NO x -Catalyzed Gas-Phase Activation of Methane: In Situ IR and Mechanistic Studies

The products of reactions occurring in a CH₄–O₂–NO _x mixture have been investigated by in situ FTIR spectroscopy. The results show that low temperatures favor the formation of HCHO and CH₃OH, while high temperatures favor that of C₂H₄. Possible reaction mechanisms based on the in situ observations are briefly discussed.     

Non-Isothermal NOx Storage/Release over Manganese Based Traps: Mechanistic Considerations

The NO storage properties of MnO _x /support materials (5–50 wt% MnO _x loading) was experimentally investigated in the presence of O₂ and H₂O between 50 and 700 °C applying a non-isothermal temperature-programmed method. In dependence on MnO _x loading and NO supply, the materials show an intermediate decrease of NO storage capacity between 200 and 300 °C. This effect is caused by decomposition of surface nitrites with release of NO into the gas phase as proved by in situ DRIFT measurement. The interpretation is corroborated by modelling of the underlying adsorption/desorption reaction steps, considering the different thermal stability of nitrite/nitrate surface species.     

FA selectivity of lipases in acyl-transfer reactions with acetate esters of polyols in organic media

FA reaction selectivity of Burkholderia cepacia, Rhizomucor miehei, and Candida antarctica fraction B lipases was compared between acyl-transfer and esterification reactions. Multicompetitive reaction mixtures containing a series of n-chain FA (a C₄–C₁₈ series; and a C_18∶x series, where X=0-3 double bonds) and a single acetate ester co-substrate [triacetin, 1,2-propanediol (1,2-PD)diacetate, and 1,3-PD diacetate] were studied in tert-butyl methyl ether at an a _w of 0.69. For B. cepacia lipase, FA optima for C₈, C₁₆, and C_18∶2 were observed in all reactions with 1.0- to 5.9-fold differences in FA selectivity. For R. miehei lipase, an optimum for C₈ FA was observed in all reactions with 1.2- to 6.7-fold differences in FA selectivity. For C. antarctica lipase, FA optima for C₈/C₁₀ were observed in all reactions with 1.0- to 2.8-fold differences in FA selectivity. FA selectivities were broadly modulated upon changing from free polyol to acetate ester co-substrates for B. cepacia and R miehei lipases, whereas FA selectivity modulations were more specific upon this change in reaction configuration for C. antarctica B lipase. For all lipases, reactivity toward unsaturated C_18∶x FA was enhanced in acyl-transfer relative to esterification reactions with these polyol co-substrates.     

Nafion®/(SiO2, ORMOSIL,and dimethylsiloxane) hybrids via in situ sol–gel reactions: Characterization of fundamental properties

Nafion®/SiO₂, Nafion®/[ OR ganically MO dified SIL icate (ORMOSIL)] and Nafion®/dimethylsiloxane hybrids were created via in situ sol–gel reactions for tetraethoxysilane, diethoxydimethylsilane, and their mixtures. Differential scanning calorimetry studies showed a broad endotherm for unfilled Nafion®-H⁺ at T_α ≈ 215°C that shifts upward for the Q : D = 1 : 0 (mol : mol) [Q = Si(O_1/2)₄, D = (O_1/2)₂Si(CH₃)₂] hybrid, then shifts downward with decreasing Q : D. This endotherm likely arises from release of H₂O molecules bound to ≡Si—OH groups and condensation reactions among silanol groups. The decrease in T_α is rationalized in terms of an increasing fraction of flexible D units that disrupt hydrophilic Q structures. T_m shifts to lower temperatures with decreasing Q : D, and it is suggested that main chains are restricted by side chains embedded in silicon oxide nanoparticles, but D unit insertion causes side chains to be anchored less strongly. Thermal gravimetric analysis indicates that the first mass loss step for Nafion®-H⁺ shifts to higher temperatures as D : Q increases; an increase in D unit fraction inhibits Q unit degradation by evolved HF. A dynamic mechanical transition at T_α may arise from side chain motions, and the increase in T_α in passing from unfilled Nafio®-H⁺ to the 1 : 0 hybrid is due to side chain immobilization by their entrapment in silicon oxide domains. The progression 0 : 1 → 1 : 2 → 1 : 1 → 2 : 1 generates increasing mechanical tensile strength and decreasing ductility; strength enhancement might be due to entanglements between ORMOSIL and pure silicon oxide phases and side chains. Liquid sorption experiments quantified the affinity of these hybrids for solvents of varying polarity. A dielectric relaxation for the 0 : 1 hybrid at about 1.5 kHz might be related to side chain mobility. A weaker relaxation in the range 10⁴–10⁵ Hz exists for the 0 : 1 and 1 : 1 hybrids and Nafion®-H⁺, but not for the 1 : 0 hybrid that exhibits the behavior ε′ ∼ f⁻ⁿ over a broad frequency (f) range, suggestive of intercluster proton hopping. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:747–763, 1998     

Synthesis of a new 2D fluorogallophosphate intercalated by double organic sheets of morpholine

One way to obtain new materials is to exploit the in situ generation of the structure-directing agent. By this synthetic route, solvents or precursors of the templates are introduced into the starting mixtures, and during the synthesis, they partly decompose into molecules that act as templates. This paper deals with the synthesis of a fluorogallophosphate with a new template precursor, the N-formylmorpholine. This compound, used as main solvent, is unstable in acidic media. At high temperature it decomposes and generates in situ the morpholine molecules. We report the structure of a two-dimensional fluorogallophosphate named Mu-38 structurally related to ULM-9. This compound Ga₃P₃O₁₂F₃[C₄H₁₀NO]₃ (Z = 4) consists of anionic inorganic layers containing single four rings units linked and charge-balanced by protonated morpholine. It was also characterized by powder XRD, SEM, elemental and thermal analyses, and solid state NMR spectroscopy (¹³C, ¹⁹F and ³¹P MAS and ³¹P CP MAS experiments).     

Integrating legumes to improve N cycling on smallholder farms in sub-humid Zimbabwe: resource quality, biophysical and environmental limitations

The release of mineral-N in soil from plant residues is regulated by their ‘quality’ or chemical composition. Legume materials used by farmers in southern Africa are often in the form of litter with N concentration <2%. We investigated the decomposition of Sesbania sesban and Acacia angustissima litter in the field using litterbags, and N mineralization of a range of legume materials using a leaching tube incubation method in the laboratory. The mass loss of the litter could be described using a modified exponential decay model: Y = (Y ₀−Q)e^−kt + Q. The relative decomposition constants for Sesbania and Acacia litter were 0.053 and 0.039 d⁻¹, respectively. The % N mineralized from fresh Sesbania prunings was 55% compared with only 27% for the Sesbania litter after 120 days of incubation under leaching conditions. During the same period, fresh prunings of Acacia released only 12% of the added N while Acacia litter released 9%. Despite the large differences in N concentration between Acacia prunings and its litter, the total mineralized N was similar, as mineralization from prunings was depressed by the highly active polyphenols. While N supply may be poor, these slow decomposing litter materials are potentially useful for maintaining soil organic matter in smallholder farms. In two field experiments with contrasting soil texture, Sesbania, Acacia and Cajanus produced large amounts of biomass (>5 Mg ha⁻¹) and improved N cycling significantly (>150 kg N ha⁻¹) on the clay loam soil, but adapted poorly on the sandier soil. There was a rapid N accumulation in the topsoil at the beginning of the rains in plots where large amounts of Sesbania or Acacia biomass had been incorporated. Despite the wide differences in resource quality between these two, there was virtually no difference in N availability in the field as this was, among other factors, confounded by the quantity of N added. A substantial amount of the nitrate was leached to greater than 0.4 m depth within a three-week period. Also, the incidence of pests in the first season, and drought in the second season resulted in poor nitrogen use efficiency. Our measurements of gaseous N losses in the field confirmed that N₂O emissions were <0.5 kg N ha⁻¹. As we had measurements of all major N flows, we were able to construct overall N budgets for the improved fallow – maize rotation systems. These budgets indicated that, in a normal rainfall season with no major pest problems, reducing nitrate leaching would be the single largest challenge to increased N recovery of added organic N in the light textured soils.     

Ozone Degrades Common Herbivore-Induced Plant Volatiles: Does This Affect Herbivore Prey Location by Predators and Parasitoids?

Inducible terpenes and lipoxygenase pathway products, e.g., green-leaf volatiles (GLVs), are emitted by plants in response to herbivory. They are used by carnivorous arthropods to locate prey. These compounds are highly reactive with atmospheric pollutants. We hypothesized that elevated ozone (O₃) may affect chemical communication between plants and natural enemies of herbivores by degrading signal compounds. In this study, we have used two tritrophic systems (Brassica oleracea–Plutella xylostella–Cotesia plutellae and Phaseolus lunatus–Tetranychus urticae–Phytoseiulus persimilis) to show that exposure of plants to moderately enhanced atmospheric O₃ levels (60 and 120 nl l⁻¹) results in complete degradation of most herbivore-induced terpenes and GLVs, which is congruent with our hypothesis. However, orientation behavior of natural enemies was not disrupted by O₃ exposure in either tritrophic system. Other herbivore-induced volatiles, such as benzyl cyanide, a nitrile in cabbage, and methyl salicylate in lima bean, were not significantly reduced in reactions with O₃. We suggest that more atmospherically stable herbivore-induced volatile compounds can provide important long-distance plant-carnivore signals and may be used by natural enemies of herbivores to orientate in O₃-polluted environments.     

Study of (La,Sr)(Ti,Ni)O3-δ materials for symmetrical Solid Oxide Cell electrode - Part B: Conditions of Ni exsolution

The stability of La_2xSr_1-2xTi_1-xNi_xO_3-δ (LSTN) and La_7x/4Sr_1-7x/4Ti_1-xNi_xO_3-δ (25LSTN) materials in high temperature reducing conditions has been studied with a special focus on the Ni exsolution process for SOFC anode / SOEC cathode application. In a general way, LSTN and 25LSTN compounds are stable after treatments at 800 °C in air and wet reducing atmosphere. The low chemical expansion makes them compatible with a use in an electrochemical Solid Oxide Cell. Those materials are therefore useful for an application as symmetric oxide cell electrode or only hydrogen electrode. In situ Nickel exsolution is evidenced at 800 °C in Ar/H₂(2%) but is limited by a slow kinetics and a higher temperature pre-reduction is preferred before a use as SOFC anode (SOEC cathode). Depending on the treatment, in situ reduction or pre-reduction (T>1000 °C), the compounds are not in the same thermodynamic equilibrium state.     

All-solid-state complementary electrochromic windows based on the oxymethylene-linked polyoxyethylene complexed with LiClO4

Oxymethylene-linked polyoxyethylene complexed with LiClO₄ at a Li/EO molar ratio of 0.05 has a conductivity of 4.7 × 10^-4 S•cm^-1 at 25°C and a transmittancy of 90%. It is a promising electrolyte for an all-solid-state complementary electrochromic window using WO₃ and NiO_x. The modulation depth of the window exceeds 50% from 700 nm to 900 nm. The electrochromic ability of the window increases with temperature and lithium salt concentration and the window also exhibits good storage property under open circuit. Current and optical responses of the window as well as the electro-chromic process are also discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1739–1744, 1997     

A Straightforward Synthesis of Enantiomerically Pure trans‐2, 5‐Bis(alkyloxymethyl) pyrrolidines by 1, 3‐Dipolar Cycloaddition Reactions of Azomethine Ylides

A new efficient method for the stereoselective preparation of trans‐2,5‐bis(alkyloxymethyl)pyrrolidines ( 7 ) using easily available starting materials is described. The main step of this synthesis is the stereoselective formation of the pyrrolidine ring by the 1,3‐dipolar cycloaddition reaction of an in situ generated azomethine ylide. Both enantiomers of the C₂‐symmetric auxiliaries are prepared separately in a short reaction sequence.     

New effective process to fabricate fast switching and high contrast electrochromic device based on viologen and Prussian blue/antimony tin oxide nano-composites with dark colored state

We developed a new electrochromic device by using compact Prussian blue (PB)/antimony tin oxide (ATO) nano-composites as anodic electrode and viologen anchoring on titanium dioxide (TiO₂) nano-particles as cathodic electrode. The anodic electrode was based on a transparent nanostructured ATO nano-particle film and was electro-deposited by Prussian blue to form compact Prussian blue/ATO nano-composites by means of galvanostatic electrodeposition process. Nanocrystalline TiO₂ thin films on conducting glass were modified with a mono-layer of viologen with two anchoring groups, which were much strongly adsorbed onto the surface of TiO₂ nano-particles. A polymer gel electrolyte sandwiched between the anodic and cathodic layers is used as the ionic transport layer. The 2.5 cm × 2.5 cm electrochromic device shows high contrast (64.8%, at 600 nm) very low transmittance at colored stage (0.1%, at 600 nm), fast switching time (600 and 720 ms for coloration and bleaching, respectively), high coloration efficiency of 912 cm² C⁻¹ at 600 nm and good stability. The enhanced performance of the electrochromic device can be attributed to the ATO nano-particles as inter-conductive materials.     

Electrochemical and chemical investigations of the co-polymers of 3-aminobenzenesulfonic acid with aromatic amines for their application in electrochromic devices

The chemical oxidative polymerization and electrochemical polymerization of 3-aminobenzenesulfonic acid with aromatic amines have been carried out in p-toluenesulfonic acid which acts as a supporting electrolyte as well as an external dopant. The presence of –SO₃H groups in the ABSA co-monomer allows the copolymer to acquire intrinsic protonic doping ability. The electrochemically synthesized polymers and copolymers have been characterized by cyclic voltammetry for analyzing the growth of copolymers and chronoamperometry studies for their applications to the electrochromic devices. In addition to construction of electrochromic devices (ECDs), the electrochromic properties of the polymer films were further investigated. Electrochromic switching stability of the devices was estimated from switching times between their oxidized and reduced states, which indicates that the homopolymers and copolymer can be used for promising electrochromic devices. Chemically synthesized copolymers were also characterized using various techniques like Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy and electrical conductivity at room temperature.     

Bifunctional Catalysts Stabilized on Nanocrystalline Magnesium Oxide for One‐Pot Synthesis of Chiral Diols

New bifunctional catalysts composed of PdCl₄²⁻, OsO₄²⁻ and OsO₄²⁻, WO₄²⁻ designed and prepared by a counterionic stabilization technique involving the reactions of Na₂PdCl₄‐K₂OsO₄ and K₂OsO₄‐Na₂WO₄ with nanocrystalline MgO are well characterized. These bifunctional catalysts, NAP‐Mg‐PdOs and NAP‐Mg‐OsW perform tandem Heck asymmetric dihydroxylation and asymmetric dihydroxylation‐N‐oxidation reactions, respectively, in the presence of the chiral ligand 1,4‐bis(9‐o‐dihydroquinidinyl)phthalazine [(DHQD)₂PHAL] in a single pot. It is quite impressive to note that H₂O₂ is used as a terminal oxidant to provide N‐methylmorpholine N‐oxide (NMO) in situ by the oxidation of N‐methylmorpholine (NMM) in the asymmetric dihydroxylation‐N‐oxidation catalyzed by NAP‐Mg‐OsW.     

Smart sunglasses based on electrochromic polymers

Smart sunglasses based on electrochromic polymers are proposed and developed in this study. This article discusses the design, processing, and the optical and electrical performance of a prototype smart sunglasses based on cathodic electrochromic (EC) polymers, which show several merits compared with traditional materials for sunglasses lens as well as other smart window materials. It is a multilayer design of device. The conjugated polymer, poly[3,3‐dimethyl‐3,4‐dihydro‐2H‐thieno [3,4‐b] [1,4]dioxepine] (PProDOT‐Me₂), is utilized as the electrochromic working layer. The counter layer of the device is vanadium oxide (V₂O₅) film, which serves as an ion storage layer. There is also a polymer gel electrolyte acting as the ionic transport layer, sandwiched between the working and counter layers. The characteristics of the prototype device are reported, including transmittance (%T), driving power, response time, open circuit memory, and lifetime. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

The dynamic surface chemistry during the interaction of CO with ceria captured by Raman spectroscopy

The interaction of CO with ceria under conditions typically used to measure the oxygen storage capacity (OSC) of automotive three way catalysts (TWC) has been investigated by in situ Raman spectroscopy. During exposure of the ceria to CO at 623 K vibrational bands at 1582–1600 and 1331–1340 cm⁻¹ appeared; these bands increased with increasing time of exposure to CO. The band positions are consistent with phonon modes of carbon; however, assignment to carboxylate species or carbonate species cannot be excluded. Subsequent exposure to O₂ at room temperature resulted in a decrease in the intensities of the 1582–1600 and 1331–1340 cm⁻¹ bands by more than 90%. As well, exposure to O₂ at room temperature also resulted in the appearance of Raman modes characteristic of formate and peroxide surface species. The mechanism by which formate forms upon room temperature O₂ exposure is discussed in the context of the assignment of the 1582–1600 and 1331–1340 cm⁻¹ bands to carbon phonon modes which result from the disproportionation of CO on reduced ceria.     

Iridium Clusters for Catalytic Partial Oxidation of Methane—An In Situ Transmission and Fluorescence XAFS Study

In situ transmission and fluorescence EXAFS combined with on-line gas analysis have provided new insight in the structural changes and the catalytic properties of Ir clusters during the catalytic partial oxidation (CPO) of methane. A novel in situ fluorescence XAFS setup with a multi element silicon drift detector allows time-resolved in situ studies on catalysts with small noble metal concentrations. Significant structural differences were found between a 0.5 wt% Ir/Al₂O₃ and a 2.5 wt% Ir/Al₂O₃ catalyst upon treatment in He and H₂. After He treatment metallic clusters form on high loading Ir catalysts but not when the loading is small. Upon H₂ treatment metallic Ir clusters are detected in both catalysts, but the particle size is smaller when a low loading is used. The smaller clusters appear to be more sensitive to oxidation. The CPO reaction is found to ignite at 320°C, nearly independent of the residence time and the Ir cluster size. The structure of the clusters changes significantly at the ignition point. Below the ignition point they are partly (2.5 wt% Ir) or nearly fully (0.5 wt% Ir) oxidized and above the ignition temperature they are abruptly reduced. The catalytic and structural changes are reversible.     

Effects of preparation methods of support on the properties of nickel catalyst for hydrogenation of m-dinitrobenzene

Using tetraethyl orthosilicate (TEOS) as the precursor of silica, the silica aerogel and xerogel, which were used as supports of nickel-based catalysts for liquid hydrogenation of m-dinitrobenzene to m-phenylenediamine, were prepared by the sol-gel method combined with supercritical drying (SCD) and conventional drying, respectively. Then, a series of nickel-based catalyst samples supported on these supports were prepared by the incipient wetness impregnation method with an aqueous solution of nickel nitrate as well as lanthanum nitrate as impregnation liquids. Based on the characterization results of nitrogen adsorption-desorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature-programmed desorption of hydrogen (H₂-TPD), and catalytic activity evaluation, the physico-chemical properties and catalytic performances of the catalysts were investigated. The results show that the nickel crystallites on the binary nickel catalyst using silica aerogel as support are of smaller particle size. However, compared with the sample supported on silica xerogel, the nickel catalyst supported on the silica aerogel exhibits lower activity and selectivity for the hydrogenation of m-dinitrobenzene because it has a lesser amount of active sites and weaker absorption ability to reactants caused by sintering of the nickel crystallites. The addition of promoter La₂O₃ could increase the activity and selectivity of the catalysts. Among all the nickel-based catalyst samples prepared, the La₂O₃ promoted ternary nickel-based catalyst supported on silica xerogel exhibits the highest activity and selectivity for the hydrogenation of m-dinitrobenzene to m-phenylenediamine, which could be attributed to its highest active surface area and appropriate absorption strength to reactants. Over this promising catalyst, the conversion of m-dinitrobenzene and the yield of m-phenylenediamine could reach 97.0% and 93.1%, respectively, under proper reaction conditions of hydrogen pressure 2.6 MPa, temperature 373 K, and reaction time 1 h. Translated from Journal of Chemical Engineering of Chinese Universities, 2006, 20(5): 723–727 [译自: 高校化学工程学报]     

Stability-enhanced indium hexacyanoferrate electrodes: Morphological characterization, in situ EQCM analysis in nonaqueous electrolytes and application to a WO3 electrochromic device

This paper presents a promising transparent counterelectrode system for a WO₃ electrochromic device (ECD) on the basis of a stability-enhanced indium hexacyanoferrate (InHCF) electrode and a NaClO₄/propylene carbonate (PC) electrolyte. Through SEM characterization it was found that clusters of granular InHCF nanoparticles (ca. 80-140 nm) were deposited on ITO substrates in HCl and KCl-stabilized plating solutions, and uniform micrometer thick films with high charge capacity could be obtained. From in situ electrochemical quartz crystal microbalance study, it was discovered that Na⁺ would enter or move out from the InHCF film in the “desolvated” form during the redox process in a PC electrolyte. Besides, NaClO₄/PC resulted in higher electrochemical activity and reversibility than LiClO₄/PC. With these discoveries, a durable WO₃-InHCF ECD featuring blue-to-colorless electrochromism was fabricated successfully. The device remained 73.6 and 88.7% of its initial ΔT values at 600 and 800 nm after 40,000 rapid and successive coloring/bleaching cycles, respectively. Moreover, the cycling-induced loss of electrochromic performance almost completely restored after 1-month rest and kept unchanged for another month. Thus, the applicability of this nonaqueous InHCF counterelectrode system to ECDs was verified.     

Mixed oxygen ionic-carbonate ionic conductor membrane reactor for coupling CO2 capture with in situ methanation

CO₂ methanation is one of the vital reactions to utilize CO₂ and realize power to gas process. To decrease the CO₂ capture cost and alleviate the hot spots during the strong exothermic methanation reaction, here, we report a coupling of CO₂ capture process with in situ CO₂ methanation process through a ceramic-molten carbonate (MC) dual phase membrane reactor over the Ni-based catalyst. The performance of the membrane reactor was systematically investigated and compared with the traditional fixed-bed reactor. The results show that the performance of the membrane reactor is higher than that of the fixed-bed reactor, since the produced steam through the methanation process can be partially removed through the dual-phase membrane, which promotes the reaction shift to right side. A stability test shows no obvious degradation within 32 h. These results indicate that the membrane reactor is promising for coupling CO₂ capture with in situ methanation process.