Effect of varying oxygen concentrations on the shelf-life of fresh pork sausages packaged in modified atmosphere

A total of 105 fresh pork sausages were packaged in atmospheres varying in oxygen concentration, using the following mixtures (%O₂/%CO₂/%N₂): 0/20/80, 0/20/80 + O₂ scavenger, 20/20/60, 40/20/40, 60/20/20, and 80/20/0. In addition, two batches were subjected to vacuum packaging or over-wrap with O₂-permeable film. They were stored for 20 days at 2 ± 1 °C in the dark. Values of pH, CIE L*, a* and b* color parameters, surface metmyoglobin percentage, TBA-reactive substances, psychrotroph aerobe bacterial numbers and sensory discoloration and off-odor were assessed throughout storage. Packaging in the absence of O₂, either under vacuum or in atmosphere with O₂ scavenger, led to extension of shelf-life in terms of both color and odor stability due to low oxidation rates. Increase of O₂ caused a significant enhancement of oxidation, decrease of shelf-life due to discoloration and off-odor development. The highest O₂ concentration gave rise to a significant color improvement, though only for a limited period of 8 days.     

Regeneration of Pd/TiO2 catalyst deactivated in reductive CCl4 transformations by the treatment with supercritical CO2, ozone in supercritical CO2 or oxygen plasma

Carbonaceous deposits formation was established as the primary reason of Pd/TiO₂ catalyst deactivation during reductive processing of CCl₄ to form hydrodechlorination and oligomerization products. Three methods of carbonaceous deposits elimination were tested: (1) extraction by supercritical CO₂, (2) oxidation by ozone in supercritical CO₂, and (3) low-temperature glow-discharge oxygen plasma treatment. Synchronic thermal analysis confirms effective carbonaceous deposits removal during regeneration by ozone or low temperature glow-discharge oxygen plasma; by XPS deep oxidation of surface Pd after oxidative treatment (by ozone or oxygen plasma) was found. Thus H₂ reduction was proposed as the second step making possible full regeneration of initial catalytic activity of Pd/TiO₂.     

Interaction of water with the clean and oxygen pre-covered Ir(1 1 1) surface

Adsorption and reaction of water on the clean and oxygen modified Ir(1 1 1) single crystal surfaces have been studied using temperature programmed desorption (TPD) and molecular beam reactive scattering (MBRS) techniques under ultrahigh vacuum (UHV) conditions. Water dissociates on the clean Ir(1 1 1) surface with a probability (estimated based on production of hydrogen) which decreases from 0.016 to 0.004 ± 0.0015 with increasing water coverages from 0.34 to 2.59 monolayer. Scattering experiments performed at various surface temperatures in the limit of zero coverage yield water dissociation probabilities in the range of 0.0005–0.012 (300–900 K) with an uncertainty expressed as ±20% of the dissociation probability. The apparent activation energy for water dissociation on clean Ir(1 1 1) is estimated to be 170 ± 5 kJ/mol employing MBRS techniques, which probably cannot be applied to TPD measurements with higher water coverages. We speculate that water dissociation occurs on the defects of the Ir(1 1 1) surface. Using isotopically labeled reactants, a strong interaction between adsorbed water and oxygen was found on Ir(1 1 1), indicated by a new water desorption feature at 235 K and scrambled oxygen and water desorption products.     

XPS and UPS in situ study of oxygen thermal desorption from nanocrystalline diamond surface oxidized by different process

The chemistry of oxygen bonding on the diamond surface is a rich area of surface science research. It is well known that different surface terminations lead to strong variation of the material work function. This effect in diamond assumes peculiar consequences. In fact the oxidized diamond surface is hydrophilic, due to the high work function it shows a positive electron affinity and it is non conductive. On the contrary hydrogenation completely changes the orientation of the surface dipoles, the surface becomes hydrophobic, the work function lowers leading to a negative electron affinity. In addition hydrogen induces subsurface carriers which render the diamond surface semiconducting. These distinctive electronic properties make the diamond surface very interesting for the fabrication of surface field effect transistors just playing with the oxygen/hydrogen chemistry. Hydrogenation is generally obtained during the diamond synthesis in plasma reactors. Differently, the diamond surface oxidation may be accomplished with different processes (wet chemistry, plasma, UV irradiation).The realization of electronic devices calls for a complete understanding of the carbon-oxygen interactions, their stability and their influence on the electronic properties of diamond. Aim of this work is to explore the properties of diamond surfaces oxidized with piranha mixture, with O₂ plasma and with UV irradiation in a pure O₂ atmosphere. Each of these oxidized surfaces were annealed in situ at different temperatures and analyzed with photoelectron spectroscopies. Decreases of the oxygen concentration obtained via thermal desorption are then correlated with variations of the electronic properties obtained from UPS analyses.     

水质五日生化需氧量(BOD5)测量不确定度的评定

水质五日生化需氧量测量的关键是用碘量法侧水中溶解氧的含量,经过分析碘量法测定水中溶解氧含量测量不确定度的影响因素,认为测量的重复性的不确定度分量最大,其次是样品中溶液的体积,滴定溶液的体积和滴定溶液的浓度等不确定度分量。计算得到水中五日生化需氧量的侧定结果的合成不确定度为6.5mg/L,扩展不确定度为13.0mg/L。     

Direct measurement of mass transfer around a single bubble by micro-PLIFI

In this paper, an original direct and non-intrusive technique using Planar Laser Induced Florescence with Inhibition (PLIFI) is proposed to quantify the local mass transfer around a single spherical bubble rising in a quiescent liquid. The new set-up tracks the mass transferred in the bubble wake for a plane perpendicular to the bubble trajectory instead of a parallel plane as in previous works, thus avoiding optical reflection problems. A spherical bubble is formed in a glass column containing fluorescent dye. A camera with a microscopic lens is placed underneath the column to record cross-sections of the transferred oxygen. A high-speed camera is located far from the column to simultaneously record the bubble position, size, shape and velocity. The dissolved gas inhibits the fluorescence so that oxygen concentration fields can be measured. From this, a calculation method is developed to determine mass transfer on the micro-scale. Experimental results are compared to the Sherwood numbers calculated from the Frössling and Higbie models used for fully contaminated and clean spherical bubbles, respectively. Results show that all experimental Sherwood numbers occur between the two models, which gives credence to the measurements. The new technique is then developed for bubble diameters ranging from 0.7 to 2 mm in six hydrodynamic conditions (1<Re<10², 10²<Sc<10⁶).     

Nb–TiO2 supported platinum nanocatalyst for oxygen reduction reaction in alkaline solutions

Platinum based nanocatalyst at home made Nb–TiO₂ support was synthesized and characterized as the catalyst for oxygen reduction reaction in 0.1 mol dm⁻³ NaOH, at 25 °C. Nb doped TiO₂ catalyst support, containing 5% of Nb, has been synthesized by modified acid-catalyzed sol–gel procedure in non-aqueous medium. BET and X-ray diffraction (XRD) techniques were applied for characterization of synthesized supporting material. XRD analysis revealed only presence of anatase TiO₂ phase in synthesized support powder. Existence of any peaks belonging to Nb compounds has not been observed, indicating Nb incorporated into the lattice.Nb–TiO₂ supported Pt nanocatalyst synthesized, using borohydride reduction method, was characterized by TEM and HRTEM techniques. Platinum nanoparticles distribution, over Nb doped TiO₂ support, was quite homogenous. Mean particle size of about 4 nm was found with no pronounced particle agglomeration. Electrochemical techniques: cyclic voltammetry and linear sweep voltammetry at rotating disc electrode were applied in order to study kinetics and estimate catalytic activity of this new catalyst for the oxygen reduction reaction in alkaline solution. Two different Tafel slopes were found: one close to −90 mV dec⁻¹ in low current density region and other approximately −200 mV dec⁻¹ in high current density region, which is in good accordance with literature results for oxygen reduction at Pt single crystals, as well as Pt nanocatalysts in alkaline solutions. Similar specific catalytic activity (expressed in term of kinetic current density per real surface area) of Nb(5%)–TiO₂/Pt catalyst for oxygen reduction reaction in comparison with the carbon supported platinum (Vulcan/Pt) nanocatalyst, was found.     

Chemical - Looping with oxygen uncoupling using Mn/Mg-based oxygen carriers - Oxygen release and reactivity with methane

Chemical-looping combustion with oxygen uncoupling (CLOU) is a method for combustion of solid and gaseous fossil fuels, which enables easy separation of carbon dioxide from the gaseous product mixture. In contrast to the related chemical-looping combustion (CLC) technology where gaseous or gasified fuels react directly with oxygen carriers, CLOU processes require oxygen carrier materials to be able to release oxygen in the fuel reactor and to regenerate by re-oxidation in oxygen-rich atmosphere in the air reactor at elevated temperature. Oxygen uncoupling properties and reactivities for methane combustion of 12 oxygen carrier particles, produced from mixtures of manganese and magnesium oxides with optional addition of titanium dioxide or calcium hydroxide, are investigated in a quartz batch reactor at 810 °C, 850 °C, 900 °C and 950 °C. All investigated oxygen carriers have oxygen release characteristics. The addition of calcium hydroxide facilitates oxygen release and combustion of methane, whereas addition of titanium dioxide does not have a pronounced effect on either oxygen uncoupling or reactivity of the oxygen carrier. In general, particles with greater extent of oxygen release have superior methane combustion properties.     

Investigation on properties of a novel ceria-zirconia-praseodymia solid solution and its application in Pd-only three-way catalyst for gasoline engine emission control

Different contents of praseodymia were introduced to modify Ce_0.2Zr_0.8O₂ (CZ) and the supported Pd-only three-way catalysts before and after aging were also prepared. The influence of praseodymia doping on the structural/textural properties of CZ and the effect on the three-way catalytic activity were investigated. Structural and textural characterizations reveal that the addition of praseodymia results in the formation of Ce-Zr-Pr ternary solid solution (CZP) with higher specific surface area, better thermal stability and larger oxygen storage capacity (OSC) than that of CZ. It is more credible that Zr is replaced by Pr during the formation of CZP. The modified Pd-only three-way catalysts present relatively higher catalytic activity to the main target pollutants in gasoline engine exhaust and exhibit wider air/fuel operation window due to the improved properties of CZP.     

Fe-based catalysts for oxygen reduction in proton exchange membrane fuel cells with cyanamide as nitrogen precursor and/or pore-filler

Fe/N/C catalysts for oxygen reduction reaction were synthesized via impregnation or ballmilling. The role of cyanamide (CM) as nitrogen precursor and/or pore-filler for a highly microporous carbon (Black Pearls 2000) was investigated. The use of CM in this work resulted in two main differences compared with phenanthroline from our previous work; (i) ballmilling the precursors did not result in improved activity of the resulting catalysts, and (ii) the activity after the first pyrolysis in argon was relatively high, but did not increase after a second pyrolysis in NH₃. These differences may be explained by TGA measurements of both pore-fillers, where complete gasification of CM is observed at temperatures above 750 °C in Ar, while pyrolysis of phenanthroline in Ar results in 20 wt% residual carbon-based material. Consequently, when using CM as pore-filler with a highly microporous carbon support, the maximum microporous surface area and nitrogen content is reached after only a single pyrolysis in Ar. The most active catalyst prepared with CM was obtained by pyrolysing in Ar at 950 °C a catalyst precursor containing 1 wt% Fe, 80 wt% CM and Black Pearls 2000. This catalyst possessed about 1/6th the catalytic activity of best reported using phenanthroline as a pore-filler. Changing the carbon support had effects on the activity and stability of the catalysts. The catalysts made with a non-porous furnace black (N330) or carbon nanotubes as a carbon support were more stable but less performing than those using carbon supports having high microporous surface area like Black Pearls 2000 or Ketjenblack. The desirable properties for a pore-filler molecule used in the synthesis of Fe/N/C-catalysts by the pore-filling method are discussed.