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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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Nanostructured carbon electrocatalyst supports for intermediate-temperature fuel cells: Single-walled versus multi-walled structures

It is unknown if nanostructured carbons possess the requisite electrochemical stability to be used as catalyst supports in the cathode of intermediate-temperature solid acid fuel cells (SAFCs) based on the CsH2PO4 electrolyte. To investigate this application, single-walled carbon nanohorns (SWNHs) and multi-walled carbon nanotubes (MWNTs) were used as supports for Pt catalysts in SAFCs operating at 250 °C. SWNH-based cathodes display greater maximum activity than their MWNT-based counterparts at a cell voltage of 0.8 V, but are unstable in the SAFC cathode as a consequence of electrochemical carbon corrosion. MWNT-based cells are resistant to this effect and capable of operation for at least 160 h at 0.6 V and 250 °C. Cells fabricated with nanostructured carbon supports are more active (52 mA cm -1 vs. 28 mA cm -1 at 0.8 V) than state-of-the-art carbon-free formulations while simultaneously displaying enhanced Pt utilization (40 mA mgPt -1 vs. 16 mA mgPt -1 at 0.8 V). Finally, these results suggest that MWNTs are a viable support material for developing stable, high-performance, low-cost air electrodes for solid-state electrochemical devices operating above 230 °C.

25 ENERGY STORAGE↗
DOE OSTI2011

TPR investigations on the reducibility of Cu supported on Al{sub 2}O{sub 3}, zeolite Y and SAPO-5

Reducibility of Cu supported on Al{sub 2}O{sub 3}, zeolite Y and silicoaluminophosphate SAPO-5 has been investigated in dependence on the Cu content using a method combining conventional temperature programmed reduction (TPR) by hydrogen with reoxidation in N{sub 2}O followed by a second the so-called surface-TPR (s-TPR). The method enables discrimination and a quantitative estimation of the Cu oxidation states +2, +1 and 0. The quantitative results show that the initial oxidation state of Cu after calcination in air at 400 deg. C, independent on the nature of the support, is predominantly +2. Cu{sup 2+} supported on Al{sub 2}O{sub 3} is quantitatively reduced by hydrogen to metallic Cu{sup 0}. Comparing the TPR of the samples calcined in air and that of samples additionally pre-treated in argon reveals that in zeolite Y and SAPO-5 Cu{sup 2+} cations are stabilized as weakly and strongly forms. In both systems, strongly stabilized Cu{sup 2+} ions are not auto-reduced by pre-treatment in argon at 650 deg. C, but are reduced in hydrogen to form Cu{sup +}. The weakly stabilized Cu{sup 2+} ions, in contrast, may be auto-reduced by pre-treatment in argon at 650 deg. C forming Cu{sup +} but are reduced in hydrogen to metallic Cu{sup 0}. - Graphical Abstract: TPR, TPR-(act), s-TPR and s-TPR-(act) profiles of (1.36)Cu/SAPO-5 (A), (4.55)Cu/SAPO-5 (B) and (9.19)Cu/SAPO-5 (C) samples. The intensities of TCD signals in (A) and (B) are multiplied by 4.5 and 2, respectively. Highlights: > Cu supported on SAPO-5, alumina and zeolite Y was investigated by TPR and s-TPR. > Cu oxidation states can be discriminated and quantitatively determined. > In zeolite Y and SAPO-5 Cu{sup 2+} cations are stabilized at weak and strong forms. > Strongly stabilized Cu{sup 2+} cannot be auto-reduced in argon at 650 deg. C.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Dispersion states and acid properties of SiO{sub 2}-supported Nb{sub 2}O{sub 5}

Nb{sub 2}O{sub 5}/SiO{sub 2} samples were prepared by the incipient-wetness impregnation method using niobium oxalate aqueous solution. The microstructure and dispersion process of the niobia species supported on SiO{sub 2} were characterized by means of power X-ray diffraction (XRD), laser Raman spectroscopy (LRS), and UV–vis diffuse reflectance spectroscopy (UV–vis DRS). The acid properties were investigated by the method of Hammett indicator and Pyridine adsorption infrared (Py-IR) spectroscopy. The results showed that the dispersion process of Nb{sub 2}O{sub 5} was performed by consuming surface hydroxyl groups of the amorphous SiO{sub 2} support. The aggregation of niobia species led to the formation of microcrystalline particles, so that there was no a clear monolayer dispersion capacity for Nb{sub 2}O{sub 5} supported on amorphous SiO{sub 2}. Furthermore, the catalytic activities of the as-prepared samples were evaluated by the condensation reaction of iso-butene (IB) and iso-butyraldehyde (IBA) to form 2,5-dimethyl-2,4-hexadiene (DMHD). The catalytic activities of the as-prepared samples for the condensation and their acid properties were strongly affected by the dispersion states. - Graphical abstract: The acid amount and strength of Nb{sub 2}O{sub 5}/SiO{sub 2} samples varied with the increase of Nb{sub 2}O{sub 5} loading. The catalytic activities of the as-prepared samples for the condensation and their acid properties were strongly affected by the dispersion states. - Highlights: • The dispersed process of Nb{sub 2}O{sub 5} was completed by consuming surface hydroxyl groups of SiO{sub 2}. • XRD quantitative phase analysis is not applicable for oxides dispersing on amorphous support. • The catalytic activity of Nb{sub 2}O{sub 5}/SiO{sub 2} is closely related to the dispersion state of SiO{sub 2}.

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

Ligand-tailored single-site silica supported titanium catalysts: Synthesis, characterization and towards cyanosilylation reaction

A successive anchoring of Ti(NMe{sub 2}){sub 4}, cyclopentadiene and a O-donor ligand, 1-hydroxyethylbenzene (PEA), 1,1′-bi-2-naphthol (Binol) or 2,3-dihydroxybutanedioic acid diethyl ester (Tartrate), on silica was conducted by SOMC strategy in moderate conditions. The silica, monitored by in-situ Fourier transform infrared spectroscopy (in-situ FT-IR), was pretreated at different temperatures (200, 500 and 800 °C). The ligand tailored silica-supported titanium complexes were characterized by in-situ FT-IR, {sup 13}C CP MAS-NMR, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) and elemental analysis in detail, verifying that the surface titanium species are single sited. The catalytic activity of the ligand tailored single-site silica supported titanium complexes was evaluated by a cyanosilylation of benzaldehyde. The results showed that the catalytic activity is dependent strongly on the dehydroxylation temperatures of silica and the configuration of the ligands. - Graphical abstract: The ligand-tailored silica supported “single site” titanium complexes were synthesized by SOMC strategy and fully characterized. Their catalytic activity were evaluated by benzaldehyde silylcyanation. - Highlights: • Single-site silica supported Ti active species was prepared by SOMC technique. • O-donor ligand tailored Ti surface species was synthesized. • The surface species was characterized by XPS, {sup 13}C CP-MAS NMR, XANES etc. • Catalytic activity of the Ti active species in silylcyanation reaction was evaluated.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Characterization of supported TiO{sub 2}-based catalysts green-prepared and employed for photodegradation of malodorous DMDS

Graphical abstract: Display Omitted Highlights: ► We prepare rutile-TiO{sub 2} based catalysts using a simple and eco-efficient method. ► TiO{sub 2} based catalysts coated on supporting materials have large BET surface areas. ► Supported TiO{sub 2} based catalysts efficiently degrade malodorous DMDS. -- Abstract: Titanium dioxide (TiO{sub 2})-based catalysts coated onto two supporting materials (Pyrex glass beads and porous polypropylene fibers) in laboratory have been prepared and characterized. A modified preparation process at low temperature involving the addition of distilled water, aqueous ammonia, and ferrous sulfate, respectively, was used to enhance the spontaneous precipitation of three TiO{sub 2}-based catalysts. The Brunauer–Emmett–Teller surface area of three catalysts was ranged from 160.1 to 202.7 m{sup 2}/g. The surface morphology of three catalysts was identified by a scanning electron microscopy equipped with an X-ray energy dispersive spectrometer. The photocatalytic degradation of dimethyldisulfide was investigated using the supported TiO{sub 2}-based catalysts. The original dimethyldisulfide almost was degraded within 2 h. A similar photocatalytic activity on degrading dimethyldisulfide was demonstrated in comparison with commercial catalysts. Simplicity, low cost, low energy consumption, and solvent-free are the advantages of this proposed method which can be used to photodecompose environmental organic pollutants effectively without heat treatment.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Facile morphology controllable synthesis of PtPd nanorods on graphene-multiwalled carbon nanotube hybrid support as efficient electrocatalysts for oxygen reduction reaction

Highlights: • G–M hybrid was prepared by a novel modified Hummers method followed by thermal annealing. • G–M was verified to be more efficient as the electrocatalyst support compared with G. • Ultrathin PtPd alloy nanorods were supported on the G–M hybrid. • The electrochemical activity of PtPd NRs/G–M outperforms the commercial Pt/C. - Abstract: One-dimensional (1D) anisotropic platinum-based nanorods are particularly attractive electrocatalysts for oxygen reduction reaction (ORR) owing to the inherent structural advantages. In this work, we report the growth of ultrathin PtPd alloy nanorods (3–4 nm) on Graphene-Multiwalled carbon nanotube (G–M) hybrid support via a facile surfactant-free and template-free method as the efficient electrocatalyst for ORR. The as-synthesized PtPd NRs/G–M catalyst exhibits more excellent activity and better durability toward ORR than Pt NRs/G and Pt NRs/G–M catalysts. Noteworthily, it shows an outstanding half-wave potential of 0.810 V and mass activity of 49.5 mA mg{sup –1} at 0.85 V, which are 30 mV and 2.1 times higher than those of commercial 40 wt% Pt/C (JM40) catalyst, respectively. After the accelerated durability tests (ADTs), it also maintains superior stability than JM40. The superior performance is attributed to the combination of the advantageous 1D morphological motif and the synergistic effect with G–M support.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Syntheses of gold supported on metal oxides and their application in organic transformations

Herein, we report a general and straightforward synthesis method for gold supported on mesoporous and microporous metal oxides. Supported materials, in general, show higher crystallinity compare to unsupported systems as verified through powder X-ray diffraction (XRD). Also, through XRD, most of the metal is observed to be in its oxide form, whereas the gold support was found to be in its metallic state, which has been further confirmed from TEM. In terms of surface area, the catalyst was not found to follow any trend. Morphology wise, there are no changes observed after doping except in few cases. Combined results from XRD, X-ray fluorescence spectroscopy, Auger, and X-ray photoelectron spectroscopy suggest that gold is mainly in the bulk and very little (0.04% in case of gold doped calcium oxide) or non (in case of gold doped mixed manganese-cerium oxide) on the surface. The presence of Au (0) 4f peaks in XPS further confirms the metallic state of the gold. Oxides of indium, magnesium and calcium have been studied for the organic transformation reactions. An enhancement in activity and product selectivity was observed in the case of the gold supported catalysts. Indium serves as a great catalyst for C–C coupling and electrophilic aromatic substitution reactions and gives >99% conversion. Interestingly, 88% selectivity for C–C coupling and >99% selectivity for aromatic substitution have been achieved at 100 °C and room temperature respectively. Magnesium and calcium give Knoevenagel condensation products. At room temperature with very low catalyst loading, >99% conversion and selectivity were observed for the Knoevenagel reaction with as high as 35.30 TOF. Finally, a mechanism for the C–C coupling reaction has been proposed based on these results.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Water-gas shift reaction on alumina-supported Pt-CeO x catalysts prepared by supercritical fluid deposition

Alumina-supported platinum catalysts, both with and without ceria, were prepared by supercritical fluid deposition and evaluated for activity for water-gas shift reaction. The organometallic precursor, platinum(II) acetylacetonate, was deposited from solution in supercritical carbon dioxide. Analysis of the catalysts by high resolution scanning transmission electron microscopy indicated that platinum was present in the form of highly dispersed metal nanoparticles. Pretreatment of the alumina-supported ceria in hydrogen prior to the deposition of the platinum precursor resulted in more platinum nucleated on ceria than non-pretreated alumina-supported ceria but varied in both particle size and structure. The ceria-containing catalyst that was not pretreated exhibited a more uniform particle size, and the Pt particles were encapsulated in crystalline ceria. Reaction rate measurements showed that the catalyst was more active for water-gas shift, with reaction rates per mass of platinum that exceeded most literature values for water-gas shift reaction on Pt-CeO x catalysts. The high activity was attributed to the significant fraction of platinum/ceria interfacial contact. We found that these results show the promise of supercritical fluid deposition as a scalable means of synthesizing highly active supported metal catalysts that offer efficient utilization of precious metals.

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

Impact of different catalysis supported by oyster shells on the pyrolysis of tyre wastes in a single and a double fixed bed reactor

Highlights: • An innovative way in the disposal of tyre wastes with energy recovery by pyrolysis is proposed. • Performance of catalysts is improved by spreading them over layers of oyster shells. • One or two levels of supported catalytic beds may favor the quantity and/or the calorific value of the pyrolysis by-products. - Abstract: The treatment and disposal of tyres from vehicles has long been of considerable environmental importance. Studies have been undertaken to reduce their environmental impact. In this study, an alternative gas was produced from automobile tyre wastes by the means of a controlled pyrolysis. To do so, a novel catalytic system was designed with the aim of increasing the rate of conversion and improving the quality of the pyrolysis products. This work aimed also to reduce the severity of the overall reactions, by using powder catalysts (MgO, Al{sub 2}O{sub 3}, CaCO{sub 3}, and zeolite ZSM-5) uniformly distributed on two layers of oyster shells (OS) particles. The catalyst/tyres mass ratio was kept for all the tests at 1/30. The pyrolysis reactor was maintained at 500 °C and the influence of each catalyst and of the number of shell beds (0, 1 or 2), on the yield and composition of the derived products, was examined. The gas yields could contribute by 1.2% of total consumption in Tunisia. Furthermore, some combinations could upgrade the derived gas and made it possible to use it as such or with the minimum of post-treatment. It was found that, with the use of supported catalyst, the gas produced is 45% greater compared to classical thermal pyrolysis. The Heating value of the produced gas was also improved by the use of supported catalysts; it was found 16% greater with the use of Al{sub 2}O{sub 3}/OS compared to non-catalytic pyrolysis. When compared to the gas obtained from only one catalytic supported bed, the sulfur content was reduced by 80% with the use of CaCO{sub 3}/OS on two catalytic beds.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2026

Regioselective Hydrosilylation Catalysis with Supported Well-Defined Pt(0) Complexes: Effects of Surface Anions and Phosphenium Ligands

Achieving stable, selective single-atom catalysts is challenging because localsurface-site structures are difficult to control. Surface organometallic chemistry and organic−inorganic hybrid materials offer partial solutions, but applications to supporting zero-valent metals are limited. We demonstrate that well-defined, ionically bound N-heterocyclic phosphenium ([NHP] + ) ligands can be generated on silylium-functionalized sulfated zirconia ([ i Pr 3 Si][SZO]). These surface-bound [NHP][SZO] ligands coordinate Pt(0) centers, forming [(NHP)Pt(0)L][SZO] precatalysts that are highly active for alkyne hydrosilylation. Systematic studies reveal that sterically bulky aromatic ligands enhance regioselectivity, achieving performances comparable to molecular Pt catalysts. Further, more-coordinating anions support more-regioselective precatalysts; therefore, SZO supports more-selective species than weaker-coordinating Al(OC(CF 3 ) 3 ) 3 - functionalized silica, a trend confirmed by molecular analogues. These results demonstrate that both the ligand and support control catalytic behavior and enable solid-state structure− activity relationships.

Catalysts↗
DOE OSTI2021

Impact of Hydration on Supported V 2 O 5 /TiO 2 Catalysts as Explored by Magnetic Resonance Spectroscopy

Supported vanadium oxide catalysts are important industrial materials for a wide array of chemical transformations. The condition of surface hydration is of particular interest as a reflection of the state of a freshly manufactured catalysts prior to its activation in catalytic reactors or under conditions of photocatalysis where surface vandia are exposed to moisture. Under such conditions, the surface vanadia species undergo structural changes as evidenced by 51 V MAS NMR in this study. For low surface vanadia densities on titania, a modest trend towards the formation of dimeric and oligomeric vanadia species was observed under hydrated conditions when compared to the corresponding dehydrated catalyst, which contains a large abundance of monomeric vanadia species. The incorporation of tungsten oxide to the V 2 O 5 /TiO 2 catalyst with low surface vanadia density, however, is found to better stabilize the surface vanadia species on the titania support upon hydration than its tungsta-free counterpart. This stabilization is not an intrinsic property of more extensively oligomerized surface vanadia species in the presence of tungsten oxide, evidenced by conditions of high concentrations of surface vanadia oligomers on titania that exhibit dramatic structural changes upon hydration. At high surface vanadia coverage under hydrated environments, the simultaneous observation of crystalline V 2 O 5 nanoparticles and a mobile phase of surface vanadia species is apparent, where vanadia species are dissolved in the thin hydration layer on the titania support. These new findings have broad implications on the behavior of other metal oxide species on high surface oxide supports under hydrated conditions.

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

Single-Molecule Kinetics of Styrene Hydrogenation on Silica-Supported Vanadium: The Role of Disorder for Single-Atom Catalysts

We report a theoretical approach for the study of supported atom catalysis is developed based on recent advances in the study of single-molecule kinetics. This view is particularly useful in exhibiting the role of disorder in single-atom and single-site catalysts on amorphous supports. The distribution of passage times (or waiting times) through a complex catalytic network originating from a set of coupled active sites is described by a probability distribution function (PDF), f(t), that reflects the local environment of the reaction center. An efficient algorithm is developed based on the linear algebra of the Markov transition matrix that produces f(t) or its moments. The kinetics of the hydrogenation reaction of styrene on an organovanadium(III) catalyst supported on amorphous silica is studied. A kinetic model consisting of three intertwined catalytic cycles emanating from three chemically distinct active sites is proposed to describe the chemistry. Density functional theory (DFT) calculations are employed to determine the free energy barriers of the reactions, which are used to construct the rate coefficient matrix. The disorder induced by the amorphous support material is divided into a low-dimensional short-range component reflecting the covalent structures near the reaction center and a weaker long-range component modeling the bulk randomness. The results are computed and analyzed for a wide range of concentration values and disorder scenarios. The unusual structure in the f(t) PDF is found to occur for certain cases that reveal the contribution of multiple catalytic pathways acting in concert.

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

Role of Oxidizing Conditions in the Dispersion of Supported Platinum Nanoparticles Explored by Ab Initio Modeling

Achieving fine control over the dispersion of supported platinum nanoparticles (Pt) is a promising avenue to enhancing their catalytic activity and selectivity. Experimental observations suggest that exposing ceria-supported Pt nanoparticles to O 2 at 500 °C promotes their dispersion into smaller particles and eventually single atoms. The exact role of oxygen in this process is not yet well understood. Past density functional theory studies of ceria-supported Pt have typically narrowed their scope to single atoms and clusters of a few atoms. Herein, we combine several approaches and types of models in a consistent atomistic framework to evaluate the relative stability of ceria-supported Pt as a function of the degree of oxidation of Pt and of the particle size, ranging from single atoms to nanoparticles 1.5 nm of diameter. Finally, we find that the largest nanoparticles remain the thermodynamically most stable species on the lowest energy facet of ceria even under oxidizing conditions, suggesting that stronger adsorption sites are required to stabilize smaller clusters and single atoms and promote oxidative dispersion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Is There a Negative Thermal Expansion in Supported Metal Nanoparticles? An in Situ X-ray Absorption Study Coupled with Neural Network Analysis

Interactions with their support, adsorbates, and unique structural motifs are responsible for many intriguing properties and potential applications of supported metal nanoparticles (NPs). At the same time, they complicate the interpretation of experimental data. In fact, the methods and approaches that work well for the ex situ analysis of bulk materials may be inaccurate or introduce artifacts in the in situ analysis of nanomaterials. Here, we revisit the controversial topic of negative thermal expansion and anomalies in the Debye temperature reported for oxide-supported metal NPs. In situ X-ray absorption experimental data collected for Pt NPs in ultrahigh vacuum and an advanced data analysis approach based on an artificial neural network demonstrate that Pt NPs do not exhibit intrinsic negative thermal expansion. Similarly, as for bulk materials, in the absence of adsorbates and strong particle-support interaction, the bond lengths in metal NPs increase with temperature. Lastly, the previously reported anomalies in particle-size-dependent Debye temperatures can also be linked to the artifacts in the interpretation of conventional X-ray absorption data of disordered materials such as NPs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Diphosphine-Protected Au 22 Nanoclusters on Oxide Supports Are Active for Gas-Phase Catalysis without Ligand Removal

Investigation of monodispersed and atomically-precise Au nanoclusters provides a route to understand the roles of coordination, size, and ligand effects in Au catalysis. We have explored the catalytic behavior of a newly-synthesized Au 22 (L 8 ) 6 nanocluster (L = 1,8-bis(diphenylphosphino) octane) with in situ uncoordinated Au sites supported on TiO 2 , CeO 2 and Al 2 O 3 . Stability of the supported Au 22 nanoclusters was probed structurally by EXAFS and HAADF-STEM, and their adsorption and reactivity for CO oxidation were investigated by IR absorption spectroscopy and temperature programed flow reaction. Low temperature CO oxidation activity was observed for the supported pristine Au 22 (L 8 ) 6 nanoclusters without ligand removal. Isotopically labeled O 2 was used to demonstrate that the reaction pathway occurs through a redox mechanism, consistent with the observed support-dependent activity trend: CeO 2 > TiO 2 > Al 2 O 3 . Substantiated by density functional theory (DFT) calculations, we conclude that the uncoordinated Au sites in the intact Au 22 (L 8 ) 6 nanoclusters are capable of adsorbing CO, activating O2 and promoting CO oxidation reaction. Thanks to the presence of the in situ coordination unsaturated Au atoms, this work is the first clear demonstration of a ligand-protected Au nanocluster that are active for gas phase catalysis without the need of ligand removal.

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

Role of Polymer Architecture in CO 2 Capture from Air Using Supported Poly(alkylenimine)s: Linear vs Branched Polymers

Direct air capture (DAC) of CO 2 coupled with geologic storage is a promising climate change mitigation strategy, with some applications employing amines supported on porous solids as CO 2 sorbents. While branched poly(ethylenimine) (PEI) is the standard benchmark amine material, it suffers from limited oxidative stability. Poly(propylenimine) (PPI), as an alternative, has previously demonstrated improved resistance to degradation under harsh oxidative conditions. Linear and branched PEI are commercially available, though at different molecular weights, while PPI is not commercially available. For this reason, a comparative study of all four polymers (linear PEI, branched PEI, linear PPI, branched PPI) has not been reported for DAC. In this study, we synthesize and compare low-molecular-weight (∼800 g/mol) linear (L) and branched (B) PEI and PPI supported on a model support, SBA-15 silica. These materials are evaluated for CO 2 adsorption under dry, DAC-relevant conditions (400 ppm of CO 2 , 30 °C). LPPI exhibited the highest amine efficiency at all loadings, reaching a maximum of 0.14 mmol CO 2 /mmol N, outperforming BPEI, while LPEI consistently showed the lowest uptake capacity. Temperature-programmed desorption reveals that the structure of the amine polymer impacts the CO 2 binding strength, with branched polymers displaying higher desorption energies of 102−111 kJ/mol. In situ infrared spectroscopy experiments show that all sorbents preferentially capture CO 2 as ammonium carbamate. Isobaric CO 2 uptake studies further underscore the influence of polymer mobility and support pore crowding on performance, while demonstrating the sorbents’ performance at elevated temperatures and CO 2 concentrations. All materials demonstrated good stability over 25 adsorption−desorption cycles using thermal regeneration in an inert gas purge, with only BPPI displaying a 10−11% decrease in capacity/amine efficiency during cycling, possibly due to the loss of low molecular weight, oligomeric amines. This is the first side-by-side comparison of the CO 2 sorption properties of linear and branched PEI and PPI with similar molecular weights. These findings highlight the significant role of polymer architecture in CO 2 capture efficiency and inform future designs of durable, high-performance DAC sorbents.

adsorbents↗
DOE OSTI2022

Deciphering the Mechanistic Role of Individual Oxide Phases and Their Combinations in Supported Mn–Na 2 WO 4 Catalysts for Oxidative Coupling of Methane

Oxidative coupling of methane (OCM) is an attractive direct route for upgrading methane to valuable chemicals. In this study, Temporal Analysis of Products (TAP) and steady state experiments are conducted to understand the role of individual oxide phases and their combinations in supported Mn-Na 2 WO 4 /SiO 2 catalysts for OCM. The results from TAP transient kinetic studies indicate that Mn plays an important role in promoting gas phase oxygen activation, while NaO x /SiO 2 and WO x /SiO 2 are relatively inert towards gas phase oxygen and methane activation. However, the supported catalyst combining Na and W in the form Na 2 WO 4 show enhanced gas phase oxygen activation exhibiting a much lower oxygen activation energy (148 kJ/mol) and enhanced activity toward methane activation as compared to the individual supported oxide catalysts. Addition of Mn to Na 2 WO 4 /SiO 2 further decreases the oxygen activation energy by 40 kJ/mol. Moreover, methane activation is also enhanced with CH 3 as the main intermediate but, with increasing Mn content, more CH 2 intermediates are observed. Different forms of oxygen (both dioxygen and atomic) are detected on the catalyst surface using isotopic pump/probe pulsing and their distribution is found to depend on the catalyst composition. An optimal Mn content in the Na 2 WO 4 /SiO 2 catalyst system is needed to enhance the amount of dioxide surface species (e.g., superoxide 16 O 2 - or peroxide 16 O 2 2- ) associated with the Na 2 WO 4 leading to high C 2 selectivity for OCM. When the Mn content is too high, the larger MnOx domains are shown to contribute to the formation of higher concertation of monoxide surface species that lead to nonselective OCM pathways. This insight from transient kinetic characterization using TAP combined with conventional steady state studies, provides a deeper understanding of the role of individual oxide phases and their combination on supported catalysts toward the formation of intermediate surface species and their impact on the OCM reaction mechanism. This knowledge is critical toward designing superior catalyst formulations for OCM.

10 SYNTHETIC FUELS↗
DOE OSTI2015

Mesoporous Silica-Supported Amidozirconium-Catalyzed Carbonyl Hydroboration

The hydroboration of aldehydes and ketones using a silica-supported zirconium catalyst is reported. Reaction of Zr(NMe 2 ) 4 and mesoporous silica nanoparticles (MSN) provides the catalytic material Zr(NMe 2 ) n @MSN. Exhaustive characterization of Zr(NMe 2 ) n @MSN with solid-state (SS)NMR and infrared spectroscopy, as well as through reactivity studies, suggests its surface structure is primarily ≡SiOZr(NMe 2 ) 3 . The presence of these nitrogen-containing zirconium sites is supported by 15 N NMR spectroscopy, including natural abundance 15 N NMR measurements using dynamic nuclear polarization (DNP) SSNMR. The Zr(NMe 2 ) n @MSN material reacts with pinacolborane (HBpin) to provide Me 2 NBpin and the material ZrH/Bpin@MSN that is composed of interacting surface-bonded zirconium hydride and surface-bonded borane ≡SiOBpin moieties in an approximately 1:1 ratio, as well as zirconium sites coordinated by dimethylamine. The ZrH/Bpin@MSN is characterized by 1 H/ 2 H and 11 B SSNMR and infrared spectroscopy and through its reactivity with D 2 . The zirconium hydride material or the zirconium amide precursor Zr(NMe 2 ) n @MSN catalyzes the selective hydroboration of aldehydes and ketones with HBpin in the presence of functional groups that are often reduced under hydroboration conditions or are sensitive to metal hydrides, including olefins, alkynes, nitro groups, halides, and ethers. Remarkably, this catalytic material may be recycled without loss of activity at least eight times, and air-exposed materials are catalytically active. These supported zirconium centers are robust catalytic sites for carbonyl reduction and that surface-supported, catalytically reactive zirconium hydride may be generated from zirconium-amide or zirconium alkoxide sites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗