Experimental data for “Experimental and numerical study of variable oxygen index effects on soot yield and distribution in laminar co-flow diffusion flames”

<p>This bundle of files contains 2D maps of soot volume fractions and soot particle temperatures measured in methane/air coflow nonpremixed flames with varying ratios of oxygen to nitrogen in the oxidizer. These results are used in the paper “Experimental and numerical study of variable oxygen index effects on soot yield and distribution in laminar co-flow diffusion flames” by Abhishek Jain, Dhrubajyoti D. Das, Charles S. McEnally, Lisa D. Pfefferle and Yuan Xuan, which has been submitted to the 37th International Symposium on Combustion and is currently under review.</p> <p><br></p> <p>This material is based upon work supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Bioenergy Technologies Office (BETO) and Vehicle Technologies Office (VTO) Program Award Number DE-EE0007983. This work is also supported by the National Science Foundation (NSF) under Grant No. CBET 1604983. </p

Combustion of Methane over Palladium-Based Catalysts: Catalytic Deactivation and Role of the Support

Palladium-based catalysts supported on metal oxides are attractive for methane combustion at low temperature. However, at temperatures below 450 °C, their tendency to deactivate hinders their usefulness. Catalytic deactivation in this temperature regime has been attributed to a water/hydroxyl inhibition effect. We investigated this effect to better understand the mechanism for catalytic deactivation. Comparative in situ FTIR transmission spectroscopy experiments at 325 °C revealed that hydroxyl accumulation occurs on the oxide supports during catalytic methane combustion and deactivation. The water/hydroxyl accumulation on the support is slow to desorb at this temperature. In light of our recent finding that oxygen from the support is utilized in the methane combustion process, we propose that hydroxyl/water accumulation on the support impedes the catalytic combustion reaction by hindering oxygen mobility on the support. We support this hypothesis by demonstrating that the presence of water on the catalyst inhibits oxygen exchange with the oxide support

Sooting Tendencies of Nitrogenated Fuels

<p>Paper presented at the 2018 Spring Technical Meeting of the Eastern States Section of the Combustion Institute, March 4-7 2018, State College PA.</p> <p><br></p> <p>The sooting tendencies of over 30 nitrogen-containing hydrocarbons were measured and have been compared to analogous regular and oxygenated hydrocarbons.</p> <p><br></p

Synthesis and Raman Spectroscopy of Multiphasic Nanostructured Bi–Te Networks with Tailored Composition

Development of synthetic routes to control the morphology and composition of nanostructured thermoelectric materials and to leverage their unique performance enhancements presents challenges in the realization of practical thermoelectric systems. We report here the fabrication of intricate networks of nanostructured tellurium, bismuth telluride, and bismuth-rich compounds with diverse morphologies. The nanostructured networks synthesized via solution-phase techniques consist of nanocrystalline Bi₂Te₃ with a grain size of about 15–20 nm, 3–5 nm thick rolled-up nanosheets of Te forming tubular structures, nanotubes of Bi₂Te₃ about 300–400 nm in diameter, Te and Bi₄Te₃ nanowires ranging from 50 to 200 nm diameter, and microspheres of 3–7 μm diameter composed of self-assembled BiOCl nanorods. The formation and crystallinity of Bi-rich and Te-rich compounds were investigated using powder X-ray and electron back-scattered diffraction. We present the first detailed analysis of micro-Raman scattering of Bi_<i>x</i>Te_<i>y</i> nanostructures of above morphologies using six different laser wavelengths. The Bi_<i>x</i>Te_<i>y</i> nanostructures exhibit the most intense infrared (IR) active A_1u mode at 120 cm^–1 in the Raman spectra, which disperses with a change in the chemical composition and laser power. In addition, we observe new internal strain-induced peaks in the Raman spectra of Bi_<i>x</i>Te_<i>y</i> nanostructures. The rich morphologies and compositions present within the nanostructured Bi–Te compounds are expected to result in novel thermoelectric materials

Low-Temperature Carbon Capture Using Aqueous Ammonia and Organic Solvents

Current postcombustion CO₂ capture technologies are energy intensive, require high-temperature heat sources, and dramatically increase the cost of power generation. In this work, we introduce a new carbon capture process requiring significantly lower temperatures and less energy, creating further impetus to reduce CO₂ emissions from power generation. In this process, high-purity CO₂ is generated through the addition of an organic solvent (acetone, dimethoxymethane, or acetaldehyde) to a CO₂ rich, aqueous ammonia/carbon dioxide solution under room-temperature and -pressure conditions. The organic solvent and CO₂-absorbing solution are then regenerated using low-temperature heat. When acetone, dimethoxymethane, or acetaldehyde was added at a concentration of 16.7% (v/v) to 2 M aqueous ammonium bicarbonate, 39.8, 48.6, or 86.5%, respectively, of the aqueous CO₂ species transformed into high-purity CO₂ gas over 3 h. Thermal energy and temperature requirements for recovering acetaldehyde, the best-performing organic solvent investigated, and the CO₂-absorbing solution were 1.39 MJ/kg of CO₂ generated and 68 °C, respectively, 75% less energy than the amount used in a pilot chilled ammonia process and a temperature 53 °C lower. Our findings exhibit the promise of economically viable carbon capture powered entirely by abundant low-temperature waste heat

Realizing Comparable Oxidative and Cytotoxic Potential of Single- and Multiwalled Carbon Nanotubes through Annealing

The potential applications as well as the environmental and human health implications of carbon nanomaterials are well represented in the literature. There has been a recent focus on how specific physicochemical properties influence carbon nanotube (CNT) function as well as cytotoxicity. The ultimate goal is a better understanding of the causal relationship between fundamental physiochemical properties and cytotoxic mechanism in order to both advance functional design and to minimize unintended consequences of CNTs. This study provides characterization data on a series of multiwalled carbon nanotubes (MWNTs) that underwent acid treatment followed by annealing at increasing temperatures, ranging from 400 to 900 °C. These results show that MWNTs can be imparted with the same toxicity as single-walled carbon nanotubes (SWNTs) by acid treatment and annealing. Further, we were able to correlate this toxicity to the chemical reactivity of the MWNT suggesting that it is a chemical rather than physical hazard. This informs the design of MWNT to be less hazardous or enables their implementation in antimicrobial applications. Given the reduced cost and ready dispersivity of MWNTs as compared to SWNTs, there is a significant opportunity to pursue the use of MWNTs in novel applications previously thought reserved for SWNTs

High-Yield Hydrogen Production from Aqueous Phase Reforming over Single-Walled Carbon Nanotube Supported Catalysts

Pt and Pt–Co bimetallic catalysts supported on single-walled carbon nanotubes (SWNTs) were synthesized by a wet reduction–decoration method and tested for catalytic activity of aqueous phase reforming of ethylene glycol. The Pt decorated on SWNT achieves a catalyst mass time hydrogen yield of 890 micromole gcat^–1 min^–1, which is higher than the reported results for Pt–alumina catalyst. Experiments also show that this catalyst has better activity than Pt supported on activated carbon with a similar surface area, showing the advantage of SWNTs as a catalyst support. Factors affecting the aqueous phase reforming activity, such as temperature, pressure, WHSV, catalyst particle size, etc., were investigated. We have also explored Pt–Co bimetallic catalysts by combining the structural characterization results with the reactivity results and revealed that bimetallic catalysts may promote the catalyst performance in two different ways: either via the formation of Pt–Co alloy phase or via the synergistic catalytic activities of individual Pt and Co particles. The Pt–Co–SWNT catalyst achieved a hydrogen production activity as high as 4.6 mmol gcat^–1 min^–1

Chiral-Selective CoSO₄/SiO₂ Catalyst for (9,8) Single-Walled Carbon Nanotube Growth

Electronic and optical properties of single-walled carbon nanotubes (SWCNTs) correlate with their chiral structures. Many applications need chirally pure SWCNTs that current synthesis methods cannot produce. Here, we show a sulfate-promoted CoSO₄/SiO₂ catalyst, which selectively grows large-diameter (9,8) nanotubes at 1.17 nm with 51.7% abundance among semiconducting tubes and 33.5% over all tube species. After reduction in H₂ at 540 °C, the catalyst containing 1 wt % Co has a carbon yield of 3.8 wt %, in which more than 90% is SWCNT. As compared to other Co catalysts used for SWCNT growth, the CoSO₄/SiO₂ catalyst is unique with a narrow Co reduction window under H₂ centered at 470 °C, which can be attributed to the reduction of highly dispersed CoSO₄. X-ray absorption spectroscopy (XAS) results suggested the formation of Co particles with an average size of 1.23 nm, which matches the diameter of (9,8) tubes. Density functional theory study indicated that the diameter of structurally stable pure Co particles is scattered, matching the most abundant chiral tubes, such as (6,5) and (9,8). Moreover, the formation of such large Co particles on the CoSO₄/SiO₂ catalyst depends on sulfur in the catalyst. XAS results showed that sulfur content in the catalyst changes after catalyst reduction at different conditions, which correlates with the change in (<i>n</i>,<i>m</i>) selectivity observed. We proposed that the potential roles of sulfur could be limiting the aggregation of Co atoms and/or forming Co–S compounds, which enables the chiral selectivity toward (9,8) tubes. This work demonstrates that catalysts promoted with sulfur compounds have potentials to be further developed for chiral-selective growth of SWCNTs

Hydrophobic CuO Nanosheets Functionalized with Organic Adsorbates

A new class of hydrophobic CuO nanosheets is introduced by functionalization of the cupric oxide surface with <i>p</i>-xylene, toluene, hexane, methylcyclohexane, and chlorobenzene. The resulting nanosheets exhibit a wide range of contact angles from 146° (<i>p</i>-xylene) to 27° (chlorobenzene) due to significant changes in surface composition induced by functionalization, as revealed by XPS and ATR-FTIR spectroscopies and computational modeling. Aromatic adsorbates are stable even up to 250–350 °C since they covalently bind to the surface as alkoxides, upon reaction with the surface as shown by DFT calculations and FTIR and ¹H NMR spectroscopy. The resulting hydrophobicity correlates with H₂ temperature-programmed reduction (H₂-TPR) stability, which therefore provides a practical gauge of hydrophobicity

Sooting Tendencies of Aromatic Hydrocarbons with Oxygen-Containing Side-Chains

<p>Paper presented at the 2018 Spring Technical Meeting of the Eastern States Section of the Combustion Institute, March 4-7 2018, State College PA.</p> <p><br></p> <p>Yield Sooting Index (YSI) was determined for 13 oxygen-containing aromatic compounds by measuring line-of-sight spectral radiance (LSSR) in a laminar non-premixed methane/air flame doped with 1000 ppm of each compound. The compounds included anisole (methoxybenzene), other aromatic ethers, and phenols. The presence of oxygen greatly reduced soot formation in some cases, but increased it in others. Thus oxygenated aromatics are potentially valuable as fuel components with intrinsically low particulate emissions, but the specific structure is important. Compounds containing an aromatic ring with an adjacent oxygen atom tended to have a lower sooting tendency than did compounds with oxygen atoms elsewhere in the side chain. This observation was quantitatively explored using Density Functional Theory (DFT) calculations. The bond dissociation energies for nine aromatic hydrocarbons and oxygenates were calculated using GGA B3LYP density functions with 6-31G(d) basis sets. When possible, unimolecular dissociation to phenoxy radical was favored and resulted in much lower YSIs than similar compounds where the oxygen atom was not adjacent to the aromatic ring. Structures that dissociated to benzyl radical had much higher sooting tendencies, sometimes by over a factor of two in comparison to phenoxy-forming compounds.</p