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At least 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Enhanced Selectivity for C 2 H 4 Production from C 2 H 6 on Partially Chlorinated IrO 2 (110) Surfaces

Modifying metal oxide surfaces to limit their oxidizing activity can provide a means of improving catalytic selectivity toward the partial oxidation of light alkanes. Here, in this study, we investigated the oxidation of C 2 H 6 on Cl-modified IrO 2 (110) surfaces using temperature-programmed reaction spectroscopy (TPRS) and first-principles microkinetic modeling. We find that substituting Cl for O in the IrO 2 (110) surface enhances the selectivity for C 2 H 6 conversion to C 2 H 4 during TPRS by suppressing extensive oxidation to CO x products, while also either enhancing C 2 H 4 production or altering it to a lesser extent, depending on the initial C 2 H 6 coverage. The C 2 H 4 selectivity increased with increasing C 2 H 6 and Cl coverage, but reached a limiting value below 50%. The Cl coverage changed negligibly during C 2 H 6 oxidation, and the surface reactivity decreased only marginally for Cl coverages up to 0.5 ML (monolayer). TPRS simulations using a microkinetic model predict C 2 H 4 and CO x product yields as a function of the Cl coverage that agree closely with the experimental results. According to the simulations, C 2 H 6 conversion to C 2 H 4 occurs on Cl-IrO 2 (110) by the hydrogenation of C 2 H 3 * species adsorbed in blocked states, in which neighboring sites are occupied only by unreactive HO and Cl species. The microkinetic modeling shows that H-hopping away from surface HO groups provides a relatively efficient route for C 2 H 3 * to escape blocked configurations and dehydrogenate, and that this process can limit the C 2 H 4 selectivity on Cl-IrO 2 (110) under the conditions studied. Overall, our results demonstrate that Cl-substitution into IrO 2 (110) enhances the selectivity for C 2 H 4 production from C 2 H 6 and provides insights into the reaction mechanism that can guide strategies to further improve the C 2 H 4 selectivity.

IrO2↗
DOE OSTI2016

The promotional effects of cesium promoter on higher alcohol synthesis from syngas over cesium-promoted Cu/ZnO/Al2O3 catalysts

In this study, the promotional effects of cesium promoter on higher alcohol (C2+OH) synthesis from syngas over Cs-Cu/ZnO/Al2O3 catalysts were investigated using a combined experimental and theoretical density functional theory (DFT) calculation method. In the presence of cesium, the C2+OH productivity increases from 77.1 g•kgcat-1•h-1 to 157.3 g•kgcat-1•h-1 at 583 K due to the enhancement of the initial C–C bond formation. Detailed analysis of chain growth probabilities (CGPs) confirms that initial C–C bond formation is the rate-determining step in the temperature range of 543-583 K. Addition of cesium promoter significantly increases the productivities of 2-methyl-1-propanol, while the CGPs values (C3* to 2-methyl-C3*) is almost unaffected. With the assistance of cesium promoter, the CGPs of the initial C–C bond formation step (C1* to C2*) could be increased from 0.13 to 0.25 at 583 K. DFT calculations indicate that the initial C–C bond formation is mainly contributed by the HCO+HCO coupling reaction over the ZnCu(211) model surface. In the presence of the Cs2O, the stabilities of key reaction intermediates such as HCO and H2CO are enhanced which facilitates both HCO+HCO and HCO+H2CO coupling reaction steps with lower activation barriers over the Cs2O-ZnCu(211) surface. The promotional effects of cesium on the C2+OH productivity are also benefited from the competitive CH+HCO coupling reaction over CH hydrogenation that leads to lower alkane formation. In addition, Bader charge analysis suggests that the presence of cesium ions would facilitate the nucleophilic reaction between HCO and H2CO for initial C–C bond formation. This work was supported by the National Natural Science Foundation of China (No. 91545114 and No. 91545203). We appreciate the joint PhD scholarship support from the China Scholarship Council. The authors would also like to thank the support from Collaborative Innovation Center of Chemistry for Energy Materials (2011-iChEM). DM was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences. Computing time was granted by the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL). EMSL is a national scientific user facility located at Pacific Northwest National Laboratory (PNNL) and sponsored by DOE’s Office of Biological and Environmental Research. PNNL is a multiprogram national laboratory operated for DOE by Battelle Memorial Institute. We also appreciate the support from Sinochem Quanzhou Petrochemical Co. Ltd.

cesium↗
DOE OSTI2016

Quantum Mechanical Screening of Single-Atom Bimetallic Alloys for the Selective Reduction of CO 2 to C 1 Hydrocarbons

Electrocatalytic reduction of CO 2 to energy-rich hydrocarbons such as alkanes, alkenes, and alcohols is a very challenging task. So far, only copper has proven to be capable of such a conversion. Here, we report density functional theory (DFT) calculations combined with the Poisson-Boltzmann implicit solvation model to show that single-atom alloys (SAAs) are promising electrocatalysts for CO 2 reduction to C 1 hydrocarbons in aqueous solution. The majority component of the SAAs studied is either gold or silver, in combination with isolated single atoms, M (M = Cu, Ni, Pd, Pt, Co, Rh, and Ir), replacing surface atoms. We envision that the SAA behaves as a one-pot tandem catalyst: first gold (or silver) reduces CO 2 to CO, and the newly formed CO is then captured by M and is further reduced to C 1 hydrocarbons such as methane or methanol. We studied 28 SAAs, and found about half of them selectively favor the CO 2 reduction reaction over the competing hydrogen evolution reaction. Most of those promising SAAs contain M = Co, Rh, or Ir. The reaction mechanism of two SAAs, Rh@Au(100) and Rh@Ag(100), is explored in detail. Both of them reduce CO 2 to methane but via different pathways. For Rh@Au(100), reduction occurs through the pathway *CO → *CHO → *CHOH → *CH + H 2 O (l) → *CH 2 + H 2 O (l) → *CH 3 + H 2 O (l) → * + H 2 O (l) + CH 4(g) ; whereas, for Rh@Ag(100), the pathway is *CO → *CHO → *CH 2 O→ *OCH 3 → *O + CH 4(g) → *OH + CH 4(g) →* + H 2 O (l) + CH 4(g) . The minimum applied voltages to drive the two electrocatalytic systems are -1.01 and -1.12 V RHE for Rh@Au(100) and Rh@Ag(100), respectively, at which the Faradaic efficiencies for CO 2 reduction to CO are 60% for gold and 90% for silver. This suggests that SAA can efficiently reduce CO 2 to methane with as small as 40% loss to the hydrogen evolution reaction for Rh@Au(100) and as small as 10% for Rh@Ag(100). Lastly, we hope these computational results can stimulate experimental efforts to explore the use of SAA to catalyze CO 2 electrochemical reduction to hydrocarbons.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Dry Reforming of Ethane and Butane with CO 2 over PtNi/CeO 2 Bimetallic Catalysts

Dry reforming is a potential process to convert CO 2 and light alkanes into syngas (H 2 and CO), which can be subsequently transformed to chemicals and fuels. Here in this work, PtNi bimetallic catalysts have been investigated for dry reforming of ethane and butane using both model surfaces and supported powder catalysts. The PtNi bimetallic catalyst shows an improvement in both activity and stability as compared to the corresponding monometallic catalysts. The formation of PtNi alloy and the partial reduction of Ce 4+ to Ce 3+ under reaction conditions are demonstrated by in-situ Ambient Pressure X-ray Photoemission Spectroscopy (AP-XPS), X-ray Diffraction (XRD) and X-ray Absorption Fine Structure (XAFS) measurements. A Pt-rich bimetallic surface is revealed by Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) following CO adsorption. Combined in-situ experimental results and Density Functional Theory (DFT) calculations suggest that the Pt-rich PtNi bimetallic surface structure would weaken the binding of surface oxygenates/carbon species and reduce the activation energy for C-C bond scission, leading to an enhanced dry reforming activity.

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

Synthesis Gas Conversion over Rh-Mn-W x C/SiO 2 Catalysts Prepared by Atomic Layer Deposition

The catalytic conversion of synthesis gas to value-added oxygenates and light hydrocarbons was studied here on Rh and Rh–Mn clusters on tungsten carbide-overcoated silica (W x C/SiO 2 ) at 523 K, 580 psi, and CO/H 2 = 1/1. The W x C-modified SiO 2 support was prepared by the overcoating of WO x on SiO 2 using atomic layer deposition (ALD) followed by carburization. The reactivities of Rh/W x C/SiO 2 catalysts with varying number of ALD cycles (number of cycles = 2, 5, 10, 20, and 30) were measured and showed that 5 ALD cycles of WxC suppressed the formation of methane. All W x C-modified catalysts showed enhancement in selectivity toward methanol and ethanol through CO hydrogenation and acetaldehyde hydrogenation, respectively. These catalysts also improved the overall turnover frequency (TOF). The addition of Mn species further promoted the activity and the selectivity toward ethanol and C 2+ hydrocarbons, especially light alkenes. The best performing Rh-2Mn/5cycle-W x C/SiO 2 catalyst (Rh:Mn molar ratio = 1:2) achieved 84.7% selectivity toward valuable oxygenates and C 2+ hydrocarbons with a ratio of alkenes to alkanes equal to 1.7, compared to Rh/SiO 2 which exhibited 80.4% selectivity toward the products aforementioned with a ratio of 0.5. The overall TOF was 20 times higher than that over Rh/SiO 2 (i.e., 5.6 × 10 –2 s –1 vs 2.9 × 10 –3 s –1 ). X-ray diffraction revealed that the existence of W 2 C, which was the dominant phase in Rh/5cycle-W x C/SiO 2 , favored the suppression of methane and enhanced the production of alcohols and C 2+ hydrocarbons compared to the WC support. Density functional theory calculations for Rh 19 , Rh 31 , and Rh 37 clusters on various WC surfaces suggested that the shape of Rh clusters is condition dependent and subject to H 2 pressure. The C- and O- binding energies on various sites for the clusters were used with scaling relations to probe their catalytic activity. With the use of this approach, the increase in the O binding energy when moving from the SiO 2 -supported Rh 37 cluster to the WC-supported cluster leads to an increase in the activity of Rh/W x C/SiO 2 at the expense of the reduction in the number of sites that are selective toward C 2 oxygenates.

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

Cooperative H 2 Activation across a Metal–Metal Multiple Bond and Hydrogenation Reactions Catalyzed by a Zr/Co Heterobimetallic Complex

In the quest for active and selective catalysts featuring nonprecious metals, bimetallic cooperativity poses a unique opportunity to promote catalytic reactions and influence selectivity. While examples of stoichiometric H 2 activation across metal–metal bonds have been reported, there have been limited advances toward the incorporation of a well-defined cooperative bimetallic H 2 activation process into a catalytic cycle for the hydrogenation of unsaturated hydrocarbons. We demonstrate that facile activation of H 2 by two nonprecious metals is facilitated by metal–metal cooperativity in the coordinatively unsaturated Zr/Co bis(phosphinoamide) complexes (THF)(I)Zr(XylNP i Pr 2 ) 2 CoPR 3 (3-PMe 3 and 3-PMePh 2 , Xyl =3,5-dimethylphenyl), which feature highly polar Zr–Co triple bonds. Owing to the stabilizing nature of the metal–metal bond, the H 2 activation products (THF)(I)Zr(μ-H)(XylNP i Pr 2 ) 2 Co(H)(PR 3 ) (4-PMe 3 and 4-PMePh 2 ), which feature one terminally bound Co hydride and one hydride bridging the two metals, have been isolated and crystallographically characterized. The Zr/Co bimetallic complex 3-PMePh 2 is an active catalyst for the hydrogenation of alkenes and semihydrogenation of alkynes, and relevant intermediates including 4-PMePh 2 and alkene (5) and alkyne (6) adducts have been identified spectroscopically in situ and isolated and characterized through independent synthesis. The alkyne semihydrogenation reaction catalyzed by 3-PMePh 2 exhibits high selectivity for alkene over alkane products and generates an unselective distribution of (E)- and (Z)-alkenes via direct formation of both stereoisomers. These findings lend insight into the roles that metal–metal bonding and cooperativity play in the activation of small molecules and the promotion and selectivity of subsequent catalytic transformations.

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

Quantum Chemical Characterization of Structural Single Fe(II) Sites in MIL-Type Metal–Organic Frameworks for the Oxidation of Methane to Methanol and Ethane to Ethanol

Single non-heme Fe(II) ions present as structural moieties in several metal–organic frameworks (e.g., MIL-100, MIL-101, and MIL-808, where MIL indicates Materials of Institute Lavoisier) are identified by Kohn–Sham density functional calculations as promising catalysts for C–H bond activation, with energetic barriers as low as 40 kJ mol–1 for ethane and 60 kJ mol –1 for methane following the oxidative activation of iron. The rate-determining step is the activation of N 2 O and has a barrier of 140 kJ mol –1 . Through consideration of the full reaction profile leading to the corresponding alcohols, ethanol and methanol, we have identified key changes in the chemical composition of the node that would modulate catalytic activity. The thermal and chemical stabilities of these materials, together with the scalability of their syntheses, make them attractive catalysts for the selective low-temperature conversion of light alkanes to higher-value oxygenates.

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

Identification of a Pt 3 Co Surface Intermetallic Alloy in Pt–Co Propane Dehydrogenation Catalysts

Bimetallic Pt-Co nanoparticles (NPs) were prepared and characterized by scanning transmission electron microscopy, in situ X-ray absorption spectroscopy, in situ synchrotron X-ray diffraction, and catalytic conversion for propane dehydrogenation with and without added H-2. In addition, the surface extended X-ray absorption fine structure (EXAFS) obtained by fitting the difference spectrum between the fully reduced and room-temperature-oxidized catalysts suggest that the surface structure remains Pt 3 Co, although the core changes from Pt to Pt 3 Co and to PtCo. At low Co loading, the bimetallic nanoparticles form a Pt3Co intermetallic surface alloy with Pt-rich core. With increasing Co loading, a full alloy forms where both the surface and NP compositions are Pt 3 Co. A further increase in Co loading leads to a Co-rich NP core, likely PtCo, with a surface of Pt 3 Co. Although Pt-Co intermetallic alloys form two different phases and several morphologies, the surface structures are similar in all catalysts. Although both monometallic Pt and Co are active for alkane dehydrogenation, all bimetallic Pt-Co catalysts are significantly more olefin selective than either single metal. The turnover rates of the bimetallic catalysts indicate that Pt is the active atom with little contribution from Co atoms. The high olefin selectivity is suggested to be due to Co acting as a less active structural promoter to break up large Pt ensembles in bimetallic NPs.

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

Competing Mechanisms in CO Hydrogenation over Co-MnOx Catalysts

We study the hydrogenation of CO under ambient pressure conditions over a Co-MnOx model catalyst using chemical transient kinetics (CTK) under calibrated molecular flow conditions. Alkanes and alkenes are shown to form with markedly differing kinetics. Quantitation of the data allows accumulating carbon and oxygen coverages to be determined at any instant of the “buildup” transients. Anderson-Schulz-Flory (ASF) chain lengthening probabilities are evaluated while approaching the steady-state of the reaction. A linear dependence of these probabilities on the transient CO gas pressure provides evidence for a CO insertion mechanism being in operation under high-coverage conditions. A detailed kinetic analysis of reactant/product formation and scavenging is in agreement with this conclusion. However, for coverages below the monolayer limit, fast CO dissociation, probably hydrogen-assisted and promoted by Mn2+, also enables significant CHx-CHy coupling to occur. Evidence was obtained from high resolution transmission electron microscopy (HRTEM) that a phase transition from Co to Co2C was triggered under atmospheric pressure conditions for the Co-MnOx catalyst.

Athariboroujeny, Motahare↗
DOE OSTI2019

Mechanistic Aspects of a Surface Organovanadium(III) Catalyst for Hydrocarbon Hydrogenation and Dehydrogenation

Understanding the mechanisms of action for base metal catalysis of transformations typically associated with precious metals is essential for the design of technologies for a sustainable energy economy. Isolated transition-metal and post-transition-metal catalysts on oxides such as silica are generally proposed to effect hydrogenation and dehydrogenation by a mechanism featuring either σ-bond metathesis or heterolytic bond cleavage as the key bond activation step. In this work, an organovanadium(III) complex on silica, which is a precatalyst for both olefin hydrogenation and alkane dehydrogenation, is interrogated by a series of reaction kinetics and isotopic labeling studies in order to shed light on the operant mechanism for hydrogenation. The kinetic dependencies of the reaction components are potentially consistent with both the σ-bond metathesis and the heterolytic bond activation mechanisms; however, a key deuterium incorporation experiment definitively excludes the simple σ-bond metathesis mechanism. Alternatively, a two-electron redox cycle, rarely invoked for homologous catalyst systems, is also consistent with experimental observations. Evidence supporting the formation of a persistent vanadium(III) hydride upon hydrogen treatment of the as-prepared material is also presented.

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

Spectroscopic Investigation of the High-Pressure Behavior of Aliphatic Hydrocarbon: Implications for Planetary Processes

Octadecane (C 18 H 38 ) is an aliphatic hydrocarbon that is abundant in carbonaceous chondritic meteorites. It is debated whether these hydrocarbons found in the meteorite are pristine or are a result of subsequent modifications as these meteorites are delivered to the Earth. It is well-known that meteorites are often subjected to extreme pressures and temperatures upon entering the Earth’s atmosphere. To explore the behavior of octadecane at high pressures, that is, how its molecular structure responds to compression, we use a diamond anvil cell in conjunction with Raman spectroscopy. Here, we find that at room temperatures, upon compression to ~5 GPa, a linear-chain octadecane molecule transforms into a bent-chain configuration. Similar transitions from linear to a bent configuration in other hydrocarbons have been documented. We find a linear correlation between the transition pressure from linear to bent configuration, and the chain length of the alkane, that is, longer chain lengths, is likely to be less stable in the linear configuration under compression. These kinks in the bent-chain configuration are likely sites for the dissociation of the longer chain hydrocarbons to smaller hydrocarbons. The octadecane sample examined in this study did not undergo any additional transition to the highest pressure (~18 GPa) explored in this study.

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

Henry’s Solubility and Diffusion Coefficients for 29 Volatile Organic Compounds in Polydimethylsiloxane Sylgard 184 at 293 K

Two-dimensional (2D) inverse gas chromatography (IGC) enables simultaneous determination of Henry’s solubility and Fickian diffusion coefficients for volatile organic compounds (VOCs) in polymer films. This technique offers a significant advantage over traditional cylindrical column IGC by providing precise control and measurement of the film thickness (here, 0.064 ± 0.002 mm), which is the critical length scale for accurate diffusivity determination. We apply this methodology to characterize VOC transport in Sylgard 184, a widely used polydimethylsiloxane (PDMS)-based polymer containing substantial silica filler content. At room temperature (20 °C), we measured solubility and diffusion coefficients for 29 common VOCs spanning diverse chemical functionalities, including alkanes, aromatics, chlorinated solvents, ketones, esters, and alcohols. Comparison with literature data for pure PDMS reveals that VOC solubility in Sylgard 184 is generally higher; for most non-hydrogen-bonding compounds it remains within a factor of 2 of pure PDMS, whereas alcohols are enhanced by roughly 1.8 to 3.7 times, which we attribute to favorable interactions with residual silanol groups on the silanized silica filler. Diffusion coefficients range from 1.0 × 10 –6 cm 2 /s (n-undecane) to 8.9 × 10–5 cm 2 /s (acetonitrile) and align well with extrapolated literature values for PDMS. This study provides essential thermodynamic and transport data for predicting VOC permeation in Sylgard 184 while demonstrating the utility of 2D IGC as a robust technique for characterizing rubbery polymer membranes across diverse industrial applications.

organic↗
DOE OSTI2024

Butene-Rich Alkene Formation from 2,3-Butanediol through Dioxolane Intermediates

The cost-effective production of sustainable aviation fuels (SAF) remains a major challenge within the energy sector. One approach to address this is the fermentation of biomass feedstocks into oxygenates followed by catalytic conversion to alkenes or other oligomerization precursors. 2,3-Butanediol (BDO) is a promising fermentation product due to its four-carbon nature, its decreased microorganism toxicity and associated higher maximum fermentation titers relative to other alcohols and oxygenates, and its capacity to be readily converted into butene isomers and longer chain alkenes. BDO conversion is currently constrained by separation challenges for BDO isolation due to its high boiling point and hydrophilicity. Here, this work expands upon previous BDO reactive separation via dioxolane formation over a solid acid catalyst by investigating the conversion of dioxolanes into alkene mixtures. Dioxolanes were formed from a range of aldehydes and subsequently converted over a Cu/ZSM-5 catalyst (448–523 K) via an ether cleavage, hydrogenation, and dehydration reaction network to form alkene-rich product mixtures (96% C 3+ alkene yield, 523 K). This selectivity is greater than that of direct BDO conversion to alkenes over an identical catalyst (89%, 523 K). C 3+ alkene selectivity is maximized between 498 and 523 K at complete dioxolane conversion without significant alkene hydrogenation to alkanes. The alkene product distributions can be tailored via both aldehyde selection during dioxolane formation and the dioxolane conversion reaction temperature. Alkene mixtures from dioxolane conversion predominantly reflect the carbon chain length and stereochemistry of BDO and the initial aldehyde at or below 498 K, yet higher reaction temperatures yield alkene mixtures of similar carbon chain distributions, regardless of initial aldehyde selection. Deactivation of the Cu/ZSM-5 catalyst is observed for multiple steps of the overall reaction network but can be minimized by facilitating the complete dioxolane-to-alkene reaction network at temperatures of at least 498 K.

2,3-butanediol↗
DOE OSTI2016

Valorization of Waste Lipids through Hydrothermal Catalytic Conversion to Liquid Hydrocarbon Fuels with in Situ Hydrogen Production

We demonstrate hydrothermal (300 degrees C, 10 MPa) catalytic conversion of real waste lipids (e.g., waste vegetable oil, sewer trap grease) to liquid hydrocarbon fuels without net need for external chemical inputs (e.g., H2 gas, methanol). A supported bimetallic catalyst (Pt-Re/C; 5 wt % of each metal) previously shown to catalyze both aqueous phase reforming of glycerol (a triacylglyceride lipid hydrolysis coproduct) to H2 gas and conversion of oleic and stearic acid, model unsaturated and saturated fatty acids, to linear alkanes was applied to process real waste lipid feedstocks in water. For reactions conducted with an initially inert headspace gas (N2), waste vegetable oil (WVO) was fully converted into linear hydrocarbons (C15-C17) and other hydrolyzed byproducts within 4.5 h, and H2 gas production was observed. Addition of H2 to the initial reactor headspace accelerated conversion, but net H2 production was still observed, in agreement with results obtained for aqueous mixtures containing model fatty acids and glycerol. Conversion to liquid hydrocarbons with net H2 production was also observed for a range of other waste lipid feedstocks (animal fat residuals, sewer trap grease, dry distiller's grain oil, coffee oil residual). These findings demonstrate potential for valorization of waste lipids through conversion to hydrocarbons that are more compatible with current petroleum-based liquid fuels than the biodiesel and biogas products of conventional waste lipid processing technologies.

09 BIOMASS FUELS↗
DOE OSTI2026

Fe- and Ru-H-Mordenites for Polyethylene Upcycling: Insights from Thermo-Catalytic Pyrolysis and DFT Studies

Catalytic pyrolysis of polyethylene (PE) was performed using Fe- and Ru-impregnated H-mordenite (HM) catalysts to produce lighter hydrocarbons. Catalyst surface areas were analyzed by N 2 adsorption−desorption and acidity by NH 3 - TPD studies. Reducibility of metal from H 2 -TPR, experiments indicate multiple oxidation states of Fe due to higher H 2 consumption. The catalyst activity studies monitored by GC− MS analysis highlight the importance of temperature and PE: catalyst ratio in optimizing hydrocarbon selectivity to C 1 −C 4 alkanes and C 2 −C 5 olefins. Studies with polymer-to-catalyst ratios of 1:1 and 1:2 at higher temperature increased PE conversion with stronger acid sites favoring conversion and moderate acid sites improving selectivity toward lighter olefins. While propane dominated at lower temperatures, propene was the main product at 500 °C. Both catalysts exhibited overall similar conversion, while Ru-HM yielded >40% propene selectivity compared to <40% for Fe-HM. Ethylene selectivity exceeded 10% in both cases. Density functional theory simulations using a C 4 surrogate on Ru-HM confirmed that late-stage cracking dominates dehydrogenation, validating the proposed reaction mechanism.

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

Isotopic Studies for Tracking Biogenic Carbon during Co-processing of Biomass and Vacuum Gas Oil

Co-processing bio-oils with petroleum-derived feeds in the existing multitrillion dollar refining and distribution infrastructure is an attractive option for introducing renewable energy into the fuels marketplace. Considerable research on co-processing bio-oils and vacuum gas oil (VGO) in fluid catalytic cracking units (FCC) using equilibrium catalysts (E-Cats) demonstrated that biomass-derived molecules decreased activity of and increased carbon laydown on E-Cat. In this work, 13 C-labeled biomass was co-processed with VGO using either an E-Cat or a proprietary zeolite Johnson Matthey catalyst (CP758), which is optimzed for upgrading biomass vapors in a riser reactor, to evaluate the fate of biogenic carbon in FCC products. The results from both catalysts indicate that biogenic carbon was incorporated into alkenes and aromatic hydrocarbons. While no biogenic carbon was found in linear alkanes, it was observed in cycloalkanes during experiments with E-Cat but not with CP758. All produced CO2 was biogenic as was most of the carbon laydown on the catalysts. Several partially deoxygenated biomass compounds, such as alkylphenols and benzofurans, unexpectedly contained small amounts of carbon from VGO. Although this study was conducted with labeled biomass and not bio-oil, it provides insights to reaction mechanisms for co-processing bio-oil and VGO in an FCC, which is required to develop catalysts that efficiently convert bio-oil components during FCC co-processing. This work also demonstrates that comprehensive catalyst development utilizing both biomass- and fossil-derived feeds is required to maximize the incorporation of biogenic carbon into transportation fuels.

09 BIOMASS FUELS↗
DOE OSTI2014

Molecular Characterization of Organosulfates in Organic Aerosols from Shanghai and Los Angeles Urban Areas by Nanospray-Desorption Electrospray Ionization High-Resolution Mass Spectrometry

Aerosol samples collected in the urban areas of Shanghai and Los Angeles were analyzed by nanospray-desorption electrospray ionization mass spectrometry (nano-DESI MS) with high mass resolution (m/Δm=100,000). Solvent mixtures of acetonitrile/water and acetonitrile/toluene were used to extract and ionize polar and non-polar compounds, respectively. A diverse mixture of oxygenated hydrocarbons, organosulfates, organonitrates, and organics with reduced nitrogen were detected in the Los Angeles sample. Majority of the organics in the Shanghai sample were detected as organosulfates. The dominant organosulfates in the two samples have distinctly different molecular characteristics. Specifically, organosulfates in the Los Angeles sample were dominated by isoprene- or monoterpene-derived products, while organosulfates of yet unknown origin in the Shanghai sample had distinctive characteristics of long aliphatic carbon chains and low degree of oxidation and unsaturation. The use of acetonitrile/toluene solvent facilitated identification of this type of organosulfates, suggesting they could be missed in previous studies relying on sample extraction using common polar solvents. The high molecular weight and low degree of unsaturation and oxidization of the organosulfates detected in the Shanghai sample suggest that they may act as surfactants, and plausibly affect the surface tension and hygroscopicity of the atmospheric particulate matter. We propose that direct esterification of carbonyl or hydroxyl compounds by sulfates or sulfuric acid in liquid phase could be the formation pathway of these special organosulfates. Finally, long-chain alkanes from vehicle emissions might be their precursors.

Environmental Molecular Sciences Laboratory↗