Trace Amounts Of Impurities Research Articles

Poisoning of automotive methane oxidation catalysts by silicon compounds

Biomethane production offers a viable option to meet the growing demands of renewable energy sources in the transportation sector. However, biomethane contains trace amounts of impurities, such as siloxanes, that can potentially hinder the methane oxidation catalyst performance and lead to excessive greenhouse gas emissions. To investigate this potential problem, the commercial methane oxidation catalysts were poisoned in a laboratory setup with two common siloxanes found in biomethane and with their combustion product, silica. The performances of the clean and poisoned methane oxidation catalysts were measured under realistic lean-burn conditions, after which the catalyst structural changes were determined using XRD, BET and CO chemisorption. The results revealed two different possible poisoning mechanisms. First, both tested siloxanes poisoned the catalysts by migrating selectively on top of the active metal sites and became combusted to form amorphous silica. This caused the methane oxidation performance to drop rapidly with relatively small amounts of siloxane used. In contrast, a significantly higher dose of silica was required to produce a similar poisoning effect because its poisoning mechanism is based on nonselective deposition and physical blocking of the catalyst surface.

Adsorption/Desorption Behaviors of Sulfur Species at Pt Single Crystal Surfaces

Platinum is an excellent electrocatalyst for polymer electrolyte membrane (PEM) fuel cells because it drives hydrogen oxidation and oxygen reduction with very high efficiency. However, when sulfur species contained as a trace amount of impurity in hydrogen fuel and/or pollutant in air adsorb on platinum surfaces, power output significantly decrease because of reduced electrochemically active surface area. Such negative effect caused by the adsorption of sulfur species, so-called sulfur poisoning, is a serious problem because interaction between sulfur species and platinum surfaces is very strong. Thus, understanding and control of adsorption behavior of sulfur species at platinum surfaces are very important to maintain the cell performance of PEM fuel cells. In the present study, adsorption/desorption behaviors of sulfur species at well-defined platinum single crystal surfaces in acidic aqueous solutions are studied by electrochemical measurements, x-ray photoelectron spectroscopy (XPS), and surface x-ray diffraction (SXRD).Prior to each experiment, platinum single crystal surfaces were annealed by induction heating method [1, 2, 3] at 1600°C more than 1 h under the flowing of Ar and H2 mixed gas, followed by cooling under the Ar and H2 flow for 7 min. The surface was immersed in a 1 mM Na2S aqueous solution saturated with Ar and H2 mixed gas, for 1 h. After rinsing with ultrapure water, electrochemical measurements were carried out in an aqueous solution of 0.1 M HClO4 or H2SO4 deaerated with pure N2 gas.At the bare Pt(111) surface, characteristic current responses such as adsorption/desorption of hydrogen and hydroxyl group were observed. After immersing in the sulfur-containing solution, however, those characteristic current responses disappeared, confirming the adsorption of sulfur species and decrease of electrochemically active surface area. XPS in the S 2p region of the Pt(111) surface immersed in the sulfur-containing solution showed three major adsorbed species; adsorbed hydrosulfide ion (Pt-HS- ad) at 161.8 eV, adsorbed sulfur (Pt-Sad) at162.7 eV, and adsorbed polysulfide (Pt-Sn) at 164.3 eV. While Pt-HS- ad reductively desorbed from the surface by the potential sweeping up to -0.2 V vs. Ag/AgCl, Pt-Sad and Pt-Sn oxidatively desorbed by the potential sweeping up to the potential more positive than 0.7 V vs. Ag/AgCl. SXRD showed that the sulfur species adsorbed at the Pt(111) surface in the (√3×√3)R30° structure.At the Pt(100) surface, the oxidative desorption of sulfur species occurred at more positive potential than that at the Pt(111) surface. This indicates that the recovery from sulfur poisoning at the Pt(100) surface is more difficult than that at the Pt(111) surface. Unlike the Pt(111)-(√3×√3)R30° structure, SXRD showed that the sulfur species adsorbed at the Pt(100) surface in the (√2×√2)R45° structure. While the sulfur species occupies a three-fold hollow site of the Pt(111)-(√3×√3)R30° structure, it occupies a four-fold hollow site of the Pt(100)-(√2×√2)R45° structure. The different coordination number of adsorbed sulfur species is considered as the origin of different oxidative desorption behaviors.

False positives from impurities result in incorrect functional characterization of receptors in chemosensory studies

The discovery of chemoreceptors and technological advances have greatly increased our understanding of chemosensory mechanisms. However, some of this rapid progress may have been severely compromised by insufficient attention given to the possible effects of impurities in the chemical standards used in identifying ligands for target receptors. Here, we show that even trace amounts of impurities in test stimuli can completely obscure true ligand-receptor relationships. Responses to impurities may go unrecognized because of two main factors. First, the sensitivity of receptors to ligands may be greater than that of the instruments used to check sample purity. Second, the concentrations of impurities actually reaching the chemoreceptor during experiments may be orders of magnitude higher than that of the putative stimulus, due to large differences in vapour pressure between the impurities and the putative stimulus. Errors caused by impurities are not limited to receptor-ligand studies, but can also affect related areas of chemosensory research, such as neural processing, downstream behaviours, and “in-silico” bioinformatics predictions of response profiles. The purity of standards is always implied but must be checked rigorously to prevent skewed or invalid results or conclusions, such as we exemplify here for Drosophila melanogaster and its olfactory receptor DmOr7a.

Coalescence of Bubbles with Mobile Interfaces in Water.

The fluid flow inside a thin liquid film can be dramatically modified by the hydrodynamic boundary condition at the interfaces. Aqueous systems can be easily contaminated by trace amounts of impurities, rendering the air-liquid interface immobile, thereby significantly resisting the fluid flow. Using high speed interferometry, rapid thinning of the liquid film, on the order of the collision speed, was observed between two fast approaching air bubbles in water, indicating negligible resistance and a fully mobile boundary condition at the air-water interface. By adding trace amounts of surfactants that changed the interfacial tension by 10^{-4} N/m, a transition from mobile to immobile was observed. This provides a fundamental explanation why the bubble coalescence time can vary by over 3 orders of magnitude.

Sustainable nutrients recovery and recycling by optimizing the chemical addition sequence for struvite precipitation from raw swine slurries

Livestock farming contributes heavily to nitrogen (N) and phosphorus (P) flows into the environment, a major cause of eutrophication of coastal and freshwater systems. Furthermore, the growing demand for N-P fertilizers is increasing the emission of anthropogenic reactive N into the atmosphere and the depletion of the current P reserves. Therefore, it is essential to minimize the anthropogenic impact on the environment and recycle the wasted N-P for agricultural reuse. This study focused on enhancing struvite (MgNH4PO4*6H2O) precipitation from raw swine slurries in batch and laboratory-scale reactors. Different chemical addition sequences were evaluated, and the best removal efficiency (E%) was obtained when the chemicals were mixed before the precipitation process. Struvite was detected at a pH as low as 6 (E%N-P∼50%), and high E%N-P was found at pH 7–9.5 (80–95%). Furthermore, air stripping was used in place of NaOH to adjust pH, returning the same efficiency as if only alkali had been used. XRD and FE-SEM analysis of the precipitate showed that the recovered struvite was of high purity with orthorhombic crystalline structure and only trace amounts of impurities from matrix organics, co-precipitation products (CaO and amorphous calcium-phosphates), and residuals of added chemicals (MgO).

Highly crystalline graphene formation from graphene oxides by ultrahigh temperature process using solar furnace

ABSTRACTThis work reports the efficient structural restoration of defective graphene oxide (GO) to a crystalline graphene by an ultrahigh temperature process at around 1800 °C achieved by a solar furnace. The GO samples were treated at high temperature by irradiating concentrated sunlight and focusing it on the sample under an inert nitrogen environment at atmospheric and reduced pressure. The structural restoration of GO was analyzed by Raman spectra, and the features of their D- and 2D-bands were remarkably improved at ultrahigh temperatures. The restoration was induced not by a photochemical reaction but dominantly by a thermally stimulated reaction. The process under reduced pressure gives rise to significantly better features in the Raman spectra than that of the atmospheric condition. This tendency shows that a trace amount of impurities contained in pure nitrogen gas are not negligible and attack the GO surfaces to induce considerable defects. These results indicate the superiority of the ultrahigh temperature process at reduced pressure for efficient GO restoration and the formation of highly crystalline graphene.

Efficient hierarchically structured composites containing cobalt catalyst for clean synthetic fuel production from Fischer–Tropsch synthesis

We report a straightforward preparation method to synthesize hierarchical composite consisting of TiO2-coated multi-walled carbon nanotubes (CNTs) decorating a macroscopic host structure of α-Al2O3. The obtained composite possesses moderate specific surface area and very open porous structure, as well as moderate interaction with active sites, which significantly improve the cobalt nanoparticles dispersion and the mass diffusion during the reaction. The Co/TiO2/CNT-α-Al2O3 (CoTiCNTA) catalyst is then used in the Fischer–Tropsch synthesis (FTS) process. This hierarchical catalyst achieves a FTS rate to C5+ of 0.80gC5+gcat−1h−1 along with a long-chain hydrocarbons (C5+) selectivity of 85%, which can be pointed out as the most outstanding noble promoter-free catalyst for the FTS process. The as-synthesized catalyst also exhibits an extremely high stability as a function of time on stream which is also one of the prerequisites for the development of future FTS catalysts, especially for the Biomass-to-Liquids process where trace amount of impurities and/or moisture could have an impact on the catalyst stability. The present work also introduces a new investigation methodology based on the use of zero field 59Co NMR, which allows one to map in a precise manner the cobalt active phase distribution and to correlate it with the FTS performance. It is expected that such technique would be extremely helpful for the understanding of the catalyst structure–performance relationship and for future optimization in the FTS process as well as in other fields of investigation where cobalt particles are involved.

Electrical, Chemical, and Electrochemical Properties of Double Perovskite Oxides Sr2Mg1–xNixMoO6−δ as Anode Materials for Solid Oxide Fuel Cells

The suitability of double perovskite oxides of composition Sr2Mg1–xNixMoO6−δ (SMNM, x = 0–0.9) as anode materials for solid oxide fuel cells (SOFCs) was evaluated. Single double perovskite structures could be obtained up to x = 0.9 in syntheses at ambient atmosphere. However, after reduction at 800 °C, trace amounts of impurities were detected in the sample with x = 0.9, suggesting that the upper limit for the Ni content (x) in SMNM is less than 0.9 under SOFC operating conditions. The electrical conductivity of SMNM increases with increasing Ni content because of the increase in the concentration of electronic defects, [MoMo6+5+′], and the decreased band gap energy, as revealed by first-principles calculations. The substitution of Ni can facilitate the charge-transfer process of the electrode reaction, decrease the polarization resistance, and thus increase the power density of a single cell. X-ray photoelectron spectroscopy and temperature-programmed reduction measurements were used to explain the reaso...

Trace amounts of impurities in electrolytic manganese metal by sector field inductively coupled plasma mass spectrometry

An analytical method, using sector field inductively coupled plasma mass spectrometry (SF-ICP-MS) for rapid simultaneous determination of Be, Na, Mg, Si, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, As, Sn, Sb, Pb and Bi in electrolytic manganese metal, was described. At the beginning, the samples were decomposed by HNO3 and H2SO4, and then analyzed by SF-ICP-MS. Most of the spectral interferences could be avoided by measuring in different mass resolution modes. The matrix effects due to the excess of sulfuric acid and Mn were evaluated. Correction of matrix effects was conducted by using the internal standard elements. The optimum condition for the determination was investigated and discussed. The detection limit is in the range of 0.001–0.169 μg/L. The current method is applied to the determination of trace impurities in electrolytic manganese metal. And experiments show that good results can be obtained much faster, more accurately and conveniently by current method.

New Lithium Copper Borates with BO3 Triangles: Li6CuB4O10, Li3CuB3O7, Li8Cu7B14O32, and Li2Cu9B12O28

Crystal structures of three new lithium copper borates, Li3CuB3O7, Li8Cu7B14O32, and Li2Cu9B12O28, and a new Li6CuB4O10 polymorph were solved by single-crystal X-ray diffraction. In all of the structures, the boron cations form BO3 triangles, which are connected with each other and with copper polyhedra only via corners in Li6CuB4O10 and Li3CuB3O7 and via both corners and edges in Li8Cu7B14O32 and Li2Cu9B12O28. The Li3CuB3O7 and Li8Cu7B14O32 compounds were synthesized as pure samples with only trace amounts of impurities; hence, their magnetic properties could be investigated and analyzed in terms of underlying magnetic couplings. Other compositions always represented multiphase mixtures. Li3CuB3O7 features infinite Cu,O chains formed by Cu2O6 units consisting of edge-shared CuO4 squares. Together with two apical oxygen atoms with long interatomic Cu-O distances of 2.7-2.8 Å, the Cu2O6 units form chains extended along the a axis. These pseudochains are responsible for strong anisotropic thermal expansion behavior. The temperature dependence of the magnetization between 4 and 380 K for Li3CuB3O7 could be fit well by a spin-dimer model. The magnetic susceptibility of Li8Cu7B14O32 showed a more complex temperature dependence, with two different Curie-Weiss regimes in the temperature range of 2-380 K.

Influence of synthesis route on physicochemical properties of nanostructured electrolyte material La0.9Sr0.1Ga0.8Mg0.2O3−δ for IT-SOFCs

Nanosized La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) has been synthesized by both gel-combustion method and solid state reaction method as an electrolyte material for IT-SOFCs. The effect of synthesis route on phase purity of the samples has been studied by X-ray diffraction technique. In the gel-combustion method, perovskite structure was formed at 1,200 °C with only trace amount of impurity and has an average crystallite size of 27 nm obtained by Scherrer’s equation. In solid state route, phase pure product was obtained only at the calcination temperature of 1,500 °C. The characteristics of the samples were also studied using FTIR, TG/DTA, Small angle X-ray scattering, BET surface area, thermal expansion measurements, and electrochemical impedance spectroscopy. The activation energy for oxide ion conduction of LSGM samples derived from Arrhenius plot is ~1.01 and 1.09 eV for gel-combustion and ceramic route, respectively. Linear increment of thermal expansion obtained by Dilatometry shows that there is no phase change at higher temperature in the sample. Sintered densities and microstructural features of the samples were also studied. The chemical compatibility of this electrolyte material has been studied with the perovskite oxide-based cathode material La0.6Sr0.4Co0.2Fe0.8O3−δ and NiO.

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% N2, 21% CO, 18% H2, 12% CO2, 2% CH4 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.

Effect of sulfates and chlorides on electrification by a noninductive process applicable to stratiform clouds

Laboratory investigations have been carried out to find the sign and magnitude of charge transfer during the collision between ice crystals and graupel in the presence of supercooled water droplets inside a cylindrical steel chamber kept inside the walk‐in cold room, which can reach a temperature of −30°C. The experiments were performed with pure water (Milli‐Q, 18.2 Megohms‐cm) and with a trace amount of ammonium sulfate and sodium chloride at different concentrations at low rime accretion rate (<0.1 g m−2 s−1), similar to stratiform clouds in the temperature range −6°C to −26°C. The cloud was composed of supercooled water and vapor was produced by boiling premixed solutions containing trace amount of impurities. The impurities are carried into the cloud by the bubble‐breaking mechanism. This way of introducing impurities is different from the earlier experiments. The experiments were carried out at a constant impact velocity of 2.2 m/s. At higher temperatures, the sign of the graupel charging during the ice crystal–graupel collision for pure water obeys that of earlier studies. With a trace amount of ammonium sulfate and sodium chloride, the sign of charge transfer is different from that of pure water. The effect of cloud droplet spectra on the sign of charge transfer for pure water were in agreement with earlier studies but differed for sodium chloride.

Environmentally Friendly Refining of Diamond-Molecules via the Growth of Large Single Crystals

Using a home-made transparent two-zone furnace, single crystals of diamond molecules (or diamondoids) up to ∼1 cm3 were grown under real time observation using the vapor transport technique. This process proved to be an environmentally friendly means of refining diamond molecules. Optical measurements were performed to evaluate the purity of diamond molecules before and after the process, which demonstrated that even a trace amount of impurities in commercial samples was successfully removed by our method. The thus-obtained high-purity single crystals will accelerate fundamental and applied research on diamond molecules in the solid state, especially in the field of optoelectronics.

Influences of O 2 concentration on NO reduction and N 2O formation in thermal deNOx process

Flow reactor experiment and chemical kinetic modeling were carried out to evaluate the influences of oxygen concentration on NO reduction and N 2O formation during thermal deNOx process for temperatures of 1073–1473 K. Increasing oxygen concentration in the reactant gas from 0.3 to 9.3% not only reduces the NO reduction potential and N 2O emission, but also lowers and widens the “temperature window” for NO conversion and N 2O formation. Trace amount of impurity O 2 leads to the lowest NO emission at a high temperature of 1373 K with low N 2O emission. Test reveals that high molar ratio NH 3/NO suppresses the reverse effect of oxygen and brings out high percentage of NO reduction at leaner environment. Chemical kinetic simulations using 4 detailed mechanisms display differing trends in the NO and N 2O dependence on O 2 and temperature. Rota 2000 model gives the best description of our experiments, but some assumptions made in this mechanism are not fully realistic. This study provides new experimental data on the less noticed N 2O, and raises a question about the understanding of the detailed elementary chemistry on the thermal deNOx process. Further work is still required for reasonable kinetic explanations.

Electronic conduction in nematic phase of small molecules

We investigated charge-carrier transport in the nematic phase of small molecules such as 2-phenylbenzothiazoles by time-of-flight experiments, in which the conduction mechanism has been considered to be ionic. As a result, we established the hole and electron transports in the nematic phase of highly purified samples: we found that there were two transits, namely, fast and slow transits, in less pure samples; the slow transit was attributed to ionic conduction originating from trace amounts of impurities and the fast transit was attributed to electronic conduction whose attribution was elucidated by mobility changes in the diluted samples with a hydrocarbon of $n$-tetradecane $(n{\text{-C}}_{14}{\text{H}}_{30})$. From these results, we conclude that the intrinsic conduction mechanism in the nematic phase of small molecules is ambipolar and electronic, irrespective of the size of the $\ensuremath{\pi}$-conjugate system of the core moiety. Thus, they provide a new insight into the conduction mechanism in fluidic materials.

Selective nickel and cobalt uptake from pressure sulfuric acid leach solutions using column resin sorption

Selective removal of Ni and Co, from a high pressure acid leach (HPAL) solution of a Brazilian laterite nickel ore that contains relatively high concentration of impurities, was carried out with an ion exchange chelating resin possessing iminodiacetic acid group (Amberlite IRC 748®). The resin was tested in column experiments. The experimental results showed that higher pH values improved the ion exchanger performance and higher nickel load capacities were achieved. Besides, increasing nickel concentration in solution, nickel uptake and selectivity were substantially improved. The breakthrough experimental curves also showed that many metals were immediately brokenthrough just after the initiation of the feed, while the breakthrough of Ni began later. These results suggested that it is feasible to purify HPAL solution recovering nickel selectively using the chelating resin Amberlite IRC748® if some specific conditions related to pH, flow rate and nickel concentration are applied. Removal of metals from the resin was successfully performed with HCl and H 2SO 4 solutions. Nickel was eluted concentrated more than 20 times its initial concentration in the feed solution, while only a trace amount of impurities was eluted.

Role of trace impurities in large-volume noble gas atmospheric-pressure glow discharges

A computational study of capacitively coupled atmospheric-pressure glow discharges in high-purity helium is presented, and the role of trace impurities in such noble gas plasmas is established. Trace impurities result in generation of significant amounts of charged species through Penning ionization and charge exchange reactions. The altered charged species balance in the plasma causes a large change in the discharge impedance when compared to a completely pure noble gas discharge. Peak electron temperatures of the order of 50 000 K and electron densities of order 1011 cm−3 are predicted. Significant electron generation is observed inside the sheath region due to the highly collisional nature of the plasma. This study underscores the importance of modeling the effect of even trace amounts of impurities in noble gas atmospheric-pressure glow discharges.

Interfacial Acid−Base Reactions of Aluminum Oxide Dispersed in Aqueous Electrolyte Solutions. 1. Potentiometric Study on the Effect of Impurity and Dissolution of Solid Phase

A pyrogenic alumina (type C, Degussa) was studied. The original product contains chlorine impurity (∼1 × 10-4 mol/g), the hydrolysis of bound chlorine results in acidic species in aqueous suspension. Heat treatment at 1000 °C proved to be an effective purification. Potentiometric acid−base titration was used to characterize the surface charging of alumina in electrolyte solutions (KNO3, KCl). This method can measure only the H+/OH- depletion in bulk liquid phase. Trace amounts of impurity and additional acid−base reactions, such as dissolution of solid, affect the net H+/OH- consumption. We analyzed these effects on proton adsorption curves. The fitting (FITEQL) of titration data for purified alumina in KNO3 solutions between pH ∼5 and ∼9 is good enough with assuming surface charging reactions only and using any surface complexation model. In KCl solutions, however, only the triple layer model resulted in an acceptable optimization, presumably because of the specific adsorption of Cl- ions. Outside these material-specific limits of pH, asymmetric proton binding curves appear which are often interpreted as a result of specific ion adsorption or surface site heterogeneity. In fact, the dissolution of the amphoteric solid plays the governing role, especially below pH ∼4.5. The experimental curves over the range of pH 3−10 can be fitted well, if the partial dissolution of alumina and the solution equilibria of mononucleus Al-species formation with literature log K values are inserted into the model, in addition to the surface complexation. The assumed chemical model can be supported only by an independent analysis of equilibrium liquid phase. The concentration of aluminum in the equilibrium supernatants with different pH values between ∼4 and ∼10 were measured by means of the inductively coupled plasma method. The measured amounts coincide strikingly well, especially in the alkaline region, with the calculated total concentration of Al species, which provide indisputable evidence for the reality of the assumed chemical model.

Decomposition of polypropylene hydroperoxides induced by nitric oxide: New concept of reaction mechanism

NO-induced decomposition of hydroperoxides in solid polypropylene and cumyl hydroperoxide, dissolved in n-decane, at 25°C was studied. Analysis of kinetic regularities of hydroperoxide decomposition and nitroxide radical accumulation leads to the conclusion that both in solids and in solutions these reactions have the autoaccelerated character. The induction periods are determined by trace amounts of impurities (probably of higher nitrogen oxides).The maximum rate of the process depends on the NO pressure. The possible reaction mechanisms are supposed, and the key role is assigned to the formed nitrosocompounds.