Oxygen Partial Pressure Range Research Articles

Experimental Investigation of Gas/Matte/Spinel Equilibria in the Cu-Fe-O-S System at 1473 K (1200 °C) and P(SO2) = 0.25 atm

The Cu-Fe-O-S system is the key system for the characterisation of the phase chemistry in high-temperature copper making processes. An experimental study was undertaken to investigate the gas/matte/spinel equilibria in the Cu-Fe-O-S system at 1473 K (1200 A degrees C), P(SO2) = 0.25 atm, and a range of oxygen partial pressures. The experimental methodology involved high temperature equilibration using a primary phase substrate technique in controlled gas atmospheres (CO/CO2/SO2/Ar), rapid quenching of the equilibrated phases, followed by direct measurement of phase compositions using electron probe x-ray microanalysis. Particular attention was given to the analysis of reactions during equilibration and confirmation of the achievement of equilibrium in the present study. The new data provide important information for understanding of the gas/matte/spinel interactions at high temperature and provide an essential foundation for the development of the multicomponent thermodynamic database for copper-containing systems.

Evolution and Preliminary Testing of a Hyperoxic Therapy for Autism Spectrum Disorders

The diagnosis of autism spectrum disorders (ASD) comprises a range of developmental disabilities, the established prevalence of which has been increasing globally. Despite decades of research, however, ASD is still not well understood and a generally accepted intervention or group of interventions which consistently and comprehensively address the spectrum of needs has not yet been identified or developed. Thus, in seeking a solution to their children's conditions, some parents have felt compelled to try complementary and alternative medical treatments.One such intervention that has attracted some advocates is off-label hyperbaric oxygen therapy. In examining the data for this application, we were struck by the wide range of oxygen partial pressures reported to have benefit and the fact that many could be easily provided at normobaric pressure. As we knew of no reason for the use of increased pressure in treating ASD with hyperoxic therapy, we determined to find out if benefits could be obtained from such treatments at normal atmospheric pressure.A pilot study with five cases involving preteens and teenagers with autism was conducted using a normobaric form of hyperoxic treatment we have called Microbaric® Oxygen Therapy (MBO2). All five cases benefitted, three remarkably so. Improvements were across the full range of symptoms of autism, and no regression was reported on cessation of treatment or during follow up for as long as six years. Thus, it appears that the outcomes of MBO2 for autism are permanent. As a consequence of this pilot study, it would seem imperative to conduct controlled research to confirm our findings. Should similar outcomes be obtained, then MBO2 would offer a new, cost-effective, and time efficient way forward as a stand-alone therapy or as an adjunct to other therapies in the treatment of autism.

Oxygen Content and Thermodynamic Stability of YBaCo2O6−δ Double Perovskite

The thermodynamic stability of the double perovskite YBaCo2O6−δ was studied using the coulometric titration technique and verified by measurements of the overall conductivity depending on oxygen partial pressure at a given temperature. As a result, the stability diagram of YBaCo2O6−δ was plotted. YBaCo2O6−δ was found to be thermodynamically stable in air at 850°C and higher temperatures, whereas its thermodynamic stability at 900°C is limited by the range of oxygen partial pressures −3.56 ≤ log(pO2/atm) ≤ −0.14. Oxygen content in YBaCo2O6−δ slightly decreases at 900°C from 5.035 at log(pO2/atm) = −0.14 to 4.989 in the atmosphere with log(pO2/atm) = −3.565 indicating a crucial role which variation of Co+3/Co+2 ratio plays in its stability. YBaCo2O6−δ decomposes into the mixture of YCoO3 and BaCoO3−z at the high pO2 stability limit, whereas YBaCo4O7, BaCo1−xYxO3−γ, and Y2O3 were identified as the products of its decomposition at the low pO2 one.

On the defect chemistry of BaFe0.89Al0.01Ta0.1O3‐δ, a material for temperature independent resistive and thermoelectric oxygen sensors

The Seebeck-coefficient (aka thermopower) is a less wide-spread parameter to determine constants for defect chemical models of semiconductor oxides. It is a measure for the charge carrier concentration. In contrast to the often investigated electrical conductivity, it has the benefit of being independent of the material geometry. BaFe0.7Ta0.3O3‐δ is known as a temperature-independent conductometric oxygen sensor material with perovskite crystal structure. The present work considers the Seebeck-coefficient as well as the electrical conductivity of bulk and thick-film BaFe0.89Al0.01Ta0.1O3‐ δ (BFAT10). Seebeck-coefficient and electrical conductivity were measured simultaneously between 600 and 950°C under varying oxygen partial pressures from 10−24 to 1bar. BFAT10 thick films have been successfully deposited by the novel Aerosol Deposition Method (ADM) at room temperature on a special transducer. The electrical conductivity of thick-film sensors shows almost no temperature dependency but depends strongly on the oxygen partial pressure in the temperature range from 600 to 800°C. An n-to-p-type transition was observed in the investigated oxygen partial pressure and temperature range. The defect parameters were derived from the experimental results and an initial defect model for BFAT10 is discussed. A hopping-type conduction mechanism is assumed due to the very low charge carrier mobility.

Viscosity model for oxide melts relevant to fuel slags. Part 3: The iron oxide containing low order systems in the system SiO2–Al2O3–CaO–MgO–Na2O–K2O–FeO–Fe2O3

The viscosity model recently developed for the fully liquid system SiO2–Al2O3–CaO–MgO–Na2O–K2O is further extended to describe the viscosity of the iron oxide containing low order systems in the Newtonian range. The different structural roles of Fe2+ and Fe3+ to the viscosity are captured by the associate species. Using the monomeric associate species in combination with some specific larger structrual units, the model is capable of describing the viscosity of the melts FeO, FeO–SiO2, FeO–Al2O3, Fe2O3–CaO, Fe2O3–MgO, Fe2O3–Na2O, and Fe2O3–K2O over the whole range of compositions as well as a wide range of temperatures and oxygen partial pressures using only one set of model parameters. A new mechanism is proposed to describe the local viscosity maximum around the fayalite composition in the FeO–SiO2 melt. The model shows that the presence of the local viscosity maximum is dependent on the temperature and oxygen partial pressure. Moreover, the viscosity maximum caused by Al3+- or Fe3+-induced charge compensation is presented and a good agreement between the calculated viscosities and experimental data is demonstrated.

Structural features and high-temperature transport in SrFe0.7Mo0.3O3−δ

The complex oxide SrFe0.7Mo0.3O3−δ was obtained by combustion of the organometallic precursor in air followed by annealing in an argon flow at 1350°C, and characterized with the help of X-ray and electron diffraction methods. Oxygen nonstoichiometry and electrical conductivity data were collected in the oxygen partial pressure range from 10–19 to 0.5atm at temperatures 750–950°C. The as-prepared single phase oxide SrFe0.7Mo0.3O3−δ with the cubic double perovskite structure (SG Fm3m) is shown to undergo a structural transition to the tetragonal double perovskite phase (SG I4mmm) in the result of reducing treatment at pO2 = 10−12atm and 950°C. The ordered phases are characterized by a strong anti-site disordering of iron and molybdenum and nearly zero long-range ordering parameter. The maximal concentration of n-type carriers is about four times larger than of p-type carriers in the studied limits of oxygen pressure and temperature. The mobility of p-type carriers is found to vary within ~ 0.02–0.03cm2V−1s−1 with the migration energy of about 0.4eV, while the n-type mobility being approximately twice higher does not practically depend on temperature. Such features as good electrical conductivity, which can rise up to 40Scm−1 in reducing conditions and a considerable amount of oxygen vacancies favorable for fast oxygen ion transport are beneficial for application of SrFe0.7Mo0.3O3−δ as anode material in SOFCs and oxygen membrane for hydrogen generation by a water splitting.

Defect formation, ordering, and transport in SrFe1–x Si x O3–δ (x = 0.05–0.20)

Oxygen nonstoichiometry of perovskite-like SrFe1–x Si x O3–δ (x = 0.05–0.20), studied by thermogravimetric analysis and coulometric titration in the oxygen partial pressure range 10−20–0.5 atm at 700–950 °C, decreases with Si4+ additions. The equilibrium $$ {p}_{{\mathrm{O}}_2} $$ –T−δ diagrams can be adequately described by a model accounting for anion site-exclusion effects near highly stable SiO4 tetrahedra and energetic favorability of the defect clusters formed by two tetrahedra sharing one oxygen vacancy. This model was validated by atomistic computer simulations. The standard thermodynamic functions for oxygen incorporation and iron disproportionation reactions are essentially independent of silicon concentration, as for the migration activation energies of the p- and n-type electronic charge carriers. On the contrary, at low temperatures, Si-doping leads to a higher oxygen deficiency, simultaneously suppressing long-range vacancy ordering and increasing oxygen coordination of iron cations as estimated from the Mossbauer spectra. These phenomena are associated, again, with vacancy trapping near randomly distributed Si4+. The Mossbauer spectroscopy, transmission electron microscopy, and electron diffraction studies showed that Si4+ substitution progressively reduces the content of brownmillerite-like nanodomains typical for SrFeO3-based materials.

Fabrication of nanoscale yttria stabilized zirconia for solid oxide fuel cell

Yttria stabilized zirconia (YSZ) is the most widespread electrolyte material for solid oxide fuel cell (SOFC) due to its high ionic conductivity and electronic resistivity over a wide range of oxygen partial pressures. In addition, it is chemically stable at high temperature in oxidizing and reducing atmospheres and chemically and mechanically compatible with the other cell components and gas tight. The objective of this paper is to review current status and related researches about the development of nanoscale YSZ used as electrolyte in SOFC from the viewpoint of materials nanostructure and performance associated with the fabrication and optimization processes. The latest development and achievement in nanoscale YSZ materials are presented. Challenges and research trends based on the fundamental understanding of the materials science and engineering for the nanoscale YSZ development for the commercially viable SOFC technologies are discussed.

Mechanical Properties of SOFC Anode Support Materials at Operating Conditions

The mechanical properties of solid-oxide fuel cells (SOFCs) and the materials they are fabricated from play an important role in manufacturability, durability and lifetime of the devices. Functioning cells must maintain a gas-tight seal though the cell, with no cracks or pores from anode or cathode, through a range of temperatures and oxygen partial pressures. The cell must be able to withstand intrinsic stresses in addition to those introduced by the stacking and sealing of the cells. It is known that the environmental conditions can affect the mechanical properties of materials. It has been shown that point defect concentration and temperature change the elastic modulus and strength of fluorite-structured oxides, but these tests were done using quenched samples or at high temperature in air, not at operating conditions. In this work the flexural modulus and strength of SOFC support materials are investigated under varying oxygen partial pressures at elevated temperatures, under the same conditions SOFCs experience during operation. This is achieved by using a three-point bend fixture on a universal testing machine, with a chamber and furnace to control the environmental conditions. From this information, relationships are built relating materials’ modulus and strength to the defect concentrations and temperatures that it would experience during operation.

Stabilization of polar Mn3O4(001) film on Ag(001): Interplay between kinetic and structural stability

Stabilization processes of polar surfaces are often very complex and interesting. Understanding of these processes is crucial as it ultimately determines the properties of the film. Here, by the combined study of Low Energy Electron Diffraction (LEED), X-ray Photoelectron Spectroscopy (XPS) and Ultraviolet Photoemission Spectroscopy (UPS) techniques we show that, although there can be many processes involved in the stabilization of the polar surfaces, in case of Mn3O4(001)/Ag(001), it goes through different reconstructions of the Mn2O4 terminated surface which is in good agreements with the theoretical predictions. The complex surface phase diagram has been probed by LEED as a function of film thickness, oxygen partial pressure and substrate temperature during growth, while their chemical compositions have been probed by XPS. Below a critical film thickness of ∼ 1 unit cell height (8 sublayers or 3 ML) of Mn3O4 and oxygen partial pressure range of 2 × 10−8 mbar < P(O2) ≤ 5 × 10−7 mbar, different surface structures are detected and beyond this thickness a constant evolution of apparent p(2 × 2) structure have been observed due to the coexistence of p(2 × 1) and c(2 × 2) structures. Similar apparent p(2 × 2) structure has also observed by the oxidation of Ag(001)-supported MnO(001) surface. Our study also shows that the substrate temperature during growth plays a crucial role in determining the final structure of the polar Mn3O4 film and as a consequence of that a strong interplay between structural and kinetic stability in the Mn3O4 film has been observed. Further, stripe-like LEED pattern has been observed from the Mn3O4(001) surface, for the film grown at higher oxygen partial pressure (> 5 × 10−7 mbar) and higher temperature UHV annealing. The origin of these stripes has been explained with the help of UPS results.

Thermoablative resistance of ZrB2-SiC-WC ceramics at 2400 °C

Although ZrB2-SiC ceramics have been extensively researched for applications at ultra-high temperatures (>2000 °C), it is well known that at these temperatures the SiC oxidises actively yielding a gaseous sub-oxide, SiO, rather than the protective, passive oxide product, SiO2. This limits the high-temperature range of SiC-bearing ceramics for ultra-high temperature applications. In the present work, the addition of 5 vol% WC has been shown to partially eliminate the active oxidation of SiC in ZrB2-SiC ceramics, even when exposed to an oxyacetylene flame at 2400 °C. In contrast to the porous and fragmentary surface observed with ZrB2-SiC ceramics tested under the same conditions, a dense oxide surface layer was observed that is believed to have resulted in decreasing pO2 in the layers beneath. This had the effect of changing the chemistry of the system and hence the composition of the phases produced. Clear evidence of the presence of SiO2 was observed, thus indicating that the oxidation of the SiC had been partially passive rather than active. A full volatility diagram for WB at 2400 °C was derived, and existing volatility diagrams for ZrB2 and SiC were extended to the same temperature, in order to develop a theoretical understanding of the ablation mechanism. The significantly improved ablation resistance of ZrB2-SiC-WC is consequently mainly attributed to a competitor transition from tungsten boride (WB) to metallic tungsten in the oxygen partial pressure range 10−8 Pa to 10−3 Pa, which retards the occurrence of the active oxidation of the SiC phase.

The effect of the oxygen ratio control of DC reactive magnetron sputtering on as-deposited non stoichiometric NiO thin films

Non-stoichiometric Ni1-xO thin films were prepared on glass substrate by direct current reactive magnetron sputtering in a large range of oxygen partial pressure (0≤pO2≤1Pa). The dependence of the deposited film structure and properties on oxygen stoichiometry were systematically analyzed by X-ray diffraction, X-ray reflectivity, X-ray photoemission spectroscopy, Raman spectroscopy, atomic force microscopy, UV–vis measurements and electrical transport properties measurements. The deposition rates, surface morphology and opto-electrical properties are very sensitive to the oxygen partial pressure lower than 0.05Pa due to the presence of metallic nickel cluster phase determined by X-ray diffraction, X-ray reflectivity and XPS spectroscopy. Presence of nanocrystallized NiO phase was highlighted even for pO2=0Pa. For pO2>0.05Pa, only the NiO phase was detected. Progressive appearance of Ni3+ species is characterized by a fine increase of the lattice parameter and (111) preferred orientation determined by grazing angle X-ray diffraction, fine increase of the X-ray reflectivity critical angle, displacement of the Ni 2p3/2 signal towards lower energy, significant increase of the electrical conductivity and decrease of the total transmittance. Quantification of Ni3+ by XPS method is discussed. We also showed that the use of Raman spectroscopy was relevant for demonstrating the presence of Ni3+ in the Ni1-xO thin films.

Oxygen isotope exchange, water uptake and electrical conductivity of Ca-doped lanthanum zirconate

Proton concentration of La1.9Ca0.1Zr2O7−α in H2O–O2 atmospheres has been measured by means of the method of high temperature thermogravimetry. The oxygen diffusion coefficient and the oxygen surface exchange coefficient have been measured for La1.9Ca0.1Zr2O7−α over the temperature range of 600–900°C using the oxygen isotope exchange method with gas phase equilibration. pO2-dependencies of the electrical conductivity have been determined in the temperature range 500–800°C and oxygen partial pressure range of 10−20<pO2<0.21atm in atmosphere saturated with water vapour at 25 °С (pН2О=0.03atm). Ionic conductivity has been divided into protonic and oxygen-ionic components. The influence of oxygen defect structure on the water uptake, oxygen diffusivity and electrical conductivity of La1.9Ca0.1Zr2O7−α has been discussed.

A defect model for UO2+x based on electrical conductivity and deviation from stoichiometry measurements

Electrical conductivity of UO2+x shows a strong dependence upon oxygen partial pressure and temperature which may be interpreted in terms of prevailing point defects. A simulation of this property along with deviation from stoichiometry is carried out based on a model that takes into account the presence of impurities, oxygen interstitials, oxygen vacancies, holes, electrons and clusters of oxygen atoms. The equilibrium constants for each defect reaction are determined to reproduce the experimental data. An estimate of defect concentrations and their dependence upon oxygen partial pressure can then be determined. The simulations carried out for 8 different temperatures (973–1673 K) over a wide range of oxygen partial pressures are discussed and resulting defect equilibrium constants are plotted in an Arrhenius diagram. This provides an estimate of defect formation energies which may further be compared to other experimental data or ab-initio and empirical potential calculations.

Tunable, Endotaxial Inclusion of Crystalline Pt-Based Nanoparticles Inside a High-Quality Bronze TiO2 Matrix

A series of high-quality bronze titanium oxide films containing endotaxially embedded Pt-based nanoparticles was fabricated using pulsed laser deposition under various oxygen partial pressures (0 to 50 mTorr). We found that morphological control over the embedded Pt nanoparticles is possible by varying the oxygen partial pressure during growth. We also found that the titanium oxide matrix plays an important role in controlling composition, shape, and distribution of the endotaxially embedded Pt-based nanoparticles over this range of oxygen partial pressure by affecting (1) the formation of a segregated layer of Pt–Ti alloy nanoparticles, in addition to the pure Pt nanoparticles, under vacuum, (2) the generation of crystallographic twinning, steps, and kinks within the Pt nanoparticles, and (3) the localized precipitation of Pt nanoparticles spatially confined and morphologically adapted to the extended defects within the matrix.

Development of electrochemically active electrodes for BaCe0.89Gd0.1Cu0.01O3 − δ proton conducting electrolyte

A row of Co-free and Co-containing electrode materials were synthesized and characterized and the electrode polarization resistance in contact with a proton-conducting BaCe0.89Gd0.1Cu0.01O3−δ electrolyte was studied by means of electrochemical impedance spectroscopy in a temperature range of 600–800°C, an oxygen partial pressure range of 10−3–0.21atm and a water partial pressure range of 4×10−4–0.1atm. The electrodes with Pr1.9Ca0.1NiO4+δ–BaCe0.89Gd0.1Cu0.01O3−δ and Y0.8Ca0.2BaCo4O7+δ functional layers was found to exhibit the lowest polarization resistance equal to 0.49 and 0.46Ωcm2 at 700°C, respectively, with less pronounced deterioration of their characteristics in wet conditions than for all the other investigated electrodes. The shunt effect of the electronic conductivity in the electrolyte on the electrode response was shown to be an important factor for consideration when comparing behavior of the electrodes in contact with different proton-conducting electrolytes.

温度1573 Kおよび酸素分圧10&lt;sup&gt;−6&lt;/sup&gt;~10&lt;sup&gt;−2&lt;/sup&gt; atmにおけるFeO&lt;sub&gt;x&lt;/sub&gt;-CaO-SiO&lt;sub&gt;2&lt;/sub&gt;-Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;系のFeO&lt;sub&gt;x&lt;/sub&gt;側液相線

The performance of iron ore sinter in a blast furnace such as strength and reducibility is strongly affected by the amount and the chemical composition of liquid phase in sinter during the sintering process. Thus, it is necessary to control the production of liquid phase during the sintering process. Iron ore sintering process consists of rapid heating of pulverized raw materials, partial reduction reaction of iron ores as well as liquid phase production, which are caused by combustion of cokes and suction of flaming gas. The heating time of raw materials is too short that the chemical reactions within the sinter never reach the thermodynamic equilibriums. Nevertheless, controlling the melt production could be attempted based on the thermodynamic data such as the phase diagrams. In this study, liquidus lines coexisting with iron oxides and/or 2CaO·SiO2 in the FeOx-CaO-SiO2 system have been measured at 1573 K in the range of oxygen partial pressures between 10–6 atm and 10–2 atm. In addition, the effect of Al2O3 content on the liquidus has also been investigated as Al2O3 is a major gangue component affecting the quality of sinter. It has been found that the homogenous liquid region extends over a wide range of CaO/SiO2 (C/S) ratio between 0.6 and 2 or even more for all the measurement oxygen partial pressures. It has also been found that the FeOx content in liquid phase at C/S=1.0 in equilibrium with solid FeOx is almost constant to be 40-45 mass% irrespective of oxygen partial pressures. However, the FeOx content decreases with an increase in Al2O3 content, indicating that the homogenous liquid region in the FeOx-rich side becomes narrower. As a consequence, it is considered that the amount of slag melt produced in sinter during the sintering process becomes smaller with increasing Al2O3 content.

UV absorption and fluorescence properties of gas-phase p-difluorobenzene

1,4-Difluorobenzene (p-DFB) is a promising aromatic tracer for determining concentration, temperature, and O2 partial pressure in mixing gas flows based on laser-induced fluorescence (LIF). Signal quantification requires the knowledge of absorption and fluorescence properties as a function of environmental conditions. We report absorption and fluorescence spectra as well as fluorescence lifetimes of p-DFB in the temperature, pressure, and oxygen partial pressure range that is relevant for many applications including internal combustion engines. The UV absorption cross section, investigated between 296 and 675 K, has a peak value close to 266 nm and decreases with temperature, while still exceeding other single-ring aromatics. Time-resolved fluorescence spectra were recorded after picosecond laser excitation at 266 nm as a function of temperature (296–1180 K), pressure (1–10 bar), and O2 partial pressure (0–210 mbar) using a streak camera (temporal resolution 50 ps) coupled to a spectrometer. The fluorescence spectra red-shift (~2 nm/100 K) and broaden (increase in full width at half maximum by 58% in the investigated temperature range) with temperature. In N2 as bath gas (1 bar), the fluorescence lifetime τ eff decreases with temperature by a factor of about 20 (from 7 ns at 298 K down to 0.32 ns at 1180 K), while at 8 bar the shortest lifetime at 975 K is 0.4 ns. A noticeable pressure dependence (i.e., reduced τ eff) is only visible at 675 K and above. Quenching of p-DFB LIF by O2 (for partial pressures up to 210 mbar) shortens the fluorescence lifetime significantly at room temperature (by a factor of 8), but much less at higher temperatures (by a factor of 1.8 at 970 K). For fixed O2 partial pressures (52 mbar and above), τ eff shows a plateau region with temperature which shifts toward higher temperatures at the higher O2 partial pressures. O2 quenching is less prominent for p-DFB compared to other aromatic compounds investigated so far. The temperature dependence of O2 quenching can be approximately expressed by an exponential function. The influence of temperature, total pressure, and O2 partial pressure on absorption cross sections and fluorescence quantum yields are given as empirical functions that allow for interpolation. For typical applications, p-DFB LIF provides up to three orders of magnitude stronger signal compared to toluene LIF.

Thermodynamics of Palladium (Pd) and Tantalum (Ta) Relevant to Secondary Copper Smelting

The slag-to-metal distribution ratios of palladium (Pd), $$ L_{\text{Pd}}^{s/m} $$ , in the range of oxygen partial pressure (pO2) from 10−10 to 10−7 atm at 1473 K to 1623 K (1200 °C to 1350 °C); distribution ratios of tantalum (Ta), $$ L_{\text{Ta}}^{s/m} $$ , in the range of pO2 from 10−16 to 10−12 atm at 1673 K and 1873 K (1400 °C and 1600 °C), have been determined in this study. The $$ L_{\text{Pd}}^{s/m} $$ in FeO x -CaO-SiO2-MgO and copper at 1573 K (1300 °C) and pO2 = 10−8 atm is dependant strongly on basicity of slag, i.e. (CaO + MgO)/SiO2 or optical basicity. The current results suggest that Pd presents in the FeO x -CaO-SiO2-MgO slag predominantly as Pd2+. The activity coefficient of PdO in the slag at 1573 K (1300 °C) and pO2 = 10−8 atm was calculated to be in the range of 3.89 × 10−3 to 2.63 × 10−2. The $$ L_{\text{Pd}}^{s/m} $$ was also found to increase with increasing of pO2 and with decreasing of temperature. It was observed that Ta mostly partition to slag phase and very small amount of Ta was found in liquid copper at the high temperature and reduced condition studied. It can be suggested that to promote recovery of palladium from Pd-containing e-waste, a slag with lower silica content and basic flux based, high temperature with reducing atmosphere, is highly desired particularly in secondary copper smelting.

Electrical Conductivity and Defect Equilibria of MoO3-d, a Catalyst for Biofuel Upgrading

The transportation sector currently relies heavily on non-renewable fossil-based fuels to meet its energy requirements. Alternative energy sources need to be developed to meet the projected energy demand in the future in a sustainable and environmentally conscious manner. Bio-oils, generated via biomass fast pyrolysis, represent an attractive avenue for the production of renewable fuels and chemicals. We are investigating MoO3-δ, a promising catalyst for bio-oil upgrading, that selectively transforms various phenolic compounds into aromatic hydrocarbons with high yields using low H2 pressures by hydrodeoxygenation (HDO). While it is widely suggested that both ionic (oxygen vacancies) and electronic defects (e.g. Mo5+/3+), in both the oxide catalyst and oxide support (e.g. TiO2, ZrO2 and Al2O3), play controlling roles in the catalytic reactions, surprising little is known about how operating conditions (temperature, dopants/impurities, and atmosphere (pO2, pH2O, pH2, carbon activity, etc.)) impact the concentration or the diffusivities of these key defects, nor how they influence the reaction kinetics. In this presentation, we discuss our efforts to combine catalysis with defect chemical and impedance spectroscopic approaches to achieving a deeper understanding of the role that defects in metal oxide catalysts and supports play in influencing catalytic selectivity, efficiency, stability and reaction rates. The relationship between the defect equilibria and electrical conductivity is reported for a range of oxygen partial pressures (10-5 - 1 atm O2) and temperatures (300 – 600 oC). Relevant energetics of defect formation and transport are extracted, and their relationships to relevant catalysis processes are discussed.