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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Dimerization of Linear Butenes on Zeolite-Supported Ni 2+

Nickel- and alkali-earth-modified LTA based zeolites catalyze the dimerization of 1-butene in the absence of Bronsted acid sites. The catalyst reaches over 95% selectivity to n-octenes and methylheptenes. The ratio of these two dimers is markedly influenced by the parallel isomerization of 1-butene to 2-butene, shifting the methylheptene/octene ratio from 0.7 to 1.4 as the conversion increases to 35%. At this conversion, the thermodynamic equilibrium of 90% cis- and trans-2-butenes is reached. Conversion of 2-butene results in methylheptene and dimethylhexene with rates that are 1 order of magnitude lower than those with 1-butene. The catalyst is deactivated rapidly by strongly adsorbed products in the presence of 2-butene. The presence of pi-allyl-bound butene and Ni-alkyl intermediates was observed by IR spectroscopy, suggesting both to be reaction intermediates in isomerization and dimerization. Product distribution and apparent activation barriers suggest 1-butene dimerization to occur via a 1'-adsorption of the first butene molecule and a subsequent 1'- or 2'-insertion of the second butene to form octene and methylheptene, respectively. The reaction order of 2 for 1-butene and its high surface coverage suggest that the rate-determining step involves two wealdy adsorbed butene molecules in addition to the more strongly held butene.

Ehrmaier, Andreas↗
DOE OSTI2018

Operando Structure Determination of Cu and Zn on Supported MgO/SiO 2 Catalysts during Ethanol Conversion to 1,3-Butadiene

Electronic structure and reactivity of Cu- and Zn-promoted wet kneaded MgO/SiO 2 catalysts was interrogated during ethanol reaction to 1,3-BD. A multimodal nature of characterization, including in situ or operando X-ray, electron, light spectroscopies and steady state reactivity measurements demonstrated critical new information on the temporal evolution of the catalyst active sites including key measurements performed operando using synchrotron source (EXAFS and XANES). In situ DRIFT spectroscopy allowed to decouple the aldol condensation and dehydrogenation reactive steps due to the promotion with enhanced ability to carry out aldol condensation, as correlated with the steady state reactivity experiments . In situ UV-Vis spectroscopy presented a complex picture of the adsorbates with π- π* electronic transitions due to the allylic cations, cyclic or aromatic species while also suggesting oligomeric CuO species were formed. Operando X-ray measurements combined with ab initio multiple scattering modelling performed as a function of temperature identified a new transient intermediate assigned to a 4-fold coordinate Cu species that was key leading to increase in Cu-Cu pair number. For the first time, two types of Zn pairs, namely Zn-O and Zn-Mg, were identified during X-ray analysis under operating conditions. With Zn nearly 6-coordinated when in the vicinity of Mg while Zn-O species coordinated to nearly 4 nearest neighbors. The data suggest that such supported catalyst deactivation might proceed not only via carbon coking mechanism but also through the dispersed Cu site diffusion and growth due to the nearest neighbor oxygen atoms loss. The results presented suggest intermediates for segregation/deactivation mechanisms for a broader set of supported Cu and Zn catalysts used for alcohol upgrading catalytic reactions.

1,3-butadiene↗
DOE OSTI2019

Catalysis by Metal Organic Frameworks: Perspective and Suggestions for Future Research

Metal organic frameworks (MOFs) have drawn wide attention as potential catalysts, offering high densities of catalytic sites in high-area porous solids, some with stabilities at high temperatures. The field is at an early stage, characterized by numerous discoveries and novel demonstrations of catalytic properties associated with the crystalline structures of MOFs, but applications of MOFs as catalysts are still lacking. In this perspective we summarize advantages and limitations of MOFs as catalysts and fundamental issues to be addressed about their potential applications. MOF framework compositions and pore structures can strongly influence catalytic performance, allowing, for example, shape-selective and bifunctional catalysis, but research is needed to quantify reaction/transport processes in MOFs, identify catalytic sites, and determine intrinsic catalytic reaction rates. Progress is hindered by the lack of understanding of the heterogeneity of MOFs, with catalytic sites sometimes being in structures such as defects not determined by X-ray diffraction crystallography. Determination of the dynamics of MOFs and their catalytic sites, as well as the intrinsic kinetics of catalytic reactions, will help to advance guidelines for synthesizing optimum catalysts. Further, MOFs present challenges related to stability and regeneration as catalysts, some associated with the unique nature of MOFs, such as the node–linker bonds, which can break during catalysis. There are opportunities to understand these matters in depth and to find conditions of catalytic operation that minimize the processes leading to deactivation.

catalysis (heterogeneous), materials and chemistry↗
DOE OSTI2019

Selective Production of Aromatics by Catalytic Fast Pyrolysis of Furan with In Situ Dehydrogenation of Propane

Catalytic fast pyrolysis (CFP) of furan was studied with the co-feeding of propane over ZSM-5, CrOx/Al2O3, and mixed catalysts with both ZSM-5 and CrOx/Al2O3 to combine the dehydrogenation of propane and CFP of furan in the presence of in situ generated propylene. With 15 vol % propane co-feeding, a slight increase in aromatic yield was observed over ZSM-5 catalyst. These enhancement was further improved by using mixed catalysts consisting of CrOx/Al2O3 and ZSM-5 with different weight ratios. Over the best mixed catalyst with CrOx/Al2O3 to ZSM-5 weight ratio of 2, a nearly 2-fold increase in the aromatic yield was obtained. The toluene selectivity was also increased from 37% to 50%. The increase in aromatic yield is directly dependent on the propane to total flow volume ratio. Moreover, the coke formation within ZSM-5 was also reduced, leading to a slower catalyst deactivation. From mechanistic studies, a two-step cascade reaction pathway was observed over the bifunctional mixed catalysts. It was proposed that propane dehydrogenates to propylene over CrOx/Al2O3. The propylene then reacts with furan within ZSM-5 catalyst to selectively form aromatics. This work demonstrates a simple and economical strategy to further improve the CFP technique.

bio-inspired↗
DOE OSTI2019

Analogy between Enzyme and Nanoparticle Catalysis: A Single-Molecule Perspective

Catalysis as a field is classically divided into three areas: homogeneous, heterogeneous, and biological catalysis.1 For the latter two, i.e., biological catalysis and heterogeneous catalysis, their dissimilarity can be apparent intuitively, from the scenes of fruit fermentation in a rural winery to make wine and oil refining in a process plant to produce gasoline. In addition to the practical differences, technological terms common in both areas show divergences in meaning. Here, a highly relevant example is the term turnover number.2 It refers to the maximum number of substrate molecules converted to products per enzyme molecule per second, often written as k cat in enzyme catalysis; while the same term means the number of moles of reactants that a mole of catalyst converts before deactivation, usually abbreviated as TON in heterogeneous catalysis.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Catalysts in Coronas: A Surface Spatial Confinement Strategy for High-Performance Catalysts in Methane Dry Reforming

One of the grand challenges in industrial catalytic processes is the inevitable sintering and aggregation of conventional supported catalysts to large particles, leading to the decrease of activity and even deactivation with time. Herein, a surface spatial confinement strategy was employed to design high-performing catalysts for the dry reforming of methane (DRM). Specifically, active nickel (Ni) nanoparticles (NPs) were confined on the surface of a dendritic mesoporous silica (DMS) in the form of the “catalysts in coronas”. The Ni/DMS catalyst exhibited a high catalytic performance close to its equilibrium conversion (76% conversion for CH4 at 700 °C). More importantly, the prepared catalyst remained stable after 145 h time-on-stream at 700 °C without noticeable carbon deposition. This sintering and coking resistance was found to arise from the surface spatial confinement effect in which the three-dimensional dendritic layers in the corona posted a steric barrier against migration and aggregation of Ni NPs and size of Ni NPs was controlled below 5 nm, hence against sintering and coking. Meanwhile, the mesoporous feature of the layered wall facilitated mass transport of reactants to Ni species and further boosted catalysis. This strategy should be broadly applicable to a range of metal- and metal oxide-supported catalysts in high-temperature heterogeneous reactions, such as DRM, water gas shift reaction, and vehicle emission control related reactions.

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

Enhanced Activity of Heterogeneous Pd(II) Catalysts on Acid-Functionalized Metal–Organic Frameworks

Single-site heterogeneous catalysts (SSHCs) play important roles in fundamental science and technology, owing to the molecular level control of structure–support interactions that is possible in these systems. Recently, SSHCs supported by acidic oxides have attracted particular interest because catalytically active metal centers can be formed at the surface sites. Here, we incorporated a palladium SSHC in phosphated and sulfated metal–organic frameworks (MOFs), hafnium-based MOF-808 (Hf-MOF-808-PO 4 and Hf-MOF-808-SO 4 ). The structural and electronic properties of the Pd(II) sites coordinated to the acidic sites in these MOFs were investigated through X-ray photoelectron spectroscopy, vibrational spectroscopy, X-ray crystallographic techniques, catalytic studies, and quantum mechanical electronic structure calculations employing density functional theory. We demonstrated that the presence of node-bound acidic functional groups stabilizes the Pd(II) site in these MOFs, resulting in enhanced catalytic activities (compared to in the nonacid functionalized Hf-MOF-808) in the oxidative Heck reaction where Pd(II) is the active species. The density functional calculations support the interpretation that the acid functionalization of the MOF node can stabilize the Pd(0) intermediate state during the catalytic reactions, thereby suppressing Pd(0) aggregation leading to catalyst deactivation. Furthermore, these findings offer insights and methodology for the catalytic investigation of SSHCs in MOFs.

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

Kinetic Monte Carlo Simulations Unveil Synergic Effects at Work on Bifunctional Catalysts

The interaction among metal particles and the support in heterogeneous catalysis has been the subject of a large number of studies. Although strong metal–support interactions can lead to deleterious catalyst deactivation and the underlying mechanism is well understood, in other cases the effect may beneficially enhance the catalytic activity and/or selectivity with no clear picture of the chemistry involved. Strong metal–support interactions make Au nanoparticles dispersed on MoC a highly active catalyst for the low-temperature water-gas shift reaction (WGSR). In this work, by using kinetic Monte Carlo (kMC) simulations, we unravel the origin of the experimentally observed high WGSR activity of Au/MoC. The kMC simulations provide strong evidence for a cooperative effect between the different regions of the catalyst: the clean MoC regions are responsible for adsorbing and dissociating water molecules, and the vicinity of the Au adclusters contributes to COOH formation. The information thus obtained goes beyond that obtained solely from free-energy landscapes and constitutes a step forward toward the rational design of catalysts. Importantly, the simulations and analysis described here are general and can be applied to other complex systems involving different catalytic regions and a large number of surface processes.

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

Role of Boron in Enhancing the Catalytic Performance of Supported Platinum Catalysts for the Nonoxidative Dehydrogenation of n -Butane

Platinum-based supported catalysts for hydrocarbon conversion are among the most effective for selective dehydrogenation and isomerization processes. However, high process temperatures and the possibility of coke formation require catalyst modifications to mitigate such effects. One of the emerging approaches to prevent platinum catalyst deactivation is the use of boron additives that have been proposed to prevent coking. Despite such a valuable property of boron, the mechanisms for extending the catalyst lifetime and the decrease in coke formation based on this method are still poorly understood. The type and transformations of boron species on silica surface were investigated as a function of boron introduction, platinum addition, catalyst activation, and catalytic reactivity by a combination of X-ray photoelectron spectroscopy, electron microscopy, solid-state nuclear magnetic resonance spectroscopy, and density functional theory calculations to uncover the possible role of boron modification in improving the catalytic performance. Catalytic nonoxidative dehydrogenation of n-butane revealed that incorporation of boron improved the catalytic activity (similar to 3x) and stability of Pt/SiO 2 . The role of boron in enhancing catalytic performance was attributed to facilitating the migration of alkyl groups from platinum catalytic centers to tetrahedrally coordinated boron sites.

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

CO 2 Conversion to Butene via a Tandem Photovoltaic–Electrochemical/Photothermocatalytic Process: A Co-design Approach to Coupled Microenvironments

Here, we developed a tandem, unassisted, solar-driven electrochemical and photothermocatalytic process for the single-pass conversion of CO 2 to butene using only simulated solar irradiation as the energetic input. The two-step process involves electrochemical CO 2 reduction (CO 2 R) to ethylene followed by ethylene dimerization to butene. We assessed two unassisted electrochemical setups to concentrate ethylene in the CO 2 R reactor, achieving concentrations up to 5.4 vol.% with 1.8% average solar-to-ethylene conversion and 5.6% average CO 2 -to-ethylene single-pass conversion under 1-sun illumination. When passed through the photothermocatalytic ethylene oligomerization reactor, we generated 600 ppm of butene under 3-sun illumination. Through analysis of this process, we identified that the presence of H 2 , CO, and H 2 O leads to rapid deactivation of the Ni-based ethylene oligomerization catalyst.

14 SOLAR ENERGY↗
DOE OSTI2026

Depolymerization of Vinyl Polymers

Depolymerization is a promising approach to reduce plastic waste by regenerating monomers from polymers, presenting a compelling solution to maintain a circular polymer economy. However, vinyl polymers with all-carbon backbones are especially difficult to depolymerize due to significant thermodynamic and kinetic barriers. Developments in reversible-deactivation radical polymerization and catalytic methods demonstrate how tuning polymer structure and reaction conditions can address these challenges. This Viewpoint revisits early studies on radical depolymerization and recent advances enabling monomer recovery at lower temperatures. Exciting current trends to utilize depolymerization as a strategy for tuning polymer material properties and upcycling waste polymer to high-value products are discussed. Finally, we outline key directions to make vinyl polymer depolymerization scalable, efficient, and economically viable.

depolymerization↗
DOE OSTI2024

Sintering Mechanism of Pt/Al 2 O 3 in Complex Emission Gases Elucidated via In Situ Environmental STEM

Emission control catalysts are crucial for protecting human health by preventing the release of harmful gases and unburnt fuel into the atmosphere. These catalysts often face deactivation through sintering processes in high-temperature, chemically reactive environments containing multiple gas species. Here, we use in situ environmental scanning transmission electron microscopy to monitor the sintering behavior and transient morphologies of Pt/Al 2 O 3 in various relevant gas environments through controlled experiments. Our results reveal the particle migration and atomic ripening behavior of Pt/Al 2 O 3 at the atomic scale in the presence of water vapor and oxygen, which differs from behaviors observed in single gas environments. We identify an atomic ripening mechanism involving the dissociation and migration of Pt adatom chains from Pt nanoparticles, observed only in combinational gases. Finally, these findings provide valuable insights into catalyst degradation behavior in complex gas environments.

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

Toward Spatial Control of Reaction Selectivity on Photocatalysts Using Area-Selective Atomic Layer Deposition on the Model Dual Site Electrocatalyst Platform

Photocatalytic water splitting is a promising route to low-cost, green H 2 . However, this approach is currently limited in its solar-to-hydrogen conversion efficiency. One major source of efficiency loss is attributed to the high rates of undesired side and back reactions, which are exacerbated by the proximity of neighboring oxidation and reduction sites. Nanoscopic oxide coatings have previously been used to selectively block undesired reactants from reaching active sites; however, a coating encapsulating the entire photocatalyst particle limits activity as it cannot facilitate both half-reactions. In this work, area selective atomic layer deposition (AS-ALD) was used to selectively deposit semipermeable TiO 2 films onto model metallic cocatalysts for enhancing reaction selectivity while maintaining a high overall activity. Pt and Au were used as exemplary reduction and oxidation cocatalyst sites, respectively, where Au was deactivated toward ALD growth through self-assembled thiol monolayers while TiO 2 was coated onto Pt sites. Electroanalytical measurements of monometallic thin film electrodes showed that the TiO 2 -encapsulated Pt effectively suppressed undesired H 2 oxidation and Fe(II)/Fe(III) redox reactions while still permitting the desired hydrogen evolution reaction (HER). A planar model photocatalyst platform containing patterned interdigitated arrays of Au and Pt microelectrodes was further assessed using scanning electrochemical microscopy (SECM), demonstrating the successful use of AS-ALD to enable local reaction selectivity in a dual-reaction-site (photo)electrocatalytic system. Finally, interdigitated microelectrodes having independent potential control were used to show that selectively deposited TiO 2 coatings can suppress the rate of back reactions on neighboring active sites by an order of magnitude compared with uncoated control samples.

08 HYDROGEN↗
DOE OSTI2015

Chemical and phase evolution of amorphous molybdenum sulfide catalysts for electrochemical hydrogen production [Chemical and phase evolution of amorphous molybdenum sulfide catalysts for electrochemical hydrogen production directly observed using environmental transmission electron microscopy]

Amorphous MoS x is a highly active, earth-abundant catalyst for the electrochemical hydrogen evolution reaction. Previous studies have revealed that this material initially has a composition of MoS 3 , but after electrochemical activation, the surface is reduced to form an active phase resembling MoS 2 in composition and chemical state. However, structural changes in the Mo Sx catalyst and the mechanism of the activation process remain poorly understood. In this study, we employ transmission electron microscopy (TEM) to image amorphous MoS x catalysts activated under two hydrogen-rich conditions: ex situ in an electrochemical cell and in situ in an environmental TEM. For the first time, we directly observe the formation of crystalline domains in the MoS x catalyst after both activation procedures as well as spatially localized changes in the chemical state detected via electron energy loss spectroscopy. Using density functional theory calculations, we investigate the mechanisms for this phase transformation and find that the presence of hydrogen is critical for enabling the restructuring process. Our results suggest that the surface of the amorphous MoS x catalyst is dynamic: while the initial catalyst activation forms the primary active surface of amorphous MoS 2 , continued transformation to the crystalline phase during electrochemical operation could contribute to catalyst deactivation. Finally, these results have important implications for the application of this highly active electrocatalyst for sustainable H 2 generation.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Effect of Storage Conditions on Efficacy of Poly(ethylenimine)-Alumina CO 2 Sorbents

Solid amine sorbents are one of the primary components of DAC technologies that allow for the removal of ultradilute CO 2 from the atmosphere. A main drawback in the implementation of solid amine sorbents in industrial-scale DAC applications is their instability under certain operational or storage conditions over an extended period. In this work, the effect of storage temperature and gas composition in the storage headspace on the long-term stability of a poly(ethylenimine)-alumina (PEI/γ-Al 2 O 3 ) sorbent is explored. PEI/γ-Al 2 O 3 sorbents with 70 and 100% pore filling are aged under varying gases (N 2 , O 2 , Ar, 0.04% CO 2 −N 2 , CO 2 , and ambient air) in an oven (40 °C), at common ambient indoor temperature conditions (23 °C), or in a freezer (−4 °C). The CO 2 sorption capacity, as measured by thermogravimetric analysis (TGA), along with FTIR spectra of the fresh and aged sorbents, reveal that at 23 and −4 °C, storage under ambient air or inert gas (Ar) provides reasonable long-term stability, with <13% degradation over 12 and 5 months of storage. Interestingly, with storage at 40 °C, similar levels of deactivation were observed under pure O 2 and N 2 after 4 months of storage, which suggests that nonoxidative thermal reactions can occur under prolonged storage conditions under N 2 . In contrast, with storage under CO 2 , sorbent degradation is substantially suppressed compared to storage under N 2 , ambient air, O 2 , or Ar, yielding sorbents with no observable loss in capacity after 2 months, compared to a 66, 63, and 62% loss under N 2 , ambient air, and N 2 in the same period at 40 °C, respectively. Overall, these findings provide guidance for practical amine sorbent storage in academic or industrial settings where amine sorbents are used for carbon capture.

Atmospheric chemistry↗
DOE OSTI2020

Selective and Efficient Production of Biomass-Derived Vinylfurans

We describe a two-step catalytic process for the selective and rapid conversion of biomass-derived acetylfurans into vinylfurans. This is accomplished by nearly quantitatively reducing acetylfurans into furyl alcohols using a copper chromite catalyst and exploiting the promoter-like properties of ethanol, the solvent. Subsequently, furyl alcohol is dehydrated using solid-acid catalysts. Catalyst deactivation due to oligomeric species is a major issue, but the activity can be partially recovered by calcination. Optimization of reaction conditions showed that the selectivity could be increased by using nitrobenzene, a polar aprotic solvent. Here, the high-boiling point solvent allows the formation of vinylfurans with a selectivity of up to 85%; the product can be isolated in high purity by distillation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗