Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “ALKANE”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Regioselective Generation of Single‐Site Iridium Atoms and Their Evolution into Stabilized Subnanometric Iridium Clusters in MWW Zeolite

Abstract Preparation of supported metal catalysts with uniform particle size and coordination environment is a challenging and important topic in materials chemistry and catalysis. In this work, we report the regioselective generation of single‐site Ir atoms and their evolution into stabilized subnanometric Ir clusters in MWW zeolite, which are located at the 10MR window connecting the two neighboring 12MR supercages. The size of the subnanometric Ir clusters can be controlled by the post‐synthesis treatments and maintain below 1 nm even after being reduced at 650 °C, which cannot be readily achieved with samples prepared by conventional impregnation methods. The high structure sensitivity, size‐dependence, of catalytic performance in the alkane hydrogenolysis reaction of Ir clusters in the subnanometric regime is evidenced.

Liu, Lichen↗
DOE OSTI2022

High‐Field NMR, Reactivity, and DFT Modeling Reveal the γ‐Al 2 O 3 Surface Hydroxyl Network**

Abstract Aluminas are strategic materials used in many major industrial processes, either as catalyst supports or as catalysts in their own right. The transition alumina γ‐Al 2 O 3 is a privileged support, whose reactivity can be tuned by thermal activation. This study provides a qualitative and quantitative assessment of the hydroxyl groups present on the surface of γ‐Al 2 O 3 at three different dehydroxylation temperatures. The principal [AlOH] configurations are identified and described in unprecedented detail at the molecular level. The structures were established by combining information from high‐field 1 H and 27 Al solid‐state NMR, IR spectroscopy and DFT calculations, as well as selective reactivity studies. Finally, the relationship between the hydroxyl structures and the molecular‐level structures of the active sites in catalytic alkane metathesis is discussed.

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

Anomalous Role of Carbon in Pd‐Catalyzed Selective Hydrogenation

Carbonaceous species, including subsurface carbidic carbon and surface carbon, play crucial roles in heterogeneous catalysis. Many reports suggested the importance of subsurface carbon in the selective hydrogenation of alkynes over Pd‐based catalysts. However, the role of surface carbon has been largely overlooked. Here, we demonstrate that subsurface carbon in Pd is not responsible for the selectivity in acetylene hydrogenation. In contrast, the structure of surface carbonaceous species plays a decisive role in hydrogenation selectivity. Electron microscopy and spectroscopy evidence, along with theoretical modelling, reveal that partial graphitization of surface carbonaceous species results in unique spatial confinement of surface reaction intermediates, thus altering the reaction energy landscape in favour of ethylene desorption as opposed to over‐hydrogenation. This mechanism for selectivity control is analogous to enzyme catalysis, where the active centers selectively attract reactants and release products. Similar mechanism may be present in CO/CO 2 hydrogenation and alkane dehydrogenation reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Search, engineering, and applications of new oxidative biocatalysts

Abstract Most industrial enzymes are hydrolases, such as glycosidases and esterases. However, oxidoreductases have an unexploited potential for substituting harsh (and scarcely selective) chemical processes. A group of basidiomycetes are the only organisms degrading the aromatic lignin polymer, enabling the subsequent use of plant polysaccharides. Therefore, these fungi and their ligninolytic peroxidases are the biocatalysts of choice for industrial delignification and oxidative biotransformations of aromatic and other organic compounds. The latter also include oxygenation reactions, which are catalyzed with high regio/stereo selectivity by fungal peroxygenases. In search for novel and more robust peroxidases/peroxygenases, basidiomycetes from unexplored habitats were screened, and hundreds of genes identified in basidiomycete genomes (in collaboration with the DOE JGI). The most interesting genes were heterologously expressed, and the corresponding enzymes structurally‐functionally characterized. The information obtained enabled us to improve the enzyme operational and catalytic properties by directed mutagenesis. However, the structural‐functional relationships explaining some desirable properties are not established yet and, therefore, their introduction was addressed by ‘non‐rational’ directed evolution. Then, over 100 oxidative biotransformations were analyzed. Among them, it is noteworthy to mention the regio/stereo selective hydroxylation of long/short‐chain alkanes (a chemically challenging reaction), epoxidation of alkenes, and production of hydroxy‐fatty acids. Concerning aromatic oxygenations, the regioselective hydroxylation of flavonoids, and stereoselective hydroxylation/epoxidation of alkyl/alkenyl‐benzenes were among the most remarkable reactions, together with enzymatic hydroxylation of benzene (as an alternative for harsh chemical process). Finally, peroxidases and peroxygenases also showed a potential as delignification biocatalysts and in the decolorization of contaminant dyes from textile industries. © 2014 The Authors. Biofuels, Bioproducts and Biorefi ning published by Society of Chemical Industry and John Wiley & Sons, Ltd.

Martínez, Angel T.↗
DOE OSTI2018

Ultra-Stable and High-Cobalt-Loaded Cobalt@Ordered Mesoporous Carbon Catalysts: All-in-One Deoxygenation of Ketone into Alkylbenzene

Catalytic deoxygenation represents a straightforward and core methodology for fine-chemical production and biomass upgrading. Generally, the application of homogeneous metal complexes or heterogeneous noble-metal catalysts prevails in academia and the chemical industry. We introduce cobalt@ordered mesoporous carbon (Co@OMC) catalysts, which are constructed conveniently by a mechanochemical coordination self-assembly based on a renewable tannin precursor. Importantly, the Co@OMC catalysts with a high loading of in situ confined Co species promote the selective deoxygenation of various ketones, aldehydes, and alcohols efficiently into the corresponding alkanes under mild conditions. Therefore, a simple, inexpensive, and heterogeneous catalyst for selective deoxygenation can be expected, meanwhile the solid-state synthesis affords a green, rapid, and scalable pathway to Co@OMC catalysts.

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

Hydrotreatment of Nylon 66 and Amide Model Compounds Over Sulfided NiMo Catalysts

Molybdenum sulfide-based catalysts, such as nickel–molybdenum on alumina (NiMoS x /Al 2 O 3 ), are widely used in hydrotreating and have potential for catalyzing waste plastic conversion via hydrogenolysis, yet their performance, such as reaction kinetics and network, for amide-rich polymer feeds is poorly defined. Here we combine Nylon 66 with the amide model compound, N,N-dibutylhexanediamide (DBDAD), to quantify hydrodeoxygenation (HDO) and hydrodenitrogenation (HDN) chemistry in a stirred batch reactor (53 bar H 2 , 280–320°C). DBDAD conversion is near-linear with time, indicating strong adsorption of the substrates on the active sites. Time-resolved product identification indicates parallel C─O first-cleavagedeoxygenation (DO) and C─N first-cleavagedenitrogenation (DN) sequences proceeding through amine and diol intermediates, respectively, to C 4 ─C 6 alkanes. Increasing temperature shifts selectivity toward DN, decreasing the initial r(DO)/r(DN) from 1.38 (280°C) to 0.69 (320°C), with an apparent activation energy of 173 kJ mol −1 for DBDAD conversion. At 300°C, nylon 66 converts faster than DBDAD, producing a complex mixture of oxygen- and nitrogen-containing species and an initial rate ratio r(DO)/r(DN) of 1.6. No heteroaromatic nitrogen products are detected by the method used. These results provide reaction pathways and product signatures relevant to hydro-processing catalysts exposed to polyamide-derived streams.

Nylon 66↗
DOE OSTI2015

Back Cover: Highly Selective Condensation of Biomass-Derived Methyl Ketones as a Source of Aviation Fuel (ChemSusChem 10/2015)

The Back Cover shows a depiction of the carbon cycle for a tunable set of chemistry that can be used to synthesize exceptional jet fuel via n -alkyl methyl ketones. Here, methyl ketones, which can be derived from biomass in either chemical or hybrid biological-chemical pathways, are selectively transformed to cyclic trimers by aldol condensation and Michael addition. By altering the ratio of starting methyl ketones, an alkane blend can be generated after hydrodeoxygenation that not only satisfies the low freezing point necessary for jet fuel, but also the broad volatility distribution typical of petroleum-derived fuels. The carbon generated by combustion of these fuels then produces further biomass, completing the carbon cycle. More details can be found in the Full Paper by Sacia etal. (DOI: 10.1002/cssc.201500002).

biofuels↗
DOE OSTI2015

Upgrading Lignocellulosic Products to Drop-In Biofuels via Dehydrogenative Cross-Coupling and Hydrodeoxygenation Sequence

Life-cycle analysis (LCA) allows the scientific community to identify the sources of greenhouse gas (GHG) emissions of novel routes to produce renewable fuels. Herein, we integrate LCA into our investigations of a new route to produce drop-in diesel/jet fuel by combining furfural, obtained from the catalytic dehydration of lignocellulosic pentose sugars, with alcohols that can be derived from a variety of bio- or petroleum-based feedstocks. As a key innovation, we developed recyclable transition-metal-free hydrotalcite catalysts to promote the dehydrogenative cross-coupling reaction of furfural and alcohols to give high molecular weight adducts via a transfer hydrogenation-aldol condensation pathway. Subsequent hydrodeoxygenation of adducts over Pt/NbOPO 4 yields alkanes. Finally, implemented in a Brazilian sugarcane biorefinery such a process could result in a 53-79% reduction in life-cycle GHG emissions relative to conventional petroleum fuels and provide a sustainable source of low carbon diesel/jet fuel.

greenhouse gas↗
DOE OSTI2016

The Conversion of Starch and Sugars into Branched C 10 and C 11 Hydrocarbons

Oligosaccharides, such as starch, cellulose, and hemicelluloses, are abundant and easily obtainable bio-derived materials that can potentially be used as precursors for fuels and chemical feedstocks. To access the pertinent molecular building blocks (i.e., 5- or 6-carbon containing sugar units) located within these biopolymers and transform them into useful fuel precursors, oligosaccharide depolymerization followed by chain extension is required. This chain extension can readily be performed via a Garcia–Gonzalez-like approach using β-diketones under mild conditions to provide fuel precursors containing an increased carbon atom content that meets fuel requirements. In a subsequent step, ring opening and hydrodeoxygenation chemistry of these species allows for the preparation of branched alkanes under relatively mild conditions. Finally, this approach can be applied to monomeric sugars (glucose and xylose), oligosaccharides (starch), and potentially to hydrolyzed dedicated energy crops to allow the conversion of real biomass into fuel type molecules.

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

Simultaneous Upgrading of Furanics and Phenolics through Hydroxyalkylation/Aldol Condensation Reactions

The simultaneous conversion of cyclopentanone and m-cresol has been investigated on a series of solid-acid catalysts. Both compounds are representative of biomass-derived streams. Cyclopentanone can be readily obtained from sugar-derived furfurals through Piancatelli rearrangement under reducing conditions. Cresol represents a family of phenolic compounds, typically obtained from the depolymerization of lignin. In the first biomass conversion strategy proposed here, furfural is converted in high yields and selectivity to cyclopentanone (CPO) over metal catalysts such as Pd-Fe/SiO 2 at 600 psi (~4.14 MPa) H 2 and 150 °C. Subsequently, CPO and cresol are further converted through acid-catalyzed hydroxyalkylation. This C-C coupling reaction may be used to generate products in the molecular weight range that is appropriate for transportation fuels. As molecules beyond this range may be undesirable for fuel production, a catalyst with a suitable porous structure may be advantageous for controlling the product distribution in the desirable range. If Amberlyst resins were used as a catalyst, C 12 –C 24 products were obtained whereas when zeolites with smaller pore sizes were used, they selectively produced C 10 products. Alternatively, CPO can undergo the acid-catalyzed self-aldol condensation to form C 10 bicyclic adducts. As an illustration of the potential for practical implementation of this strategy for biofuel production, the long-chain oxygenates obtained from hydroxyalkylation/aldol condensation were successfully upgraded through hydrodeoxygenation to a mixture of linear alkanes and saturated cyclic hydrocarbons, which in practice would be direct drop-in components for transportation fuels. Aqueous acidic environments, which are typically encountered during the liquid-phase upgrading of bio-oils, would inhibit the efficiency of base-catalyzed processes. Therefore, the proposed acid-catalyzed upgrading strategy is advantageous for biomass conversion in terms of process simplicity.

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

Kinetic and thermodynamic study of the reduction of 1,1-diphenylethylene by a thermally frustrated diethyl ether-BCF Lewis pair

The reaction enthalpy and rate of reduction of 1,1-diphenylethylene (DPE) by the Frustrated Lewis pair formed between tris-pentafluorophenylborane (BCF) and diethyl ether (Et₂O) in dichloromethane have been determined by mixing calorimetry. At 50 °C and 13.6 atm hydrogen a 0.08 M solution of DPE is reduced to 1,1-diphenylethane in the presence of 1 equivalent BCF and 0.8 equivalents Et₂O in 40 minutes. NMR spectroscopy showed >99% conversion to the reduced product. The rate of conversion of the olefin to the alkane as monitored by the time dependent heat flow showed a linear dependence on the free Et₂O and BCF concentration. Integration of the heat flux provides a measure of the reaction enthalpy of ΔH ca. -116±4 kJ/mol for the reaction Ph₂C=CH₂+H2→Ph₂CHCH₃. The equilibrium constant for dative adduct formation, Et₂O+BCF↔Et₂O—BCF, was determined as a function of temperature by ¹⁹F NMR spectroscopy and provided an experimental measure of the enthalpy, ΔH = -54.6±3.3 kJ/mol⁻¹ and entropy, ΔS=-154±13 Jmol⁻¹ K⁻¹, for dative bond formation in DCM. Extrapolation of the van’t Hoff plot to 50 ºC provides K eq that is used to estimate the concentration of free BCF and Et₂O available to activate hydrogen. This work was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle.

Whittemore, Sean M.↗
DOE OSTI2020

Reaction mechanisms of a cyclic ether intermediate: Ethyloxirane

Oxiranes are a class of cyclic ethers formed in abundance during low-temperature combustion of hydrocarbons and biofuels, either via chain-propagating steps that occur from unimolecular decomposition of β -hydroperoxyalkyl radicals ( β -˙QOOH) or from reactions of HOÓ with alkenes. Ethyloxirane is one of four alkyl-substituted cyclic ether isomers produced as an intermediate from n -butane oxidation. While rate coefficients for β -˙QOOH → ethyloxirane + ÓH are reported extensively, subsequent reaction mechanisms of the cyclic ether are not. As a result, chemical kinetics mechanisms commonly adopt simplified chemistry to describe ethyloxirane consumption by convoluting several elementary reactions into a single step, which may introduce mechanism truncation error—uncertainty derived from missing or incomplete chemistry. Here we provide fundamental insight on reaction mechanisms of ethyloxirane in support of ongoing efforts to minimize mechanism truncation error. Reaction mechanisms are inferred from the detection of products during chlorine atom-initiated oxidation experiments using multiplexed photoionization mass spectrometry conducted at 10 Torr and temperatures of 650 K and 800 K. To complement the experiments, calculations of stationary point energies were conducted using the ccCA-PS3 composite method on ˙R + O 2 potential energy surfaces for the four ethyloxiranyl radical isomers, which produced barrier heights for 24 reaction pathways. In addition to products from ˙QOOH → cyclic ether + ÓH and ˙R + O 2 → conjugate alkene + HOÓ, both of which were significant pathways and are prototypical to alkane oxidation, other species were identified from ring-opening of both ethyloxiranyl and ˙QOOH radicals. The latter occurs when the unpaired electron is localized on the ether group, causing the initial ˙QOOH structure to ring-open and form a resonance-stabilized ketohydroperoxide-type radical. The present work provides the first analysis of ethyloxirane oxidation chemistry, which reveals that consumption pathways are complex and may require an expansion of submechanisms to increase the fidelity of chemical kinetics mechanisms.

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

Modeling the Effects of Trimethylsilanol on Syngas Combustion Kinetics

A perturbation analysis modeling approach based on a genetic algorithm was used to identify possible reaction pathways to explain previous experimental observations of the strong acceleration of syngas auto-ignition by trimethylsilanol (TMSO). Organosilicon reactions were taken from an existing chemical kinetic mechanism for tetramethylsilane pyrolysis which also contained TMSO reactions. The experimental targets for optimization were ignition delay times and peak OH radical concentrations in the range 1010–1070 K, 5 atm with dilute (4%) ϕ = 0.1 syngas mixtures in N 2 /Ar containing 0, 200, and 1000 ppm TMSO. Hundreds of thousands of trials resulted in three models which accurately predicted the experimental auto-ignition times and peak OH concentrations. Rate of production analyses indicated that TMSO forms dimethylsilanediol, which then reacts creating two “catalytic loops.” The net effect of the loops is to accelerate the reaction H 2 + O = OH + H at a faster effective rate than H 2 /O 2 kinetics alone, thus enhancing the reactivity of syngas. The formation of the loops may be attributable to the high Si–C bond energies in siloxanols, reducing rates of thermal decomposition and allowing dimethylsilanediol to react with H 2 for a longer duration compared with its alkane analog. Here, the results of the current work provide valuable direction for fundamental studies of these new hypothesized reaction pathways.

Mansfield, Andrew B. [Eastern Michigan University,↗
DOE OSTI2019

Ball Milling Modified SAPO‐11 Based Catalysts for n ‐Decane Hydroisomerization

Abstract Bifunctional Pt/SAPO‐11 catalysts were prepared using as acid matrix the microporous silico‐aluminophosphate, SAPO‐11, synthesized under microwave radiation. After synthesis, the material was physically modified using a ball mill, changing the grinding time but keeping frequency constant. The metal function (0.5 wt.% Pt) was introduced through mechanical mixture with commercial Pt loaded alumina. The catalysts were characterized by several techniques: powder X‐Ray Diffraction, pyridine adsorption followed by infrared spectroscopy, low temperature N 2 adsorption, Hg intrusion porosimetry and electronic microscopy (SEM). The characterization data show modifications of structural and textural properties of the samples as the milling time increases. The catalytic behaviour of Pt/SAPO‐11 materials was studied for hydroisomerization of long chain n ‐alkanes, using n ‐decane as model molecule, aiming to increase the production of mono‐branched isomers. The catalytic results show that, under optimized milling conditions (60 min; 50 Hz) the selectivity into mono‐branched isomers increased when compared with parent catalyst.

Ferreira, Luisa↗
DOE OSTI2023

Genesis of Active Pt/CeO 2 Catalyst for Dry Reforming of Methane by Reduction and Aggregation of Isolated Platinum Atoms into Clusters

Atomically dispersed metal catalysts offer the advantages of efficient metal utilization and high selectivities for reactions of technological importance. Such catalysts have been suggested to be strong candidates for dry reforming of methane (DRM), offering prospects of high selectivity for synthesis gas without coke formation, which requires ensembles of metal sites and is a challenge to overcome in DRM catalysis. However, investigations of the structures of isolated metal sites on metal oxide supports under DRM conditions are lacking, and the catalytically active sites remain undetermined. Data characterizing the DRM reaction-driven structural evolution of a cerium oxide- supported catalyst, initially incorporating atomically dispersed platinum, and the corresponding changes in catalyst performance are reported. X-ray absorption and infrared spectra show that the reduction and agglomeration of isolated cationic platinum atoms to form small platinum clusters/nanoparticles are necessary for DRM activity. Density functional theory calculations of the energy barriers for methane dissociation on atomically dispersed platinum and on platinum clusters support these observations. Here the results emphasize the need for in-operando experiments to assess the active sites in such catalysts. The inferences about the catalytically active species are suggested to pertain to a broad class of catalytic conversions involving the rate-limiting dissociation of light alkanes.

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

Droplet Evaporation-Based Approach for Microliter Fuel Property Measurements

Small-volume, high-throughput screening techniques are sought to enable downselection from a large candidate pool of bio-blendstocks to a select few, having physical properties consistent with requirements of downsized, turbo-boosted internal combustion engines. Herein, this work presents a droplet evaporation-based approach to predict heat of vaporization, vapor pressure, diffusion coefficient, and Lennard–Jones parameters for an unknown fuel. Two different schemes, considering the isothermal evaporation of a moving droplet in ambient air, are proposed, which combine droplet velocity and temperature measurements, with some known properties to predict unknown properties. The schemes utilize an inverse solution of a transient model of droplet evaporation solved in an iterative fashion. A baseline scheme, which only requires droplet size change measurements, is evaluated using test data for three liquid fuels, comprising of alkanes and alcohols, as obtained in a temperature-controlled chamber. Results yield temperature-dependent heat of vaporization and vapor pressure predictions within 10 % and 22 %, respectively, of reference values. The advanced scheme, which additionally requires droplet temperature measurement, is numerically evaluated in the current work and will be experimentally validated in future efforts. The advanced scheme is found to significantly improve prediction quality, with deviations less than 2 % and 1 % for heat of vaporization and vapor pressure, while also predicting diffusion coefficient and Lennard–Jones parameters within 5 % and 8 %, respectively. The combined set of approaches, which primarily track droplet evaporation, can be incorporated into a small-volume, high-throughput fuel screening process.

09 BIOMASS FUELS↗