Jason Street

Catalytic conversion wood syngas to synthetic aviation turbine fuels over a multifunctional catalyst.

A continuous process involving gasification, syngas cleaning, and Fischer-Tropsch (FT) synthesis was developed to efficiently produce synthetic aviation turbine fuels (SATFs). Oak-tree wood chips were first gasified to syngas over a commercial pilot plant downdraft gasifier. The raw wood syngas contains about 47% N(2), 21% CO, 18% H(2), 12% CO(2,) 2% CH(4) and trace amounts of impurities. A purification reaction system was designed to remove the impurities in the syngas such as moisture, oxygen, sulfur, ammonia, and tar. The purified syngas meets the requirements for catalytic conversion to liquid fuels. A multi-functional catalyst was developed and tested for the catalytic conversion of wood syngas to SATFs. It was demonstrated that liquid fuels similar to commercial aviation turbine fuels (Jet A) was successfully synthesized from bio-syngas.

Catalytic removal of oxygen from biomass-derived syngas

Selective oxygen (O2) removal from wood-derived syngas was investigated over three types of ceria-modified alumina supported metal catalysts (i.e., Pt, Pd, and Cu). Complete O2 removal was observed with the Pt and Pd catalysts at a lower temperature than with the Cu catalyst. Gas hourly space velocity (GHSV) was another critical parameter affecting O2 removal, substantially reducing O2 conversion by all three catalysts at 4000 h(-1) or above. The Cu catalyst appeared to be most sensitive to GHSV. Among three catalysts, the Pd catalyst had the best performance on O2 removal. In addition to reaction conditions, CO2 and water vapor in the syngas also influenced O2 removal, both of which had adverse effects on O2 conversion. Stability tests indicated that both Pt and Pd catalysts were quite stable over a 300 h testing period while the Cu catalyst was deactivated after 50h and regenerated by elevating reaction temperature.

Production of high-value products including gasoline hydrocarbons from the thermochemical conversion of syngas

This article reviews subjects dealing with the chemistry, catalytic poisoning, newer catalyst technologies and possible future solutions to increase the efficiency of creating high-value products by thermochemically converting gasified biomass (producer gas). This article puts emphasis on bi-functional catalysts containing transition metals coupled with zeolites for renewable-fuel production. High-value products such as gasoline-range hydrocarbons, dimethyl ether, aldehydes, isobutane, isobutene and other olefins can be produced with gasified biomass due to the gas containing syngas (H2 + CO). The chemistry and production of these chemicals are discussed in this article. The importance of certain process variables, such as temperature, space velocity, gas ratios, and pressure are discussed along with the importance of reactor design. The subject of the importance of the cleanliness of the producer gas, so that maximum high-value product yield can be achieved with the greatest efficiency, is also discussed.

Synthesis, mechanical investigation, and application of nitrogen and phosphorus co-doped carbon dots with a high photoluminescent quantum yield

Heteroatom-doped carbon dots (CDs) with a high photoluminescent quantum yield (PLQY) have recently attracted attention due to their applications in chemical sensors, photocatalysis, bioimaging, and drug delivery. Nitrogen and phosphorus are in close proximity to carbon in the periodic table and are key tracking elements in the field of biomedical imaging. These two elements alter the optical and electronic properties of CDs and help improve the fundamental understanding of their PLQY. This can also lead to multifunctional usage in photoimaging and photothermal therapy. However, most PLQYs resulting from the synthesis of P-doped CDs are currently below 50%. These CDs have limited usefulness in the fields of bioimaging and drug delivery. In this study, a single-step, high-efficiency hydrothermal method was applied to synthesize nitrogen and phosphorous-doped carbon dots ((N,P)-CDs) with a PLQY of up to 53.8% with independent emission behavior. Moreover, the CDs presented high monodispersity, robust excitation-independent luminescence, and stability over a large pH range. Spectroscopic investigations indicated that the PLQY of the (N,P)-CDs was primarily due to the addition of P and the passivation effect of the oxidized surface. The excellent fluorescence properties of (N,P)-CDs can be effectively and selectively quenched by Hg2+ ions. Such systems show a linear response in the 0–900 nM concentration range with a short response time, indicating their potential for applications in the fields of chemistry and biology.

Photoluminescence mechanism and applications of Zn-doped carbon dots

Heteroatom-doped carbon dots (CDs) with excellent optical characteristics and negligible toxicity have emerged in many applications including bioimaging, biosensing, photocatalysis, and photothermal therapy. The metal-doping of CDs using various heteroatoms results in an enhancement of the photophysics but also imparts them with multifunctionality. However, unlike nonmetal doping, typical metal doping results in low fluorescence quantum yields (QYs), and an unclear photoluminescence mechanism. In this contribution, we detail results concerning zinc doped CDs (Zn-CDs) with QYs of up to 35%. The zinc ion charges serve as a surface passivating agent and prevent the aggregation of graphene π–π stacking, leading to an increase in the QY of the Zn-CDs. Structural and chemical investigations using spectroscopic and first principle simulations further revealed the effects of zinc doping on the CDs. The robust Zn-CDs were used for the ultra-trace detection of Hg2+ with a detection limit of 0.1 μM, and a quench mechanism was proposed. The unique optical properties of the Zn-CDs have promise for use in applications such as in vivo sensing and future phototherapy applications.

High photoluminescence quantum yield of 18.7% by using nitrogen-doped Ti3C2 MXene quantum dots

Quantum dots, derived from two-dimensional (2D) materials, have shown promising applications in bioimaging, photocatalysis, biosensors and white light emission devices (W-LEDs). Herein, this work involves producing a high photoluminescence quantum yield (PLQY) for 2D transition metal carbide MXene (nitrogen-doped, N-doped Ti3C2) quantum dots using Ti3C2 as a precursor and ethylenediamine as a nitrogen source. The hydrothermally treated N-doped Ti3C2 quantum dots developed in this study have an average size of 3.4 nm and a PLQY of up to 18.7%, which is by far the highest QY reported to date. The mechanism of the enhanced PLQY of the N-doped Ti3C2 quantum dots is systematically discussed by using comprehensive spectroscopic techniques (e.g. grazing incidence X-ray diffraction (GIXRD)) and complementary density functional theory (DFT) calculations. Furthermore, the N-doped Ti3C2 quantum dots are applied as an ultra-sensitive heavy iron ion (Fe3+) detector probe with a detection limit of up to 100 μM. Additionally, the as-developed MXene quantum dots have huge prospects in biological sensing by functioning as an appealing mediator-free biosensor for the detection of H2O2 with high sensitivity. Overall, this work will provide a blueprint for the design of 2D-QDs based on MXene toward meeting the continuous upsurge in demand for a plethora of technological applications such as electronics, solar cells, optical, biomedical, and environmental fields.

Facile preparation of high-performance Fe-doped Ce–Mn/TiO2 catalysts for the low-temperature selective catalytic reduction of NOx with NH3

A Ce–Mn–Fe/TiO2 catalyst has been successfully prepared using a single impregnation method, and excellent low-temperature NH3-SCR activity was demonstrated in comparison with other typical SCR catalysts including Mn–Ce/TiO2 and metal-doped Mn–Ce/TiO2. The crystal structure, morphology, textural properties, valence state of the metals, acidity and redox properties of the novel catalyst were investigated comprehensively by X-ray diffraction (XRD), N2 adsorption and desorption analysis, X-ray photoelectron spectroscopy (XPS), NH3-temperature-programmed desorption (NH3-TPD), and H2-temperature-programmed reduction (H2-TPR). The Fe-doped Ce–Mn/TiO2 catalyst boosted the low-temperature NH3-SCR activity effectively under a broad temperature range (100–280 °C) with a superior NO conversion rate at low temperatures (100 °C, 96%; 120–160 °C, ∼100%). Fe doping caused this improvement by enlarging the catalyst pore volume, improving the redox properties, and increasing the amount of acidic sites. These properties enhanced the ability of the catalyst to adsorb NH3 and improved the low-temperature SCR performance, especially at temperatures lower than 150 °C. Moreover, redox cycles of Ce, Mn, and Ti (Mn4+ + Ce3+ ↔ Mn3+ + Ce4+, Mn4+ + Ti3+ ↔ Mn3+ + Ti4+) also played an important role in enhancing the low-temperature SCR efficiency by accelerating the electron transfer. The excellent NH3-SCR result is promising for developing environmentally-friendly and more effective industrial catalysts in the future.

Sulfur resistance of Ce-Mn/TiO 2 catalysts for low-temperature NH 3 –SCR

Ce-Mn/TiO2 catalyst prepared using a simple impregnation method demonstrated a better low-temperature selective catalytic reduction of NO with NH3 (NH3–SCR) activity in comparison with the sol-gel method. The Ce-Mn/TiO2 catalyst loading with 20% Ce had the best low-temperature activity and achieved a NO conversion rate higher than 90% at 140–260°C with a 99.7% NO conversion rate at 180°C. The Ce-Mn/TiO2 catalyst only had a 6% NO conversion rate decrease after 100 ppm of SO2 was added to the stream. When SO2 was removed from the stream, the catalyst was able to recover completely. The crystal structure, morphology, textural properties and valence state of the metals involving the novel catalysts were investigated using X-ray diffraction, N2 adsorption and desorption analysis, X-ray photoelectron spectroscopy, scanning electron microscopy and energy dispersive spectroscopy, respectively. The decrease of NH3–SCR performance in the presence of 100 ppm SO2 was due to the decrease of the surface area, change of the pore structure, the decrease of Ce4+ and Mn4+ concentration and the formation of the sulfur phase chemicals which blocked the active sites and changed the valence status of the elements.

Multicolor carbon nanodots from food waste and their heavy metal ion detection application

Multicolor carbon dots (C-dots) have excellent performance characteristics, high photoluminescence efficiency, ease of fabrication and low toxicity. C-dots have been used in a wide variety of fields including bioimaging, biomedicine, photocatalysis and environmental monitoring. The mass production of multicolor CDs using low-cost, facile methods is an important issue for future industrial applications. In this article, we reported a simple and highly effective way to prepare the multicolor C-dots and use them to detect heavy metal iron ions. Hydrochar acquired from food waste processed with hydrothermal carbonization (HTC) was used as the carbonaceous material for this process. Four colors of C-dots were obtained and included blue, green, yellow and red. These multicolor C-dots could be used as fluorescence probes with unique selectivity to detect the Fe3+ ion. The luminescence response ranged from 1 to 50 μM with a correlation coefficient of 0.9968. This discovery not only shows the high value-added products which can be obtained from food waste but can also lead to new developments in carbonaceous materials which can be used as “green resources”.

Surface Properties of Organic Kerogen in Continental and Marine Shale

The adhesion energy of kerogen in continental and marine shale was innovatively discovered using the colloid probe technique with atomic-force microscopy (AFM). AFM results indicated that the adhesion force of kerogen was higher than the inorganic material in both the continental and marine shale samples. The chemical elements in the two kinds of samples were measured by energy-dispersive X-ray analysis with scanning electron microscopy (SEM). The chemical compositions of kerogen involved C═C bonding, C═O bonding, pyridine nitrogen, and pyrrole nitrogen, whereas the primary constituent involving inorganic matter was Si-O bonding. These results were confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The high percentages of C═C and C═O bonding in kerogen are attributed to the large dipole on the kerogen surface which allowed kerogen to contain liquid and gaseous hydrocarbons.