Catalytic NO–H2–CO–O2 reactions over Pt-supported mesoporous yttrium oxide

Catalytic light-off of a stream of NO, H₂, CO in an excess O₂ has been studied over various metal oxides loading 1 wt% Pt. Because a low-surface area Y₂O₃ (<5 m² g⁻¹) was found to exhibit the highest de-NO_x activity, a mesoporous Y₂O₃ was then synthesized from an yttrium-based surfactant mesophase templated by dodecyl sulfate , which was anion-exchanged by acetate (AcO = CH₃COO⁻). The product showed a 3-D mesoporosity with a large surface area (396 m² g⁻¹) and the Pt-supported catalyst achieved much improved light-off characteristics suitable for the low-temperature de-NO_x in the presence of CO and excess O₂.     

Preparation and reaction mechanistic characterization of sol–gel indium/alumina catalysts developed for NO x reduction by propene in lean conditions

The impregnation and sol–gel preparation methods were investigated to develop high activity catalysts and understand the significance of the indium–aluminium interaction on aluminasupported indium catalysts in NO _x reduction with propene. Active In/alumina catalysts with a very high surface area (270 m²/g) and thermal stability were prepared in controlled conditions by sol–gel processing. When Al isopropoxide and In nitrate in ethyl glycol were used as precursors in aqua media, indium atoms were incorporated evenly distributed as a thermally stable form in the aluminium oxide lattice structure. In wet impregnation it was beneficial to use a certain excess of aqueous In solution (volumes of solution : pores = 2 : 1) to have the highest NO _x reduction activity. The catalyst containing dispersed Al on In oxide (58 wt% In, phaseequilibrium preparation method) showed activity at lower temperatures than any other In–Al oxide catalyst or pure In₂O₃. The adsorption of different reaction intermediates on alumina and stable In₂O₃ sites were detected by FTIR studies. In/alumina catalysts have active sites to oxidize NO to NO₂, partially oxidize HC, form the actual reductant which contains N–H or N–C bonding and react with NO to dinitrogen. The cooperation with indium and aluminium was evident even in the mechanical mixture of sol–gel prepared alumina (301 m²/g) and In₂O₃ powders (27 m²/g), where the probability for molecularscale intimate contact between indium and aluminium sites was very low (particle size 10–250 m). Shortlived gaseous intermediates and surface migration are the possible reasons for the high catalytic activities on the two physically separated active sites both necessary for the reaction sequence.     

Application of the Bifunctional Switch-Type Cryptand Ion Chromatographic Stationary Phase for Ion Separation

ABSTRACT

Poly(styrene/divinylbenzene) resin with cryptand 22 as an anchoring group was synthesized and applied in ion chromatography as a packing material for separations of organic anions as well as cations. The cryptand can not only form strong complexes with metal cations, but it has also shown a remarkable complexing ability with organic anions after protonation at pH < 7. The protonated cryptand resin has been applied as an anion exchanger to successfully separate some organic carboxylate anions including HCOO^?, CH₃COO^?, CH₃CH₂COO^?, and some geometric isomers, e.g., fumarate and maleate ions, with water as the eluent. Alternatively, after deprotonated at pH > 7, the cryptand resin can be switched as a cation exchanger to separate inorganic cations. The effects of solvents, temperature, pH values, and flow rates of eluents on the separation of organic anions were also investigated.     

Crown ether bridged homo- and heterodinuclear copper(II) and nickel(II) cyclidene complexes: Interaction with anions

Homodinuclear (3CuCu, 3NiNi) and heterdionuclear (3CuNi) cyclidene complexes linked by two 1,10-diaza-18-crown-6 ethers were synthesized and their properties characterized. For the 3CuCu in the negative potential range the mixed-valence state Cu^I-Cu^II was observed and the comproportionation constants were determined. The redox potentials of M^II/III showed a good correlation with DN of the solvent. In acetonitrile solution containing 0.1 mol dm⁻³ Bu₄NPF₆ reversible M^II/III redox processes were observed. However, in the presence of stronger ion pairing anions (e.g. BF₄⁻ and ClO₄⁻) the “potential inversion” occurred. Redox potentials of dinuclear complexes were compared with mononuclear cyclidene complexes. The influence of selected anions (Cl⁻ and NO₃⁻) on the redox process M^II/III was studied. The effect of Cl⁻ anion was different for 3CuCu and 3NiNi. In 3CuCu coordination of two chloride anions took place after oxidation of copper centers. In the 3NiNi complex two Cl⁻ anions were coordinated to one of the nickel(II) centers facilitating oxidation, at different potentials, of both nickel(II) cations. The behaviour of heteronuclear complex with Cl⁻ anions was similar to 3NiNi. All dinuclear complexes interacted with NO₃⁻ anions and the observed potential shifts were larger for nickel(II) than for copper(II) cations.     

Mechanochemical block copolymerization in heterogeneous systems of the solid polyethylene with acrylamide aqueous solutions by ultrasonic irradiation

Summary Mechanochemical block copolymerization in heterogeneous systems of the solid polyethylene-acrylamide-sodium dodecyl sulfate aqueous solutions has been studied by ultrasonic irradiation at 30 °C. An additional effect of the solid polyethylene and the effects of acrylamide, and sodium dodecyl sulfate concentrations on mechanochemical block copolymerization were investigated. The block copolymerization of acrylamide was initiated by free radical produced from the polyethylene particles by ultrasonic waves. The rate of copolymerization R _p increased with increasing additional amount of polyethylene and that value was of the order of 10^-3 mol/l s. In addition, the R _p was given by R _p [Acrylamide] [Sodium dodecyl sulfate].     

Anionic Clays as Potential Slow-Release Fertilizers: Nitrate Ion Exchange

Several nitrate containing anionic clays were synthesized at different temperatures and the kinetics of NO₃ ^– release were determined to test their suitability as slow-release N fertilizers. A sample (Mg:Al = 2:1) synthesized at 60°C with smaller particle size released 75, 86 and 100% of its NO₃ ^– in 1, 3 and 7 days, respectively when equilibrated with a simulated soil solution. On the other hand, the 175°C/2 hrs sample with larger particle size released 65, 77 and 84% of its nitrate in 1, 3 and 7 days, respectively. Another anionic clay (synthesized at 175°C/24 hrs) of higher charge density (Mg:Al = 2:1) containing NO₃ ^– was equilibrated with a 0.012 N NaCl or Na₂CO₃ to test the role of different anions in releasing the NO₃ ^– anion from the interlayers. The results showed that Cl^– released more NO₃ ^– than did CO₃ ^2– from this anionic clay after all the treatment times probably as a result of the CO₃ ^2– anion blocking the release of NO₃ ^– from the interior of the crystals. When a lower charge density (Mg:Al = 3:1) sample (synthesized at 175°C/48 hrs) was equilibrated with 0.02N solution of anions the release of nitrate was as follows: Cl^– < F^– < SO₄ ⁼ CO₃ ^2–. These results suggest that the divalent SO₄ ⁼ and CO₃ ^2– anions are more effective in the release of NO₃ ^– from this lower charge density anionic clay. Time-resolved structural analysis of NO₃ ^– exchange with CO₃ ^2– in the above anionic clay using synchrotron x-ray diffraction showed that ion exchange is rapid because of small crystal size and lower charge density. Thus the release of NO₃ ^– from anionic clays is an interplay among the type of anions present in soil solution, their concentration, pH of soil solution, the charge density and crystal size of anionic clay etc.     

Photocatalytic removal of methyl orange in an aqueous solution by a WO3/TiO2 composite film

WO₃/TiO₂ composite film was prepared by microarc oxidation technique and characterized by SEM, XRD, UV-vis spectra and Zeta-potential. The photocatalytic activity of WO₃/TiO₂ composite film was evaluated by examining the degradation of methyl orange. The influence of solution pH and inorganic anions on removal ratio of methyl orange was investigated. Removal ratio of methyl orange decreased with an increase of pH value in acidic solution, while it increased with the pH value in alkaline solution. The influence of added anions on the removal ratio is divided into two aspects. Addition of Cl^? and SO ₄ ^2? resulted in a decrease in photocatalytic removal ratio of methyl orange, while it was facilitated by PO ₄ ^3? , HCO ₃ ^? and NO ₃ ^? .     

Bis-imidazolium type ion-exchange resin with poly(HIPE) structure for the selective separation of anions from aqueous solutions

ABSTRACT

The aim of this work was to obtain and characterize the selectivity of a new type of ion-exchanger – porous highly basic monolith with high internal phase emulsion (HIPE) structure. Poly(HIPE)ViM monolith of bis-vinylimidazolium salts was prepared in a water-in-oil-in-water emulsion (W₁/O/W₂). The structure of the resulting HIPE polymer was confirmed using scanning electron microscopy (SEM). Ion-exchange ability and the selectivity of monolithic anion-exchanger were tested towards the following inorganic anions: F^?, Br, Cl^?, NO₃^?, SO₄^2-, Mo₇O₂₄^6-, PO₄^3-; and organic anions: malate, citrate, malonate, tartate, lactate and oxalate. The concentration of anions before and after the sorption was measured using ion chromatography.     

Nitrate and nitrite electrocatalytic reduction on Rh-modified pyrolytic graphite electrodes

The electrochemical reduction of nitrate and nitrite anions was investigated on Rh-modified pyrolytic graphite electrodes prepared by potentiostatic electrodeposition with the use of a double-pulse technique. Several important parameters (pH, temperature and composition of electrolytic medium, electrolysis potential) were varied. Only ammonia and nitrite ions were detected among NO₃⁻ reduction products, while NO₂⁻ ions are straightforwardly reduced to ammonia. The experimental data (CV measurements and the results of electrolyses) clearly show that Rh/graphite electrodes are much more efficient for NO₂⁻ reduction than for that of NO₃⁻ at room temperature which was confirmed by the determination of rate constants of corresponding reactions and the activation energy of NO₂⁻ reduction. The influence of carboxylate anions and tetraalkylammonium cations on the electrocatalytic activity of Rh/graphite electrodes was investigated and the inhibiting effect of HCOO⁻ anions on hydrogen evolution reaction and nitrate reduction was demonstrated.     

Characterization of metal-ion containing polyesters

Summary The glass transition behavior of poly(diethylene glycol-co-succinic acid) (DEGSA) and its complexes obtained in the reaction with MgO have been investigated. The number average molar mass ( ) of the DEG-SA samples prior to complexation was determined by titration of the terminal COOH groups. The glass transition temperature (T_g) was measured as a function of molar mass and Mg²⁺ ion content. The dependence of T_g on obeyed the Fox-Flory relationship. Addition of increasing amounts of MgO to DEG-SA led to a gradual increase in T_g, and a decrease in the heat capacity change (c_p). This behavior is associated with complex formation between COO^-and Mg²⁺. The decrease in c_p is a result of ion-ion and to a lesser extent ion-dipole interactions which lower chain mobility. The common limiting T_g value for the three DEG-SA samples at an Mg²⁺/COO^- ratio of ca. 0.5 approaches T_g,, which is the corresponding T_g of a polymer of infinite molar mass.     

Simultaneous sulfide and acetate oxidation under denitrifying conditions using an inverse fluidized bed reactor

BACKGROUND: Simultaneous removal of sulfur, nitrogen and carbon compounds from wastewaters is a commercially important biological process. The objective was to evaluate the influence of the CH₃COO^?/NO₃^? molar ratio on the sulfide oxidation process using an inverse fluidized bed reactor (IFBR). RESULTS: Three molar ratios of CH₃COO^?/NO₃^? (0.85, 0.72 and 0.62) with a constant S^2?/NO₃^? molar ratio of 0.13 were evaluated. At a CH₃COO^?/NO₃^? molar ratio of 0.85, the nitrate, acetate and sulfide removal efficiencies were approximately 100%. The N₂ yield (g N₂ g^?1 NO₃^?‐N consumed) was 0.81. Acetate was mineralized, resulting in a yield of 0.65 g inorganic‐C g^?1 CH₃COO^?‐C consumed. Sulfide was partially oxidized to S⁰, and 71% of the S^2? consumed was recovered as elemental sulfur by a settler installed in the IFBR. At a CH₃COO^?/NO₃^? molar ratio of 0.72, the efficiencies of nitrate, acetate and sulfide consumption were of 100%, with N₂ and inorganic‐C yields of 0.84 and 0.69, respectively. The sulfide was recovered as sulfate instead of S⁰, with a yield of 0.92 g SO₄^2?‐S g^?1 S^2? consumed. CONCLUSIONS: The CH₃COO^?/NO₃^? molar ratio was shown to be an important parameter that can be used to control the fate of sulfide oxidation to either S⁰ or sulfate. In this study, the potential of denitrification for the simultaneous removal of organic matter, sulfide and nitrate from wastewaters was demonstrated, obtaining CO₂, S⁰ and N₂ as the major end products. Copyright © 2008 Society of Chemical Industry     

Preparation of Benzylamine by Highly Selective Reductive Amination of Benzaldehyde Over Ru on an Acidic Activated Carbon Support as the Catalyst

Platinum particles (<1.5 nm) have been shown to behave as bases in their interaction with -alumina. FTIR spectra of adsorbed pyridine probe molecules showed that the acid strength of the -alumina was decreased by the presence of (<1.5 nm) Pt particles. Ammonium chloride treatment converts the primary Pt clusters to H _x Pt _y Cl _z intermediates that de-anchor from the support. Consequently, agglomeration to 8 nm Pt particles was observed following treatment in hydrogen at a relatively mild temperature. For the treated catalyst the IR data of absorbed pyridine show a 3 cm^-1 increase relative to the original Pt/-Al₂O₃ catalyst, indicating a strengthening of the acidity. Changes in the Pt particle size were confirmed by FTIR spectroscopy of CO absorbed onto the Pt particles before and after treatment. Consecutive CO and pyridine probe adsorption demonstrated the electronic interplay between the Pt particles and the support. Pyridine adsorption onto the -alumina support of a Pt/Al₂O₃ catalyst pre-dosed with CO produces a nearly 40 cm^-1 lowering of the CO peak position, indicative of CO bond weakening. In the case of CO adsorbed onto a catalyst pre-dosed with pyridine, a shift in the pyridine IR spectrum was only observed from the original highly dispersed catalyst.     

Influence of anionic form on thermal degradation of TMAHP–cellulose

Trimethylammoniumhydroxypropyl (TMAHP)–cellulose in 10 anionic forms (F^?, Cl^?, Br^?, I^?, HSO, NO, OH^?, HCO, H₂PO, CH₃COO^?) was prepared, and the influence of each anion on thermal degradation in inert atmosphere was studied. With the help of dynamic and isothermal thermogravimetry (TG) it was found that H₂PO ions had the greatest retarding effect on TMAHP–cellulose degradation. From the values of rate constants it can be seen that all ionic forms of TMAHP–cellulose have the starting rate of thermal degradation greater than unmodified cellulose. The calculated values of activation energy of thermal degradation for different ionic forms are decreasing in following sequence: H₂PO > F^? > NO > I^? > Br^? > HCO > Cl^? > HSO > OH^? > unmodified cellulose > CH₃COO^?. From the results of pyrolyse measurements in combination with gas chromatography and mass spectrometry (Py–GC–MS) it follows that the products of the elimination of quarternary ammonium salts are trimethylamine, 3-hydroxy-2-propanone, and, in the case of OH^? form, water. In all other ionic forms the third product is the corresponding acid.     

Influence of different anions on the behaviour of aluminium in aqueous solutions

The influence of chloride, sulfate and perchlorate anions on the behaviour of native oxide layers on aluminium is investigated using electrochemical techniques. Due to its influence on the open circuit potential and the cathodic side of the polarization curve the oxygen concentration has been carefully controlled. Two kinds of attack on a commercially pure aluminium (99.5 wt %) have been observed. In all the investigated 0.5 M Cl^–, 0.5 M ClO^– ₄ and 0.5 M SO^2– ₄ aqueous solutions the metal is corroded around the iron and silicon containing precipitates, but only in Cl^– and ClO^– ₄ solutions is crystallographic pitting observed. Comparison with high purity aluminium (99.99 wt %) shows that pitting corrosion is not influenced by the presence of impurities in the aluminium alloys, but by the presence of anions in solution. The pH and/or oxygen concentration determine whether or not the pitting potential coincides with the corrosion potential.     

Syntheses and Structural Analytical Studies of Two Co(II) Complexes Based on 1,4-Di(benzimidazole-1-yl)benzene

Two new Co(II) complexes of 1,4-di(benzimidazole-1-yl)benzene ligand (L) with the formulas [(CoLCl₂)(CHCl₃)(DMF)]_∞ (1) and [CoL(NO₃)₂]_∞ (2) have been synthesized by anion-directed self-assembly. Both complexes have been characterized by elemental analyses, IR, and X-ray single crystal diffraction. Complexes 1 and 2 exhibit 1D chain structures. In 1, Co(II) ions possess a distorted tetrahedral coordination environment composed of N₂Cl₂ donors from two L ligands and two chloride ions, while the Co(II) ions in 2 reveal a distorted octahedral structure defined by the N₂O₄ donors from two L ligands and two nitrate anions. These results illustrate that the anions play an important role in the self-assembly of metal–organic materials.     

Effect of some anions of some nickel salts on the aqueous polymerization of methyl methacrylate

The aqueous polymerization of methyl methacrylate in the absence and in the presence of some anions of nickel salts was carried out at temperatures of 40°C, 50°C, and 60°C using sodium bisulfite as initiator. The nitrate anion (NO) was found to have the highest catalytic effect and resulted in polymers having the least average molecular weights, while the sulfate anion (SO) was found to have the least catalytic effect and resulted in polymers having the highest average molecular weights. The apparent activation energy for the polymerization process was found to be 4.3, 3.6, 3.8, and 4.8 × 10⁴ J/mol in the absence and in the presence of Ni(NO₃)₂, NiCl₂, and NiSO₄ containing the same amount of nickel (0.00587 g). ¹³C-NMR spectra for the polymers obtained in the absence and in the presence of different nickel anions were found to result in nearly the same tacticity.     

Liquid crystal copolyethers with mixed mesogenic units and flexible spacers

Summary Liquid crystalline copolyethers were prepared from monomer pairs selected from biphenol (BP), dihydroxy--methylstilbene (DHMS), and 2,2-dimethyl-4,4-dihydroxyazoxybenzene (DMAz) which were copolymerized with either dibromononane or dibromodecane spacers by phase transfer catalysis. Nematic LC mesophases were observed for most copolymers, but some exhibited dual mesophases. Smectic to nematic transitions were found in polymers with intermediate ratios of DMAz and DHMS with the nonamethylene spacer. These polymers showed excellent solubility in THF and CHCl₃. The longest mesophase range which consisted of two mesophases was found in a polymer composed of a 4:1 ratio of DHMS to BP and a nonane spacer.     

Aluminium alloys in sulphuric acid Part I: Electrochemical behaviour of rotating and stationary disc electrodes

Anodic oxidation of various aluminium alloys was investigated by means of rotating disc electrodes in 3 M H₂SO₄ as a function of Cl^–, F^–, Zn²⁺ and In³⁺ concentration. Al-In, Al-Zn/In and Al-Zn/Sn alloys yielded current-potential curves at the lowest overpotentials and faradaic efficiencies for anodic oxidation of up to 98% at currents 50 mA cm^–2. While these alloys were electrochemically active in the presence of chloride as the only additive in sulphuric acid, binary aluminium alloys with Ce, Ga, La, Nd, Sn, Ta, Te, Ti or Tl were only active when Cl^–, Zn²⁺ and In³⁺ species were added to the electrolyte. With the exception of Al-Ga, binary alloys displayed high faradaic efficiencies of up to 95%. Fluoride additives resulted in current-potential curves at even more negative potentials than those with chlorides. In contrast to Cl^–, fluoride ions are consumed during the aluminium oxidation process due to complexation with Al(III).     

Theoretical and experimental studies of the pitting of type 316L stainless steel in borate buffer solution containing nitrate ion

Passivity breakdown on Type 316L stainless steel (UNS S31603) in the presence of aggressive (Cl⁻) and inhibitive (NO₃⁻) species has been studied and the experimental data are interpreted in terms of the Point Defect Model (PDM). Combining the PDM with competitive adsorption of Cl⁻ and NO₃⁻ into surface oxygen vacancies at the passive film/solution interface predicts that the critical breakdown potential (V_c) will vary linearly with log[Cl⁻] or log([Cl⁻]/[NO₃⁻]) for systems containing only chloride ion or chloride plus nitrate ion, respectively. The experimental measurements confirm these linear relationships and fundamental parameters contained within the PDM have been determined. The transfer coefficient, α₀, of the reaction in which a cation is ejected from the barrier layer to form the surface vacancy pair, , is about 1.00, indicating that the transition state resembles the products. Furthermore, the dependence of V_c on potential scan rate has been measured, and the critical, areal concentration of condensed cation vacancies (ζ) at the metal/barrier layer interface been calculated. That value is in good agreement with the theoretical value calculated from the structure of Cr₂O₃, of which the barrier layer is postulated to comprise, demonstrating that the PDM successfully accounts for passivity breakdown on UNS S31603 in aqueous solutions containing both aggressive and inhibitive species.