Sotiris E. Pratsinis

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Pratsinis

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Sotiris E.

ORCID

0000-0003-2042-249X

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Publications 1 - 10 of 49

Trade-off between soot and NO emissions during enclosed spray combustion of jet fuel
Trivanovic, Una; Pratsinis, Sotiris E. (2024)
Scientific Reports
Aviation emissions of soot and nitrogen oxides are strictly regulated as they adversely impact human health and the environment. Jet fuel combustion conditions that decrease one pollutant concentration increase the other. Although it is not impossible to achieve both low soot and NOx through clever design, it is hard to simultaneously reduce both. Although it is difficult to study such conditions due to high temperatures and gas flowrates of aircraft engines, recently it was shown that Enclosed Spray Combustion (ESC) of jet fuel results in soot with similar characteristics to that from aircrafts making ESC an attractive unit for studying aviation-like emissions. Furthermore, judicious swirl-injection of air downstream of the ESC burner drastically reduces soot emissions. Here the trade-off between NO and soot emissions during combustion of jet fuel is studied for the first time, to the best of our knowledge, accounting for the detailed structure of soot. Injecting air shortly after the ESC burner decreases soot but increases NO emissions, while such injection further downstream has the inverse outcome. This interplay between soot and NO emissions was correlated quantitatively with the gas temperature shortly after air injection. Consequently, combustion conditions for an optimal trade-off between soot and NO emissions for the ESC conditions studied here are identified that are at or below the lowest NOx emissions per unit mass of fuel from existing aircraft engines.
The Influence of ZnO-ZrO2 Interface in Hydrogenation of CO2 to CH3OH
Šot, Petr; Noh, Gina; Weber, Ines; et al. (2022)
Helvetica Chimica Acta
The influence of the interface in ZnO-ZrO2 catalysts for the selective hydrogenation of CO2 to CH3OH is investigated. Specifically, we perturbed its structure using two different synthetic methods: surface organometallic chemistry (SOMC) and flame-spray pyrolysis (FSP) and investigated the speciation of the resulting materials by spectroscopic techniques, such as XAS, NMR, IR, UV-Vis, and EPR. The results indicate that oxidic Zn particles that co-exist with ZrO2, as synthesized by FSP, show a superior selectivity in contrast to Zn(0) nanoparticles or Zn(II) single sites on ZrO2, formed using SOMC. Further experiments underlined the importance of the ZnO-ZrO2 interface in the process: only materials with such an interface exhibit highly selective production of CH3OH, proceeding likely via the formation of the surface CH3O intermediates.
Synthesis of Catalytic Materials in Flames: Opportunities and Challenges
Koirala, Rajesh; Pratsinis, Sotiris E.; Baiker, Alfons (2016)
Chemical Society Reviews
The proven capacity of flame aerosol technology for rapid and scalable synthesis of functional nanoparticles makes it ideal for the manufacture of an array of heterogeneous catalysts. Capitalizing on the high temperature environment, rapid cooling and intimate component mixing at either atomic or nano scale, novel catalysts with unique physicochemical properties have been made using flame processes. This tutorial review covers the main features of flame synthesis and illustrates how the physical and chemical properties of as-synthesized solid catalytic materials can be controlled by proper choice of the process parameters. Gas phase particle formation mechanisms and the effect of synthesis conditions (reactor configuration, precursor and dispersion gas flow rates, temperature and concentration fields) on the structural, chemical and catalytic properties of as-prepared materials are discussed. Finally, opportunities and challenges offered by flame synthesis of catalytic materials are addressed.
Coatings, Coated Implants And Manufacturing Methods Therefore
Herrmann, Inge; Matter, Tino; Pratsinis, Sotiris E. (2021)
The present invention relates to novel coatings and its uses, as well as processes of making such coatings. The coatings are characterized by their chemical composition and architecture; they are antimicrobial, tissue regenerative and tissue bonding, making them useful as a coating of an implant. Manufacturing processes for such coating combines flame spray pyrolysis and direct coating of a substrate; the process uses inexpensive starting materials and is scalable.
Population Balance Modeling of Flame Synthesis of Titania Nanoparticles
Tsantilis, Stavros; Kammler, Hendrik K.; Pratsinis, Sotiris E. (2002)
Chemical Engineering Science
The significance of various particle formation pathways during flame synthesis of titania nanoparticles by titanium tetraisopropoxide oxidation in a premixed methane–oxygen flame is investigated by population balance modeling. An efficient moving sectional model is developed accounting for gas phase chemical reactions, coagulation, surface growth and sintering. The model is validated by comparing it against standard sectional solutions and detailed but cumbersome literature models at certain limiting cases (i.e., only coagulation and sintering, only surface growth or only coagulation). The evolution of primary particle size distribution is monitored by rapid thermophoretic sampling and image analysis of transmission electron microscope pictures while the corresponding flame temperature is measured in the presence of particles by Fourier transform infra-red spectroscopy. Excellent agreement is obtained between model predictions and data with respect to the evolution of average primary particle diameter and geometric standard deviation without any adjustable parameters until conditions of pure agglomeration of polydisperse particles are established (here, approximately after the first above the burner tip). By comparing detailed measured and calculated size distributions, surface reaction appears to be the dominant route for early particle growth at the conditions studied.
Influence of remote control in Pt/BaAl2O3 NOx storage-reduction catalysts
Büchel, Robert; Strobel, Reto; Pratsinis, Sotiris E.; et al. (2007)
Chimia
Opinion: Eliminating aircraft soot emissions
Trivanovic, Una; Pratsinis, Sotiris E. (2024)
Aerosol Research
Soot from aircraft engines deteriorates air quality around airports and can contribute to climate change primarily by influencing cloud processes and contrail formation. Simultaneously, aircraft engines emit carbon dioxide (CO2), nitrogen oxides (NOx), and other pollutants which also negatively affect human health and the environment. While urgent action is needed to reduce all pollutants, strategies to reduce one pollutant may increase another, calling for a need to decrease, for example, the uncertainty associated with soot's contribution to net radiative forcing (RF) in order to design targeted policies that minimize the formation and release of all pollutants. Aircraft soot is characterized by rather small median mobility diameters, dm=8–60 nm, and at high thrust, low (< 25 %) organic carbon to total carbon (OC/TC) ratios, while at low thrust, the OC/TC can be quite high (> 75 %). Computational models could aid in the design of new aircraft combustors to reduce emissions, but current models struggle to capture the soot, dm, and volume fraction, fv, measured experimentally. This may partly be due to the oversimplification of soot's irregular morphology in models and a still poor understanding of soot inception. Nonetheless, combustor design can significantly reduce soot emissions through extensive oxidation or lean, near-premixed combustion. For example, lean, premixed prevaporized combustors significantly reduce emissions at high thrust by allowing injected fuel to fully vaporize before ignition, while low temperatures from very lean jet fuel combustion limit the formation of NOx. Alternative fuels can be used alongside improved combustor technologies to reduce soot emissions. However, current policies and low supply promote the blending of alternative fuels at low ratios (∼ 1 %) for all flights, rather than using high ratios (> 30 %) in a few flights which could meaningfully reduce soot emissions. Here, existing technologies for reducing such emissions through combustor and fuel design will be reviewed to identify strategies that eliminate them.
Luminescence and crystallinity of flame-made Y2O3:Eu3+ nanoparticles
Camenzind, Adrian; Strobel, Reto; Krumeich, Frank; et al. (2007)
Advanced Powder Technology
Cubic and/or monoclinic Y2O3:Eu3+ nanoparticles (10–50 nm) were made continuously without post-processing by single-step, flame spray pyrolysis (FSP). These particles were characterized by X-ray diffraction, nitrogen adsorption and transmission electron microscopy. Photoluminescence (PL) emission and time-resolved PL intensity decay were measured from these powders. The influence of particle size on PL was examined by annealing (at 700–1300°C for 10 h) as-prepared, initially monoclinic Y2O3:Eu3+ nanoparticles resulting in larger 0.025–1 μm, cubic Y2O3:Eu3+. The influence of europium (Eu3+) content (1–10 wt%) on sintering dynamics as well as optical properties of the resulting powders was investigated. Longer high-temperature particle residence time during FSP resulted in cubic nanoparticles with lower maximum PL intensity than measured by commercial micron-sized bulk Y2O3:Eu3+ phosphor powder. After annealing as-prepared 5 wt% Eu-doped Y2O3 particles at 900, 1100 and 1300°C for 10 h, the PL intensity increased as particle size increased and finally (at 1300°C) showed similar PL intensity as that of commercially available, bulk Y2O3:Eu3+ (5 μm particle size). Eu doping stabilized the monoclinic Y2O3 and shifted the monoclinic to cubic transition towards higher temperatures.
Toward Elimination of Soot Emissions from Jet Fuel Combustion
Kelesidis, Georgios A.; Nagarkar, Amogh; Trivanovic, Una; et al. (2023)
Environmental Science & Technology
Soot from jet fuel combustion in aircraft engines contributes to global warming through the formation of contrail cirrus clouds that make up to 56% of the total radiative forcing from aviation. Here, the elimination of such emissions is explored through N2 injection (containing 0−25 vol % O2) at the exhaust of enclosed spray combustion of jet fuel that nicely emulates aircraft soot emissions. It is shown that injecting N2 containing 5 vol % of O2 enhances the formation of polyaromatic hydrocarbons (PAHs) that adsorb on the surface of soot. This increases soot number density and volume fraction by 25 and 80%, respectively. However, further increasing the O2 concentration to 20 or 25 vol % enhances oxidation and nearly eliminates soot emissions from jet fuel spray combustion, reducing the soot number density and volume fraction by 87.3 or 95.4 and 98.3 or 99.6%, respectively. So, a judicious injection of air just after the aircraft engine exhaust can drastically reduce soot emissions and halve the radiative forcing due to aviation, as shown by soot mobility, X-ray diffraction, Raman spectroscopy, nitrogen adsorption, microscopy, and thermogravimetric analysis (for the organic to total carbon ratio) measurements.
Embedding Pd into SnO₂ drastically enhances gas sensing
Jablczynska, Katarzyna; Gogos, Alexander; Kubsch, Christian M.P.; et al. (2024)
Nanoscale Advances
Combustion aerosol processes can uniquely embed noble metals into semiconducting particles. Here, monocrystalline SnO2 particles embedded with Pd and/or PdOx were made by flame spray pyrolysis (FSP) of appropriate precursors through microexplosions by droplet-to-particle conversion as the crystal size was proportional to the cube root of precursor solution concentration, C. These particles were air-annealed and leached with nitric acid for removal of metallic Pd from their surface. The SnO2 crystal size varied from 11 to 24 nm and was in close agreement with the primary particle size determined by nitrogen adsorption. The embedded fraction of Pd ranged from about 30 to 80% of the nominal Pd-content. This was achieved by judiciously varying the C, Pd content and the ratio of precursor solution to dispersion oxygen flowrates during FSP. The response of sensors made by doctor blading films of such particles to 1 ppm of acetone and CO was evaluated at 350 degrees C and 50% relative humidity. Embedding Pd/PdOx into SnO2 significantly increased the sensor response: 2-6 times over that of pure or conventionally-made Pd-containing SnO2 sensors at low nominal Pd-contents (0.2 mol%). For higher ones (i.e. 1 mol% Pd), the sensor response was enhanced by up to two orders of magnitude. This is attributed to Pd atoms in the SnO2 lattice near the particle surface and/or Pd/PdOx clusters acting as nanoelectrodes into SnO2 films and altering their transducing properties as shown by high resolution electron microscopy, XPS and baseline resistance measurements of pure and Pd-embedded SnO2 sensing films.

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