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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Nitrogen Atom Transfer Catalysis by Metallonitrene C−H Insertion: Photocatalytic Amidation of Aldehydes

Abstract C−H amination and amidation by catalytic nitrene transfer are well‐established and typically proceed via electrophilic attack of nitrenoid intermediates. In contrast, the insertion of (formal) terminal nitride ligands into C−H bonds is much less developed and catalytic nitrogen atom transfer remains unknown. We here report the synthesis of a formal terminal nitride complex of palladium. Photocrystallographic, magnetic, and computational characterization support the assignment as an authentic metallonitrene (Pd−N) with a diradical nitrogen ligand that is singly bonded to Pd II . Despite the subvalent nitrene character, selective C−H insertion with aldehydes follows nucleophilic selectivity. Transamidation of the benzamide product is enabled by reaction with N 3 SiMe 3 . Based on these results, a photocatalytic protocol for aldehyde C−H trimethylsilylamidation was developed that exhibits inverted, nucleophilic selectivity as compared to typical nitrene transfer catalysis. This first example of catalytic C−H nitrogen atom transfer offers facile access to primary amides after deprotection.

Schmidt‐Räntsch, Till↗
DOE OSTI2016

Highly Efficient Cooperative Catalysis by Co III (Porphyrin) Pairs in Interpenetrating Metal-Organic Frameworks

A series of porous twofold interpenetrated In-Co III (porphyrin) metal–organic frameworks (MOFs) were constructed by in situ metalation of porphyrin bridging ligands and used as efficient cooperative catalysts for the hydration of terminal alkynes. The twofold interpenetrating structure brings adjacent Co III (porphyrins) in the two networks parallel to each other with a distance of about 8.8 Å, an ideal distance for the simultaneous activation of both substrates in alkyne hydration reactions. As a result, the In-Co III (porphyrin) MOFs exhibit much higher (up to 38 times) catalytic activity than either homogeneous catalysts or MOF controls with isolated Co III (porphyrin) centers, thus highlighting the potential application of MOFs in cooperative catalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Correlation between Chiral Modifier Adsorption and Enantioselectivity in Hydrogenation Catalysis

Infrared absorption spectroscopy performed in situ at the solid–liquid interface revealed that the adsorption on platinum supported catalysts of 1-(1-naphthyl)-ethylamine, which is used as a chiral modifier in hydrogenation catalysis, occurs through the amine group, not the aromatic ring as is widely believed. In this work, comparisons were performed against a set of related modifier compounds with targeted substitutions to help identify the key moiety involved in the adsorption. It was determined that neither naphthalene-based modifiers without amine groups nor those with tertiary amine moieties are capable of adsorbing on the metal surface to any significant extent. A direct correlation was also found between the ability of the amines to adsorb on the platinum surface and their performance as chiral modifiers that impart enantioselectivity to the hydrogenation of α-keto esters such as ethyl pyruvate.

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

Regioselective Arene C−H Alkylation Enabled by Organic Photoredox Catalysis

Abstract Expanding the toolbox of C−H functionalization reactions applicable to the late‐stage modification of complex molecules is of interest in medicinal chemistry, wherein the preparation of structural variants of known pharmacophores is a key strategy for drug development. One manifold for the functionalization of aromatic molecules utilizes diazo compounds and a transition‐metal catalyst to generate a metallocarbene species, which is capable of direct insertion into an aromatic C−H bond. However, these high‐energy intermediates can often require directing groups or a large excess of substrate to achieve efficient and selective reactivity. Herein, we report that arene cation radicals generated by organic photoredox catalysis engage in formal C−H functionalization reactions with diazoacetate derivatives, furnishing sp 2 –sp 3 coupled products with moderate‐to‐good regioselectivity. In contrast to previous methods utilizing metallocarbene intermediates, this transformation does not proceed via a carbene intermediate, nor does it require the presence of a transition‐metal catalyst.

Holmberg‐Douglas, Natalie↗
DOE OSTI2021

Enhanced Catalysis under 2D Silica: A CO Oxidation Study

Abstract Interfacially confined microenvironments have recently gained attention in catalysis, as they can be used to modulate reaction chemistry. The emergence of a 2D nanospace at the interface between a 2D material and its support can promote varying kinetic and energetic schemes based on molecular level confinement effects imposed in this reduced volume. We report on the use of a 2D oxide cover, bilayer silica, on catalytically active Pd(111) undergoing the CO oxidation reaction. We “uncover” mechanistic insights about the structure–activity relationship with and without a 2D silica overlayer using in situ IR and X‐ray spectroscopy and mass spectrometry methods. We find that the CO oxidation reaction on Pd(111) benefits from confinement effects imposed on surface adsorbates under 2D silica. This interaction results in a lower and more dispersed coverage of CO adsorbates with restricted CO adsorption geometries, which promote oxygen adsorption and lay the foundation for the formation of a reactive surface oxide that produces higher CO 2 formation rates than Pd alone.

Eads, Calley N.↗
DOE OSTI2022

Nitrogen Atom Transfer Catalysis by Metallonitrene C−H Insertion: Photocatalytic Amidation of Aldehydes

Abstract C−H amination and amidation by catalytic nitrene transfer are well‐established and typically proceed via electrophilic attack of nitrenoid intermediates. In contrast, the insertion of (formal) terminal nitride ligands into C−H bonds is much less developed and catalytic nitrogen atom transfer remains unknown. We here report the synthesis of a formal terminal nitride complex of palladium. Photocrystallographic, magnetic, and computational characterization support the assignment as an authentic metallonitrene (Pd−N) with a diradical nitrogen ligand that is singly bonded to Pd II . Despite the subvalent nitrene character, selective C−H insertion with aldehydes follows nucleophilic selectivity. Transamidation of the benzamide product is enabled by reaction with N 3 SiMe 3 . Based on these results, a photocatalytic protocol for aldehyde C−H trimethylsilylamidation was developed that exhibits inverted, nucleophilic selectivity as compared to typical nitrene transfer catalysis. This first example of catalytic C−H nitrogen atom transfer offers facile access to primary amides after deprotection.

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

Copper-Cobalt-Cerium Ternary Oxide as an Additive to a Conventional Platinum-Group-Metal Catalyst for Automotive Exhaust Catalysis

Recently, we reported on a ternary mixed-oxide catalyst that showed low-temperature CO oxidation activity under lean exhaust conditions without inhibition by hydrocarbons such as propene. However, the hydrocarbon oxidation activity of this Cu–Co–Ce (CCC) catalyst cannot be considered as a stand-alone solution to low-temperature automotive exhaust catalysis. To achieve both low-temperature oxidation of pollutants and a reduction in the total platinum-group-metal (PGM) content, we examined a 50 % physical mixture of traditional Pt/Al 2 O 3 and our CCC catalyst in two simulated exhaust protocols. Using this physical mixture, we were able to obtain equivalent or better hydrocarbon activity than the baseline Pt/Al 2 O 3 catalyst with half the total PGM content as well as increased sulfur tolerance for the CCC component of the mixture. Diffuse reflectance infrared Fourier transform spectroscopy data confirmed that despite exposure of sulfur-sensitive CCC to SO 2 , Cu + -carbonyl binding sites could still be seen if the catalyst was mixed with Pt/Al 2 O 3 .

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

Ionic Liquid Sheath Stabilizes Atomically Dispersed Reduced Graphene Aerogel‐Supported Iridium Complexes during Ethylene Hydrogenation Catalysis

Abstract An atomically dispersed reduced graphene aerogel (rGA)‐supported iridium catalyst having reactive ethylene ligands was synthesized at an iridium loading of 9.9 wt % and coated with an ionic liquid, 1‐ethyl‐3‐methylimidazolium acetate ([EMIM][OAc]). Continuous‐scan X‐ray absorption spectra demonstrated that the iridium remained site‐isolated in flowing equimolar C 2 H 4 and H 2 during a temperature ramp to 100 °C. The data further showed the lack of detectable iridium aggregation when the feed was H 2 ‐rich or even pure H 2 at 100 °C. An Arrhenius plot determined for ethylene hydrogenation catalysis with the sample in flowing equimolar ethylene and hydrogen showed no variation in the apparent activation energy at temperatures up to 100 °C, confirming that the active sites remained intact at the higher temperatures. The results point to opportunities for overcoming the stability limitations of atomically dispersed supported noble metal catalysts by choice of electron‐donor supports and ionic liquid sheaths.

Kurtoğlu‐Öztulum, Samira F.↗
DOE OSTI2024

Bifunctional Metal‐Organic Nanoballs Featuring Lewis Acidic and Basic Sites as a New Platform for One‐Pot Tandem Catalysis

Abstract The design and synthesis of polyhedra using coordination‐driven self‐assembly has been an intriguing research area for synthetic chemists. Metal‐organic polyhedra are a class of intricate molecular architectures that have garnered significant attention in the literature due to their diverse structures and potential applications. Hereby, we reportCu‐MOP, a bifunctional metal‐organic cuboctahedra built using 2,6‐dimethylpyridine‐3,5‐dicarboxylic acid and copper acetate at room temperature. The presence of both Lewis basic pyridine groups and Lewis acidic copper sites imparts catalytic activity to Cu‐MOP for the tandem one‐pot deacetalization‐Knoevenagel/Henry reactions. The effect of solvent system and time duration on the yields of the reactions was studied, and the results illustrate the promising potential of these metal‐organic cuboctahedra, also known as nanoballs for applications in catalysis.

Chemistry↗
DOE OSTI2019

Catalytic One‐Pot Conversion of Renewable Platform Chemicals to Hydrocarbon and Ether Biofuels through Tandem Hf(OTf) 4 +Pd/C Catalysis

Abstract Efficient conversion of renewable biomass platform chemicals into high‐quality fuels remains challenging. A one‐pot catalytic approach has been developed to synthesize various structurally defined biofuels by using Hf(OTf) 4 and Pd/C for selective tandem catalysis and 2‐methylfuran (2‐MF) as a renewable feedstock. 2‐MF first undergoes Lewis acid‐catalyzed hydroxyalkylation/alkylation (HAA) condensation with carbonyl compounds to afford intermediates containing the targeted carbon skeletons of hydrocarbon or ether products, and these intermediates then undergo hydrogenation or hydrodeoxygenation to afford the target products, catalyzed by metal triflate+Pd/C in the same pot. The present process can produce structurally defined alkanes and cyclic ethers under mild conditions.

Liu, Dong‐Huang↗
DOE OSTI2021

Tuning Ligand–Coordinated Single Metal Atoms on TiO 2 and their Dynamic Response during Hydrogenation Catalysis

Ligand-coordinated supported catalysts (LCSCs) are of growing interest for heterogeneous single-atom catalysis. Here, the effect of the choice of organic ligand on the activity and stability of TiO 2 -supported single-atom Pt-ligand catalysts was investigated for ethylene hydrogenation. The activity of these catalysts showed a significant dependence on the choice of ligand and also correlated with coordination number for Pt-ligand and Pt-Cl - . Of the three ligands examined in this study, the one with the lowest Pt coordination number, 1,10-phenanthroline-5,6-dione (PDO), showed the lowest reaction temperature and highest reaction rate, likely due to those metal sites being more accessible to reactant adsorption. In-situ X-ray absorption spectroscopy (XAS) experiments showed that the activity also correlated with good heterolytic dissociation of hydrogen, which was supported by OH/OD exchange experiments and was the rate-determining step of the hydrogenation reaction. In these in-situ XAS experiments up to 190 degrees C, the supported Pt-ligand catalyst showed excellent stability against structural and chemical change. Instead of Pt, the PDO ligand could be coordinated with Ir on TiO 2 to form Ir LCSCs that showed slow activation by loss of Ir-Cl bonds, then excellent stability in the hydrogenation of ethylene. Furthermore, these results provide the chance to engineer ligand-coordinated supported catalysts at the single-atom catalyst level by the choice of ligand and enable new applications at relatively high temperature.

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

Synthesis and dilute solution properties of branched poly(benzyl methacrylate) using na‐clay supported aqueous‐phase catalysis

ABSTRACT The supported aqueous‐phase catalysis (SAPC) using hydrated interface has been used to synthesize branched polymers (star and graft) of benzyl methacrylate (BnMA) via atom‐transfer radical polymerization (ATRP) in the presence of Na‐clay supported catalyst in anisole at ambient temperature. The propagation of star poly(BnMA)s using diPENDTA‐Br 6 , as hexa ‐functional initiator is confined at the hydrated interface between the support and the liquid medium as evident from the obtained polymers that are catalyst contamination‐free, and exhibited moderately narrow molecular weight distributions ( M w / M n ≤ 1.33). The hexa ‐functionality of synthesized stars is verified by 1 H NMR, the measurement of their intrinsic viscosity ([ η ]), and radius of gyration ( R g ). The polymerization was also recycled up to 5 times to produce star PBnMAs with high initiator efficiency. The star polymers prepared using hydrated Na‐clay supported is compared with star prepared using covalent silica supported catalyst system. The star polymer obtained from covalently supported catalyst gave broad M w / M n and poor initiator efficiency. The polystyrene‐ graft ‐PBnMA (PS‐ g ‐PBnMA) copolymer is also prepared using hydrated Na‐clay supported catalyst system in anisole at ambient temperature. The graft ‐copolymer had narrow M w / M n and was confirmed using 1 H NMR and atomic force microscopy. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56 , 2225–2237

Aggarwal, Ravi↗
DOE OSTI2017

Tailoring N-Terminated Defective Edges of Porous Boron Nitride for Enhanced Aerobic Catalysis

Tailoring terminated edge of hexagonal boron nitride (h–BN) for enhancing catalysis has turned to be an imperative for the rational design of a highly active aerobic catalyst. Herein, a tailoring N–terminated porous BN (P–BN) strategy is reported with a zinc (Zn) salt as a dual–functional template. The Zn salt acts as both an in situ template and an N–terminated defective edges directing agent. The zinc salt template turns to Zn nanoparticles (Zn NPs) and functions as physical spacers, which are subsequently removed at a higher temperature, for producing P–BN, whose high surface area is high to 1579 m 2 g –1 . Moreover, because of the lower electronegativity of Zn, boron (B) atoms are partly replaced by Zn atoms and ultimately preferred to N–terminated edges with the volatilization of Zn NPs. Owing to the moderate dissociative energy of oxygen atoms on N–terminated edges, the N–terminated edges are proved to be the origin of an enhanced aerobic catalytic activity by density functional theory (DFT) calculations. Furthermore, the DFT calculation result is experimentally verified.

2D↗
DOE OSTI2023

Plant-wide modeling and techno-economic analysis of a direct non-oxidative methane dehydroaromatization process via conventional and microwave-assisted catalysis

Direct non-oxidative methane dehydroaromatization (DHA) process via conventional and microwave (MW)-assisted thermo-catalytic catalysis is studied. Rate models for methane DHA reactions, including the effect of catalyst deactivation, are developed by using the in-house experimental data. Model results for gas concentration profile and catalyst deactivation are in good agreement with the experimental data. This rate model is then used for the development of dynamic multi-scale, multi-physics commercial-scale reactor models. Total number of fixed bed reactors desired for a cyclic steady state process is estimated. Plant-wide models are then developed for conventional and MW-assisted processes for producing products of desired specifications. Techno-economic analysis of the methane DHA process is undertaken. Economics of these methane DHA processes are compared with the typical multi-step natural gas to aromatics production process via methanol synthesis. Sensitivity of internal rate of return (IRR) and net present value (NPV) to various economic and process parameters such as plant scale, desired rate of return, reactor cost, feedstock and utility cost, catalyst variable cost, and MW reactor cost is studied. Here, electric equivalent efficiency of the conventional methane DHA process is found to be 69.2 % and 67.3 % at 750 °C and 800 °C, respectively, while the MW-assisted methane DHA process has the electric equivalent efficiency of 48.9 % at 800 °C. IRRs of the conventional methane DHA process at 750 °C and 800 °C, and MW-assisted process are 15.2 %, 17.5 %, and 18.8 %, respectively for a methane feed flowrate of 19,782 kg/h, while the IRR of the multi-step natural gas to aromatics production process is estimated to be 0 % for the same plant scale. Impact of change in the methane price, electricity price, and catalyst cost is found to be considerable on the process economics, while the cost of the MW reactor is found to have negligible impact.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Computational catalyst screening: Scaling, bond-order and catalysis

Here, the design of new and better heterogeneous catalysts needed to accommodate the growing demand for energy from renewable sources is an important challenge for coming generations. Most surface catalyzed processes involve a large number of complex reaction networks and the energetics ultimately defines the turn-over-frequency and the selectivity of the process. In order not to get lost in the large quantities of data, simplification schemes that still contain the key elements of the reaction are required. Adsorption and transition state scaling relations constitutes such a scheme that not only maps the reaction relevant information in terms of few parameters but also provides an efficient way of screening for new materials in a continuous multi-dimensional energy space. As with all relations they impose certain restrictions on what can be achieved and in this paper, I show why these limitations exist and how we can change the behavior through an energy-resolved approach that still maintains the screening capabilities needed in computational catalysis.

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

In situ visualisation of zeolite anisotropic framework flexibility during catalysis

Zeolites exhibit framework flexibility driving their chemical and catalytic properties. Since the zeolitic pores are extremely small, a slight strain generated in the crystal induces compelling changes in shape, connectivity, accessibility, and the framework chemical properties. These modifications affected the adsorption and desorption of reactants/products and the diffusion within the channels during reaction. Using in situ 3D Bragg coherent X-ray diffraction imaging, we unveil the dynamics of the zeolite structure during catalysis, contraction and/or expansion of its framework also known as zeolite framework flexibility. Here, we imaged three-dimensionally a single faujasite zeolite crystal during the ethanol dehydration reaction revealing anisotropic lattice dynamics simultaneously to guest molecules formation. Understanding zeolite flexibility could permit to tune zeolites properties towards potentially higher adsorption and selectivity.

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

Phenylene-linked tetrapyrrole arrays containing free base and diverse metal chelate forms – Versatile synthetic architectures for catalysis and artificial photosynthesis

Tetrapyrrole macrocycles are central to photosynthesis yet a single macrocycle does not carry out photosynthesis; rather, assemblies of tetrapyrrole macrocycles work in concert in antenna complexes, reaction centers, and electron-transport chains to harvest sunlight, funnel excited-state energy and separate charge for biological use. A longstanding theme in artificial photosynthesis has been to construct covalently linked “arrays” of metalated and free base tetrapyrrole macrocycles for fundamental studies of such processes, which entail excited-state and ground-state interactions. Among linkers in arrays chemistry, the 1,2-, 1,3-, or 1,4-disubstituted phenylene unit has proved very attractive owing to the resulting short distance, defined architecture, and appropriate extent of electronic coupling of adjacent macrocycles to give rapid electron and/or energy transfer while largely retaining desired spectral features. Eight distinct strategies to construct phenylene-linked tetrapyrrole arrays are identified in a review with comprehensive coverage since inception in the early 1970s through mid-year 2021. The arrays predominantly incorporate porphyrins with very few chlorins and bacteriochlorins, reflecting historic availability of synthetic methods for macrocycle formation. Of the eight strategies, only two appear applicable to (bacterio)chlorins. While studies in artificial photosynthesis have largely fueled this field, applications in catalysis have also been examined. Altogether >400 arrays are covered. The review delves into synthesis and molecular design, sketches photophysical properties, and suggests unrealized opportunities in arrays chemistry.

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