attack.

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DOE OSTI2016

Rhodium pair-sites on magnesium oxide: Synthesis, characterization, and catalysis of ethylene hydrogenation

Supported rhodium acetate dimers were prepared by the reaction of Rh2(OAc)4 (OAc is acetate) with highly dehydroxylated MgO powder and characterized by extended X-ray absorption fine structure and infrared (IR) spectra, which show that the supported species were well represented as Rh2(OAc)3, with each Rh atom on average bonded to one oxygen atom of the MgO surface. Aberration-corrected scanning transmission electron microscopy gave images of Rh atoms in pairs on the MgO. The supported rhodium dimers were probed with a pulse of CO, and the IR spectra indicate a Rh(II) species with weakly bonded carbonyl ligands; the sharpness of the νCO band indicates highly uniform surface species. Further treatment in CO led to breakup of the rhodium dimers into mononuclear species; such fragmentation took place in other treatment gases as well, with the degree of fragmentation decreasing in the order CO > C2H4 > helium. The fragmentation is inferred on the basis of IR spectra to have proceeded through intermediate Rh2 species without acetate ligands. In contrast, rhodium dimers were reduced and not fragmented in the presence of H2 at 353 K, but at higher temperatures the rhodium aggregated to give larger clusters. The supported species catalyzed ethylene hydrogenation at 298 K and 1 bar at a H2 to ethylene molar ratio of 4; after 27 h of catalysis in a once-through flow reactor, acetate ligands were removed from the dimers, and some of them fragmented, as shown by IR spectroscopy. The intermediate dirhodium species without acetate ligands are two or three orders of magnitude more active as catalysts than the supported mononuclear rhodium species or those present predominantly as Rh2(OAc)3, respectively.

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DOE OSTI2022

Large exotic spin torques in antiferromagnetic iron rhodium.

Spin torque is a promising tool for driving magnetization dynamics for computing technologies. These torques can be easily produced by spin-orbit effects, but for most conventional spin source materials, a high degree of crystal symmetry limits the geometry of the spin torques produced. Magnetic ordering is one way to reduce the symmetry of a material and allow exotic torques, and antiferromagnets are particularly promising because they are robust against external fields. We present spin torque ferromagnetic resonance (ST-FMR) measurements and second harmonic Hall measurements characterizing the spin torques in anti -ferromagnetic iron rhodium alloy. We report extremely large, strongly temperature-dependent exotic spin torques with a geometry apparently defined by the magnetic ordering direction. We find the spin torque efficiency of iron rhodium to be (207 +/- 94)% at 170 K and (88 +/- 32)% at room temperature. We support our conclusions with theoretical calculations showing how the antiferromagnetic ordering in iron rhodium gives rise to such exotic torques.

Gibbons, Jonathan↗
DOE OSTI2016

Intrinsic selectivity and structure sensitivity of Rhodium catalysts for C 2+ oxygenate production [On the intrinsic selectivity and structure sensitivity of Rhodium catalysts for C 2+ oxygenate production]

Synthesis gas (CO + H 2 ) conversion is a promising route to converting coal, natural gas, or biomass into synthetic liquid fuels. Rhodium has long been studied as it is the only elemental catalyst that has demonstrated selectivity to ethanol and other C 2+ oxygenates. However, the fundamentals of syngas conversion over rhodium are still debated. In this work a microkinetic model is developed for conversion of CO and H 2 into methane, ethanol, and acetaldehyde on the Rh (211) and (111) surfaces, chosen to describe steps and close-packed facets on catalyst particles. The model is based on DFT calculations using the BEEF-vdW functional. The mean-field kinetic model includes lateral adsorbate–adsorbate interactions, and the BEEF-vdW error estimation ensemble is used to propagate error from the DFT calculations to the predicted rates. The model shows the Rh(211) surface to be ~6 orders of magnitude more active than the Rh(111) surface, but highly selective toward methane, while the Rh(111) surface is intrinsically selective toward acetaldehyde. A variety of Rh/SiO 2 catalysts are synthesized, tested for catalytic oxygenate production, and characterized using TEM. The experimental results indicate that the Rh(111) surface is intrinsically selective toward acetaldehyde, and a strong inverse correlation between catalytic activity and oxygenate selectivity is observed. Furthermore, iron impurities are shown to play a key role in modulating the selectivity of Rh/SiO 2 catalysts toward ethanol. The experimental observations are consistent with the structure-sensitivity predicted from theory. As a result, this work provides an improved atomic-scale understanding and new insight into the mechanism, active site, and intrinsic selectivity of syngas conversion over rhodium catalysts and may also guide rational design of alloy catalysts made from more abundant elements.

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DOE OSTI2021

Economizing on Precious Metals in Three-Way Catalysts: Thermally Stable and Highly Active Single-Atom Rhodium on Cera for NO Abatement under Dry and Industrially Relevant Conditions

We show for the first time that atomically dispersed Rh cations on ceria, prepared via high-temperature atom trapping synthesis, are the active species for (CO+NO) reaction. This provides a direct link with the organometallic homogeneous Rh(I) complexes capable of catalyzing dry (CO+NO) reaction but without the stability concern. In particular, thermally stable Rh cations in 0.1wt% Rh1/CeO2 achieve full NO conversion with a TOF of ~ 330 hr-1 per Rh atom at 120 °C. Under dry conditions, the main product above 100 °C is N2 with N2O being the minor product. The presence of water promotes low-temperature activity of 0.1wt% Rh1/CeO2 starting at 50 °C with full NO conversion at ~120 °C. In the case with the wet stream, however, ammonia and nitrogen are the main products with only minor N2O amounts. NH3 formation at such low temperatures is attractive because of the potential to use this as a passive SCR system. Because of the uniformity of Rh ions on the support, we are able to observe the intermediates of (CO+NO) reaction via infrared measurements on Rh cations on zeolite and ceria. Furthermore, we show that ammonia formation correlates with the WGS activity of the material and thus, rhodium hydride Rh-H species are involved in this reaction: we detect Rh(CO)Hx species on ceria using isotopic IR measurements. These findings provide new mechanistic understanding for the catalytically active species in TWC catalysis and open up a new avenue for the synthesis of novel emissions control catalysts with 100% atom economy of ultra-expensive precious metals such as Rh.

Khivantsev, Konstantin↗
DOE OSTI2016

Electrocatalytic Hydrogenation of Phenol over Platinum and Rhodium: Unexpected Temperature Effects Resolved

Both electrocatalytic hydrogenation (ECH) and thermal hydrogenation (TH) of phenol by Pt and Rh show a roll-over in rate with increasing temperature without changing the principal reaction pathways. The negative effect of temperature for aqueous-phase phenol H2 and electrocatalytic hydrogenation on Pt and Rh is deduced to be due to the unexpected buildup of dehydrogenated phenol adsorbates, which block active sites. Rates of ECH and TH increase similarly with increasing hydrogen chemical potential whether induced by applied potential or H2 pressure, both via increasing H coverage, and indirectly by removing site blockers, a very strong effect at high temperature. This enables unprecedented rates in the TH of phenol at these temperatures.

Electrocatalysis↗
DOE OSTI2017

(Pentamethylcyclopentadienato)rhodium complexes for delivery of the curcumin anticancer drug [Rhodium pentamethylcyclopentadienato complexes for delivery of the curcumin anti-cancer drug]

[RhIII(*Cp)Cl(X,Y)] n+ complexes {X, Y = Cl, PTA, n = 0 (2); X, Y = en, n = 1 (3, Cl– salt; 4, PF 6 – salt); X, Y = acac, n = 0 (5); X, Y = cur, n = 0 (6), where *Cp = pentamethylcyclopentadienato, curH = curcumin; PTA = 1,3,5-triaza-7-phosphatricyclo[3.3.1.1]decane; en = 1,2-ethanediamine; acac = acetylacetonato = 2,4-pentanedionato(1–)} were synthesized from [Rh(*Cp)(µ-Cl)Cl] 2 (1). While 2–5 were inactive against human epithelial A549 lung-cancer cells in assays of cytotoxicity, and antimetastatic and proapoptotic behaviors, 6 had a cytotoxic activity similar to that of curH over 72 h, but at 24 h in real-time cell migration assays, it was less active, showing slow release of curH. All complexes underwent ligand-exchange reactions with biomolecules and cells within the timeframes of the assays (X-ray absorption spectroscopy). Intracellular elemental distributions (X-ray fluorescence microscopy) showed that 6 effectively delivered curH to cells, where it was released. Other elemental distributions and caspase activities were consistent with preapoptotic activities. As such, 6 is a promising delivery agent for bioactive ligands, such as curH. However, pure curcumin itself showed a previously unrecognized ability to promote migration of A549 cells at subtoxic concentrations in the presence of endothelial growth factor, which may be a concern for its widespread use as a nutritional supplement and as a potential drug. As a result, this aspect warrants further research.

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DOE OSTI2017

Mechanistic Studies of Single-Step Styrene Production Using a Rhodium(I) Catalyst

The direct and single-step conversion of benzene, ethylene, and a Cu(II) oxidant to styrene using the Rh(I) catalyst ( Fl DAB)Rh(TFA)(η 2 -C 2 H 4 ) [ Fl DAB = N,N '-bis(pentafluorophenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene; TFA = trifluoroacetate] has been reported to give quantitative yields (with Cu(II) as the limiting reagent) and selectivity combined with turnover numbers >800. Our report details mechanistic studies of this catalytic process using a combined experimental and computational approach. Examining catalysis with the complex ( Fl DAB)Rh(OAc)(η 2 -C 2 H 4 ) shows that the reaction rate has a dependence on catalyst concentration between first- and half-order that varies with both temperature and ethylene concentration, a first-order dependence on ethylene concentration with saturation at higher concentrations of ethylene, and a zero-order dependence on the concentration of Cu(II) oxidant. The kinetic isotope effect was found to vary linearly with the order in ( Fl DAB)Rh(OAc)(η 2 -C 2 H 4 ), exhibiting no KIE when [Rh] was in the half-order regime, and a k H / k D value of 6.7(6) when [Rh] was in the first-order regime. From these combined experimental and computational studies, competing pathways, which involve all monomeric Rh intermediates and a binuclear Rh intermediate in the other case, are presented.

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