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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Hydrolysis Reaction Pathways of Thorium Oxide Nanoclusters

Density functional theory benchmarked by correlated molecular orbital theory is used to develop a fundamental and predictive understanding of the interaction of thorium oxide nanoclusters with gas phase water to provide insight into nuclear-waste storage, production of thorium nuclear reactor fuels, and reprocessing of spent fuel. The structures of Th n O 2n (n = 3 – 6) clusters and their interactions with water have been studied at the B3LYP, MP2, and CCSD(T) levels. Hydrolysis is initiated by the formation of Lewis acid-base adducts, with relative H 2 O binding energies (physisorption) ranging from −15 kcal/mol to −22 kcal/mol. The initial H 2 O physisorption energy is ca. −21 kcal/mol regardless of the cluster size and is consistent with the experimentally obtained initial adsorption energy on a thorium dioxide surface. The physisorption enthalpies for additional water molecules can be affected by the presence of terminal groups OH groups generated by proton transfer to a Th-O near the site of adsorption. The hydrolysis products (chemisorption) form either bridging or terminal hydroxides. More exothermic hydrolysis steps were predicted for the formation of terminal hydroxides as compared to the formation of bridging hydroxides. Here, the calculated transition state barriers for transfer of protons from bound water complexes to form the chemisorption products are very low. Overall, water readily reacts with thorium oxide clusters preferring hydroxide products over hydrated complexes. First and second order fits were predicted for the combined physisorption and chemisorption energies for the hydrolysis of thorium oxide clusters. Finally, ionization energies and electron affinities were calculated as were HOMO-LUMO gaps to provide additional insights into the properties of the thorium oxide and hydroxide clusters.

Adsorption↗
DOE OSTI2025

Ultrafast Correlation Energy Estimator

A virtually no-cost method is proposed that can compute the correlation energies of general, covalently bonded, organic, and inorganic molecules (including conjugated π-electron systems) with a well-defined dominant Lewis structure at the accuracy of 99.5% of the near-exact values determined by the coupled-cluster singles, doubles, and perturbative triples [CCSD(T)] in the complete-basis-set (CBS) limit. This Correlation Energy Per Bond (CEPB) method assigns a partial correlation energy to each bond type (characterized by the identities of the two atoms forming the bond and its integer bond order) and to a lone pair, regardless of the bond length, bond angle, sp-hybridization, π-electron conjugation, ionicity, noncovalent interactions, etc. At its current stage, the method is mainly suitable for near-equilibrium geometries. The correlation energies per bond are determined by a fit to the CCSD(T)/CBS benchmarks. It can neither improve the equilibrium structures nor discern conformers or positional isomers, yet its accuracy for reaction energies rivals that of the second-order Møller–Plesset perturbation theory, which is far more expensive. Its promising performance underscores the possibility that surprisingly compact, chemically intuitive molecular fragments exist into which correlation energies can be partitioned, leading to various ultrafast correlation-energy estimators tailored to different purposes.

Binding energy↗
DOE OSTI2021

Elucidating the Location of Cd 2+ in Post-synthetically Treated InP Quantum Dots Using Dynamic Nuclear Polarization 31 P and 113 Cd Solid-State NMR Spectroscopy

Indium phosphide quantum dots (InP QD) are a promising alternative to traditional QD materials that contain toxic heavy elements such as lead and cadmium. However, InP QD obtained from colloidal synthesis are often plagued by poor photoluminescence quantum yields (PL-QYs). In order to improve the PL-QY of InP QD, a number of post-synthetic treatments have been devised. Recently, it has been shown that InP post-synthetically treated with Lewis acid metal divalent cations (M-InP) exhibit enhanced PL-QY; however, the molecular structure and mechanism behind the improved PL-QY are not fully understood. Here, to determine the surface structure of M-InP QD, dynamic nuclear polarization surface-enhanced nuclear magnetic resonance spectroscopy (DNP SENS) experiments were employed on a series of InP magic size clusters treated with Cd ions, InP QD, cadmium phosphide (Cd 3 P 2 ) QD, and Cd-treated InP QD (Cd–InP QD). With the use of DNP SENS, we were able to obtain the 1D 31 P and 113 Cd NMR spectra, 113 Cd{ 31 P} rotational-echo double-resonance (REDOR) NMR spectra, and 31 P{ 113 Cd} dipolar heteronuclear multiple quantum correlation (D-HMQC) sequence. Changes in the phosphide 31 P chemical shifts after Cd treatment provide indirect evidence that some Cd alloys into the sub-surface regions of the particle. DNP-enhanced 113 Cd solid-state NMR spectra suggest that most Cd ions are coordinated by oxygen atoms from either carboxylate ligands or surface phosphate groups. 113 Cd{ 31 P} REDOR and 31 P{ 113 Cd} D-HMQC experiments confirm that a subset of Cd ions are located on the surface of Cd–InP QD and coordinated with phosphate groups.

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

Effect of Composition and Local Environment on CO 2 Adsorption on Nickel and Magnesium Oxide Solid Solutions

CO 2 adsorption energies on the (100) surfaces of a nickel oxide doped with Mg, magnesium oxide doped with Ni, and their 50:50 solid solution were calculated using density functional theory. The composition and atomic arrangement of the adsorption site was varied to understand how the local environment affects CO 2 adsorption and the basicity of the surfaces at the atomic level. The dispersive and electronic contributions to the adsorption energies were quantified, and the results indicate that the variation of the adsorption energy with adsorption site configuration and metal composition is dominated by electronic interactions. Interestingly, for magnesium oxide doped with nickel, a single substitution can create stronger CO 2 binding sites, which implies stronger basic sites, even though nickel oxide is less basic than magnesium oxide. The effect of double substitution at the binding site can be reasonably approximated by summing the effects of single substitutions. Furthermore, this work provides guidance for the preparation of metal oxides with tailored Lewis basicity.

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

Influence of Domain Size and Support Composition on the Reducibility of SiO 2 and TiO 2 Supported Tungsten Oxide Clusters

Supported tungsten oxides are widely used in a variety of catalytic reactions. Depending on the support, the cluster size, oxidation state, reducibility and speciation of the tungsten oxides can widely differ. When promoted with a platinum group metal, the resulting spillover of hydrogen may facilitate the reduction of supported tungsten oxide species, depending on the support. High resolution scanning transmission electron microscopy imaging showed nanometer scale WO x clusters were synthesized on SiO 2 whereas highly dispersed species were formed on TiO 2 . Results from H 2 -temperature-programmed reduction showed the presence of Pd lowered the initial reduction temperature of SiO 2 -supported WO x species but interestingly did not affect that of TiO 2 -supported WO x . X-ray photoelectron and absorption spectroscopies showed the W atoms in SiO 2 -supported WO x species reduce from a +6 oxidation state to primarily +5 after thermal treatment in 5% H 2 , while the fraction of W in the +5 oxidation state was relatively unaffected by reduction treatment of TiO 2 -supported WO x . The unusual behavior of TiO 2 -supported WO x was explained by quantum chemical calculations that reveal the lack of change in the oxidation state of W is attributed to charge delocalization on the surface atoms of the titania support, which does not occur on silica. Moreover, modeling results at <600 K in the presence of H 2 suggest the formation of Brønsted acid sites, and the absence of Lewis acid sites, on larger aggregates of WO x on silica and all cluster sizes on titania. These results provide experimental and theoretical insights into the nature of supported tungsten oxide clusters under conditions relevant to various catalytic reactions.

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

First-Principles Study of Molecular Hydrogen Activation by Defects in Boron Nitride

Here, we used density functional theory simulations in combination with ab initio thermodynamics to determine the H 2 partial pressure (p H2 )-dependent energetics associated with H 2 activation and recovery at various defect sites in hexagonal boron nitride (h-BN). We found that some defects are very reactive with hydrogen, thereby definitely trapping hydrogen in defective h-BN. However, depending on hydrogen partial pressure, less reactive defect sites can be populated. Because of the lower binding capability of these sites, they would allow hydrogen to be recycled and recovered. For small defect sizes, we found that hydrogen preferentially binds to nitrogen sites by forming N–H bonds, and if no N sites are available then boron sites would be the next to bind hydrogen. Hydrogen dissociation via frustrated Lewis pair is found to be more favorable than forming only N–H bonds but only if the defect size is large enough to accommodate steric effects. For specific conditions such as T = 400 K, p H2 = 1 bar, and only considering one molecular H 2 per defect, three defects, namely, the N monovacancy, 3V(1B2N), and hexagonal 6V(3B3N) could play a role in both the activation and recycling of H 2 as they would be reacting enough to allow a favorable splitting of H 2 while not binding too strongly to allow its recovery. More broadly, a range of p H2 and hydrogen loading conditions were investigated for different types of defects and the finding suggests that p H2 could be used to fine-tune the Gibbs free energy of hydrogenation, thereby allowing several types of defects at different hydrogen loading contents to play a role in the activation/recovery process of H 2 in defective h-BN.

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

Energy Barriers for H 2 Uptake and Release by Defects in Boron Nitride

Density functional theory simulations (DFT) have been used in combination with the climbing image nudged elastic band method (CI-NEB) to determine the energy barriers required to dissociate H 2 at four types of h-BN defects and evaluate the potential for reacted H species to hop to adjacent available sites. The defects were selected based on previous work in which ab initio thermodynamics was used to identify specific defects with optimal thermodynamics for reversible H 2 storage, that is, the defects would dissociate molecular H 2 while not binding H species too strongly so that hydrogen release is favorable. The four defects investigated are the N and B monovacancies, which only offer either B or N defective sites respectively, as well as larger cluster vacancy defects named 3V(1B2N) and hexagonal 6V(3B3N), which present a mixture of B and N defect sites available for H binding. While homogeneous H 2 dissociation by B and N monovacancies have energy barriers larger than 0.4 eV, we found that mixed BN terminated defects have energy barrier lower than 0.4 eV for H 2 dissociation. In particular, H 2 dissociation by the hexagonal 6V(3B3N) defect, exclusively made of Frustrated Lewis Pairs (FLPs), is almost barrierless. The energy barrier for subsequent H hopping to available adjacent B or N sites of the defect were also calculated. It was found that the hopping of H species generally involves high energy barriers ranging from 0.26 eV to 2.57 eV. In conclusion, this work completes previous thermodynamic theoretical investigations and provides a more comprehensive picture of H 2 reaction with defective h-BN for potential H 2 storage and recovery.

Sassi, Michel J. [Pacific Northwest National Labor↗
DOE OSTI2024

M IV /Co –I (M = Zr, Hf) Bis(phosphinoamide) Complexes with η 6 - and η 4 -Arenes

Despite their relevance to catalysis, low-/subvalent cobalt complexes are difficult to synthesize and isolate. Consequently, very few “cobaltate” complexes are known and there is a lack of architectural diversity in this field. Lewis acidic d 0 group IV metals have been demonstrated to stabilize Co –I centers via metal–metal bonds. Herein, we report the synthesis of bis(phosphinoamide) heterobimetallic M IV /Co –I arene complexes (M = Zr, Hf). The driving force to maintain the aromaticity of the arenes dictates the hapticity of the Co-bound arene ligands and influences the binding arrangement of the phosphinoamide ligands. Benzene and toluene were observed to bind η 6 to the Co –I center, forcing dissociation of one of the phosphinoamide ligands, whereas η 4 -coordination of anthracene allows both phosphinoamide ligands to remain bound to the Co center. The identity of both the arene and the group IV metal ion starkly influence the lability of the arene. For instance, the Co-bound benzene ligand in the Zr IV /Co –I benzene complex rapidly exchanges with C 6 D 6 in solution, whereas toluene/C 6 D 6 exchange is much slower and appreciable C 6 H 6 /C 6 D 6 exchange is not observed for the Hf analogue. The Zr IV /Co –I benzene complex loses benzene upon repeated exposure to vacuum to form an arene-free tetrametallic dimer.

aromatic compounds↗
DOE OSTI2022

An Efficient Copper-Based Redox Shuttle Bearing a Hexadentate Polypyridyl Ligand for DSCs under Low-Light Conditions

A Cu complex featuring a hexadentate ligand was synthesized and evaluated as a redox shuttle in dye-sensitized solar cell (DSC) devices, which exhibited excellent performance under low-light conditions. Cu-based redox shuttles (RSs) have been shown to perform remarkably well under low-light conditions; however, most of the known Cu-based RSs employ bidentate pyridyl ligands and often require bulky flanking groups adjacent to the nitrogen donors of these ligands to prevent distortion and binding of exogenous Lewis bases such as 4- tert -butylpyridine (TBP) that are added to enhance cell performance. Without the bulky substituents, the bidentate ligands are susceptible to ligand exchange with TBP. In this context, we have developed a Cu-based RS with a preorganized multidentate ligand designed to facilitate efficient electron transfer kinetics and high stability via the chelate effect. The Cu system, [Cu(bpyPY4)] 2+/+ , reported here is supported by the hexadentate polypyridyl ligand bpyPY4 (6,6'-bis(1,1-di(pyridine-2-yl)ethyl)-2,2'-bipyridine) and examined as a RS in DSCs. From X-ray crystallography and variable-temperature 1 H NMR studies, bpyPY4 provides a dynamic coordination environment around the metal center. Cyclic voltammetry and UV–visible and NMR spectroscopy indicate that noncoordinated pyridyl donors block binding of TBP to copper. DSC devices using [Cu(bpyPY4)] 2+/+ as the redox electrolyte gave a power conversion efficiency (PCE) value of 4.9% under 1 sun illumination (100 mW/cm 2 ). Strikingly, the device performance increased to 11.11% when irradiated with 2400 lux (0.5 mW/cm 2 ) via a fluorescent lamp light source and improved further to 15.2% PCE at 13500 lux (2.10 mW/cm 2 ). In conclusion, the Cu redox shuttle is an intriguing candidate for implementation with narrow band gap sensitizers with low oxidation potentials, which are important for high photocurrent DSC devices.

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

Ambient Pressure XPS Investigation of Thermally Stable Halide Perovskite Solar Cells via Post-Treatment

Long-term thermal stability is one limiting factor that impedes the commercialization of perovskite solar cell. Inspired by our prior results from machine learning, we discover that coating a thin layer of 4,4’-dibromotriphenylamine (DBTPA) on top of a CH 3 NH 3 PbI 3 (MAPbI 3 ) thin film can improve the stability of the resultant perovskite solar cells. The passivated perovskite solar cells retained more than 96% of their initial power conversion efficiency over 1000 h at 85 °C in N2 atmosphere without encapsulation. Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) was employed to investigate the evolution of composition and evaluate thermal and moisture stability by in-situ studies. A comparison between pristine MAPbI 3 films and DBTPA-treated films shows the DBTPA treatment suppresses the escape of iodide and methylamine up to 150 °C under 5 mbar humidity. Furthermore, we have used ATR-FTIR and XPS to probe the interactions between DBTPA and MAPbI3 surface. The results prove that DBTPA coordinate with perovskite by Lewis acid-base and cation-π interaction. Compared with the 19.9% efficiency of pristine sample, the champion efficiency of passivated sample reaches 20.6%. Finally, our results reveal DBTPA as a new post-treating molecule that not only leads to the improvement of photovoltaic efficiency but also thermal and moisture stability.

14 SOLAR ENERGY↗
DOE OSTI2020

Dialing in Catalytic Sites on Metal Organic Framework Nodes: MIL-53(Al) and MIL-68(Al) Probed with Methanol Dehydration Catalysis

Many metal organic frameworks (MOFs) incorporate metal oxide clusters as nodes. Node sites where linkers are missing can be catalytic sites. We now show how to dial in the number and occupancy of such sites in MIL-53 and MIL-68, which incorporate aluminum-oxide-like nodes. Here, the methods involve modulators used in synthesis and postsynthesis reactions to control the modulator-derived groups on these sites. We illustrate the methods using formic acid as a modulator, giving formate ligands on the sites, and these can be removed to leave μ 2 -OH groups and open Lewis acid sites. Methanol dehydration was used as a catalytic reaction to probe these sites, with infrared spectra giving evidence of methoxide ligands as reaction intermediates. Control of node surface chemistry opens the door for placement of a variety of ligands on a wide range of metal oxide cluster nodes for dialing in reactivity and catalytic properties of a potentially immense class of structurally well-defined materials.

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

Significant Role of Oxygen Dopants in Photocatalytic PFCA Degradation over h-BN

The activation of the C(sp 3 )–F bond is extremely difficult due to its unreactive nature. The importance of this bond activation is recently highlighted because extensive distribution of perfluorocarboxylic acids (PFCAs) (C n F 2n+1 COOH) has emerged as a challenging environmental issue. Photocatalytic degradation of PFCAs over a few semiconducting light absorbers is known to remove these water and soil resilient contaminants but with limited efficiency. This work reports density functional theory calculations, through which we present a detailed mechanistic study of photocatalytic degradation of CF 3 COOH (the shortest member of the PFCA family) over hexagonal boron nitride (h-BN). Here, our results clearly demonstrate that the existence of point defects is necessary to activate the h-BN plane for photocatalytic dissociation of the C–F bond. Specifically, we show that vacancies create strong Lewis acid or base sites (B or N vacancy, respectively) that facilitate the activation of the C(sp 3 )–F bond considerably. Furthermore, this study presents vivid theoretical evidence for the significant role of oxygen dopants, which mitigate the strength of the active sites and promote PFCA degradation over h-BN. Our calculations suggest that while the very stable intermediates generated during the reaction, in the case of h-BN with B or N vacancies, practically poison the catalyst, oxygen dopants make the degradation much more plausible and controllable. This work thus provides both an explanation for recently observed photocatalytic activity of h-BN to decompose PFCAs and valuable insights for exploring defected two-dimensional materials for activating and removing the fluorine-containing contaminants from water and soil.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Investigating the Influence of Hexanuclear Clusters in Isostructural Metal–Organic Frameworks on Toxic Gas Adsorption

The efficient capture of toxic gases, such as ammonia (NH 3 ) and sulfur dioxide (SO 2 ), can protect the general population and mitigate widespread air pollution. Metal–organic frameworks (MOFs) comprise a tunable class of adsorbents with high surface areas that can meet this challenge by selectively capturing these gases at low concentrations. In this work, we explored how modifying the metal ions in the node of an isostructural MOF series from a transition metal to a lanthanide or actinide influences the electronic environment of the node-based active site. Next, we investigated the adsorption properties of each MOF toward the relatively basic NH 3 and relatively acidic SO 2 gases. Within the NU-907 family of MOFs, we found that Zr 6 -NU-907 exhibits the best uptake toward NH 3 at low pressures, while Th 6 -NU-907 demonstrates the best low-pressure performance for SO 2 adsorption. Here, tracking the infrared (IR) stretching frequency of the node-based μ 3 -OH groups provides insights into the electronegativity of the metal ion and suggests that the most electronegative metal ion (Zr) affords the node with the best NH 3 uptake at low pressures. In contrast, the Th 6 node contains additional coordinated water groups relative to the other M 6 nodes, which appears to yield the MOF with the greatest affinity for SO 2 uptake that occurs predominately through reversible physisorption interactions. Finally, in situ NH3 IR spectroscopic studies indicate that both NH 4 + and Lewis-bound NH 3 species form during adsorption. Combined, these results suggest that tuning the electronic properties and structure of the node-based active site in an MOF presents a viable strategy to change the affinity of an MOF toward toxic gases.

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

Tunable Solid Acid Catalyst Thin Films Prepared by Atomic Layer Deposition

Solid acid catalysts, including zeolites and amorphous silica-aluminas (ASAs), are industrially important materials widely used in the fuel and petrochemical industries. The versatility of zeolites is due to the Brønsted acidity of the bridging hydroxyl and shape selectivity that can be tailored during and after synthesis. This is in contrast to amorphous silica-alumina, where tailoring acidity is a major challenge as the Brønsted acid structure in ASA is still debated. In both cases, however, the pore size and acidity cannot be tuned independently, and this is particularly limiting in the application of biomass conversion, where zeolite pores are too small for the molecules of interest. Herein, we present a method using atomic layer deposition (ALD) to prepare thin films of solid acid materials where the ratio of Brønsted to Lewis acid sites can be tuned precisely. This capability, combined with the sub-nm pore size control afforded by ALD yields a powerful and flexible method for synthesizing solid acid catalysts inside virtually any mesoporous host. We demonstrate the utility of these materials in two acid-catalyzed reactions relevant to biomass conversion: (1) Meerwein–Ponndorf–Verley–Oppenauer (MPVO) reaction and dehydration of fructose and (2) cascade reaction of glucose to 5-hydroxymethylfurfural. Finally, we propose a plausible structure for the Brønsted acid sites in our materials based on infrared spectroscopy and solid-state nuclear magnetic resonance measurements and density functional theory calculations and argue that this same structure might apply to conventional ASAs as well.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Molecular Additive Engineering for Process-Humidity Robustness and Reproducible Fabrication of Perovskite Solar Cells and Modules

The commercialization of perovskite solar cells (PSCs) faces significant challenges due to their sensitivity to environmental humidity, which compromises film crystallization and device stability. Here, we introduce diphenylvinylphosphine (DPVP) as a Lewis base additive that enhances the performance and reproducibility of PSCs fabricated under ambient-air conditions. DPVP suppresses moisture-induced defect formation and stabilizes crystallization within realistic process-humidity ranges (20–40% relative humidity) commonly encountered in laboratory and pilot-scale manufacturing environments. It improves film uniformity, reduces trap densities, and yields highly reproducible device performance, enabling champion PCEs of 24.2% in small-area devices and 20.5% in blade-coated 12 cm 2 mini-modules. Furthermore, DPVP-assisted modules exhibit enhanced stability, retaining over 85% of their initial efficiency after 900 h of maximum power point tracking (MPPT) at 65 °C. This study demonstrates a humidity-resilient and scalable additive strategy for ambient-air perovskite photovoltaic manufacturing.

defect passivation↗
DOE OSTI2021

Identifying the Catalytic Active Site for Propylene Metathesis by Supported ReO x Catalysts

A series of supported ReO x catalysts were investigated that allowed identifying the unique surface anchoring sites on oxide supports responsible for activating the surface ReO 4 sites for propylene metathesis (the catalytic active site). The catalysts were synthesized by incipient-wetness impregnation of aqueous HReO 4 onto the oxide supports (Al 2 O 3 , ZrO 2 , TiO 2 , SiO 2 and CeO 2 ), characterized under dehydrated and propylene metathesis reaction conditions with in situ spectroscopy (Raman, DRIFTS, UV-Vis and NAP-XPS), and chemically probed (CH 3 CH=CH 2 -TPSR, CH 2 =CH 2 /CH 3 CH=CHCH 3 titration and steady-state self-metathesis of propylene to ethylene and 2-butene). The initially calcined supported rhenia species anchor as isolated surface Re 7+ O 4 sites on the oxide supports by reacting with the surface hydroxyls (terminal S-OH, bridged S-OH-S and tricoordinated S 3 -OH) of the oxide supports. The specific oxide support was found to control the number of activated sites (Al 2 O 3 >> ZrO 2 > CeO 2 > TiO 2 > SiO 2 ) and propylene metathesis activity (Al 2 O 3 >> ZrO 2 >> TiO 2 ~ CeO 2 ~ SiO 2 ) revealing that the oxide support action is a potent ligand for the surface ReO x sites. The activation and specific activity of the surface ReO x sites depend on several factors (nature of surface hydroxyls (S 3 -OH > S-OH-S > S-OH), coordination of the oxide support surface cation (ZrO 7 , AlO 6 , CeO 4 ) and electronegativity of the oxide support cation (SiO 2 > Al 2 O 3 > TiO 2 > ZrO 2 > CeO 2 ). No relationships exist between olefin metathesis activity and acid strength of surface Lewis and Brønsted sites. Here, prior studies primarily focused on supported ReO x /Al 2 O 3 and the lack of examination of non-Al 2 O 3 supported rhenia catalysts precluded comparison between efficient and inefficient olefin metathesis catalysts, which prevented identifying the catalytic active site for olefin metathesis by supported ReO x catalysts.

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

Modification of Catalytic Properties of Hollandite Manganese Oxide by Ag Intercalation for Oxidative Acetalization of Ethanol to Diethoxyethane

The effect of addition of Ag to the catalytic properties of hollandite manganese oxide (HMO) was investigated for the oxidative acetalization of ethanol to diethoxyethane. Based on analysis with HRTEM, XRD, and EXAFS, Ag introduced onto HMO by deposition/precipitation was found to be present in different forms in the final catalyst depending on the calcination temperature. It could exist as nanoparticles on the outside surface of HMO nanorods for samples calcined at 60 °C, and as Ag atoms intercalated into the tunnels of the HMO structure for samples calcined at 500 °C. NH 3 desorption results showed that intercalation of Ag resulted in stronger Lewis acidic sites on HMO, which DFT computational results suggested to be due to Ag-induced electron redistribution in the HMO framework. Here, the intercalation of Ag atoms also made the HMO more easily reducible by lowering the H 2 reduction temperature from 500 to 200 °C. Consequently, the sample with intercalated Ag was more active for ethanol oxidation to acetaldehyde, achieving nearly 100% conversion of ethanol and acetaldehyde by 360 °C, and acetalization of acetaldehyde with ethanol to produce diethoxyethane selectively, resulting in 93.5% diethoxyethane yield, which was 10% higher than with samples containing Ag nanoparticles on HMO. This study demonstrated a little-studied phenomenon in which a metal alters the catalytic properties of an oxide electronically but not structurally and without direct participation in the reaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗