Molybdenum nitride for the direct decomposition of NO

The physico-chemical properties of passivated -Mo₂N have been investigated. The material showed high activities for NO direct decomposition: nearly 100% NO conversion and 95% N₂ selectivity were achieved at 450C. The amount of O₂ taken up by -Mo₂N increased with temperature rise and reached 3133.9 molg^–1 at 450C; we conclude that there formation of Mo₂O_xN_y occurred. This oxygen-saturated -Mo₂N material was catalytically active: NO conversion and N₂ selectivity were 89 and 92% at 450C. We found that by means of H₂ reduction at 450C, Mo₂O_xN_y could be reduced back to -Mo₂N and the oxidation/reduction cycle is repeatable; such a behaviour and the high oxygen capacity (3133.9 molg^–1) of -Mo₂N suggest that -Mo₂N is a promising catalytic material for automobile exhaust purification.     

Heterogeneous asymmetric reactions. 23. Enantioselective hydrogenation of ethyl pyruvate over cinchonine- and α-isocinchonine-modified platinum catalysts

The enantioselective hydrogenation of ethyl pyruvate to (S)-ethyl lactate over cinchonine- and -isocinchonine-modified Pt/Al₂O₃ catalysts was studied as a function of modifier concentration and reaction temperature. The maximum enantioselectivities obtained under the applied mild conditions were 89% ee using cinchonine (0.014 mmoldm^–3, 1 bar H₂, 23°C, 6% AcOH in toluene), and 76% ee in the case of -isocinchonine (0.14 mmoldm^–3, 1 bar H₂, –10°C, 6% AcOH in toluene). Since -isocinchonine of rigid structure exists only in anti-open conformation these data provide additional experimental evidence to support the former suggestion concerning the dominating role of anti-open conformation in these cinchona-modified enantioselective hydrogenations.     

Synthesis, Characterization and Optimum Reaction Conditions of Oligo-N, N′-bis (2-hydroxy-1-naphthalidene) Thiosemicarbazone

The oxidative polycondenzation reaction conditions of N, N-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone (HNTSC) using air oxygen, H₂O₂ and NaOCl were studied in an aqueous alkaline medium between 50–90°C. Oligo-N, N-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone was characterized by ¹H-NMR, FT-IR, UV-Vis, size exclusion chromatography (SEC) and elemental analysis techniques. Solubility testing of oligomer was investigated using organic solvents such as DMF, THF, DMSO, methanol, ethanol, CHCl₃, CCl₄, toluene acetonitrile, ethyl acetate, concentrated H₂SO₄ and an aqueous alkaline solution. Using NaOCl, H₂O₂ and air O₂ oxidants, conversion to oligo-N, N-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone (OHNTSC) of N, N-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone was found to be 85, 80 and 76%, respectively, in an aqueous alkaline medium. According to the SEC analyses, the number-average molecular weight, weight-average molecular weight and polydispersity index values of OHNTSC synthesized were found to be 1050 gmol^–1 1715 gmol^–1 and 1.63, using NaOCl, and 2137, 2957 gmol^–1 and 1.38, using air O₂ and 2155 gmol^–1 4164 gmol^–1 and 1.93, using air H₂O₂, respectively. Also, TG analysis was shown to be unstable of oligo-N, N-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone against thermo-oxidative decomposition. The weight loss of OHNTSC was found to be 97.29% at 900°C.     

Active-oxygen species on non-reducible rare-earth-oxide-based catalysts in oxidative coupling of methane

From supplementary in situ Raman spectroscopic studies of active-oxygen species on non-reducible rare-earth-oxide-based catalysts in the oxidative coupling of methane (OCM) and structural adaptability considerations, further support has been obtained for our proposal that there may be an active and elusive precursor (of O₂ ^– and O₂ ^2– adspecies), most probably O₃ ^2– formed from reversible redox coupling of an O₂ adspecies at an anionic vacancy with a neighboring O^2– in the surface lattice. This active precursor may initiate H abstraction from CH₄ and be itself converted to OH^–+O₂ ^–, or it may abstract an electron from the oxide lattice and be converted to O₂ ^2–+O^–. The prospect of developing this type of OCM catalysts is discussed.     

Thermally stable alumina–gallia aerogel as a catalyst for NO reduction with C3H6 in the presence of excess oxygen

In order to improve thermal stability, an alumina–gallia aerogel was prepared and the catalyst performance for NO reduction with C₃H₆ was compared with that of an alumina–gallia xerogel. Basically, both were prepared by a sol–gel method with supercritical drying for the former, while with oven drying for the latter. Upon heating at 800, 900, and 1000°C, the aerogel exhibited higher NO conversion than the xerogel at reaction temperature <400°C, while NO conversion was lower on the former than on the latter at >500°C. At 450°C, NO conversion was almost the same for these two catalysts. A marked difference was observed upon heating them at 1100°C: the aerogel still maintained quite a high activity, while the xerogel greatly lost it. After heating the aerogel at 1100°C, -phase alumina remained untransformed with its surface area of 80 m²/g, while the xerogel was completely transformed to -alumina with its surface area of 6 m²/g. The high activity remaining on the aerogel heated at 1100°C was ascribed to its large surface area.     

Improvement of Catalytic Performance in Isobutane Oxidation to Methacrylic Acid of Keggin-Type Phosphomolybdates by Preparation via Lacunary Precursors: Nature of the Active Sites

A solvent-free method of preparation of a vanadium(V) phosphate is described and discussed. Reaction of V₂O₅ with H₃PO₄ in the absence of water at 150°C leads to the formation of a new catalytic material that is designated as anhydrous VOPO₄. The material readily hydrates to form VOPO₄2H₂O and has been characterised using powder X-ray diffraction, in situ Raman spectroscopy and ³¹P MAS NMR spectrometry. On activation in dry N₂ followed by reaction with butane/air another novel material is formed that has an intrinsic activity for maleic anhydride that is similar to catalysts derived from VOHPO₄0.5H₂O under comparable conditions. Activation of VOPO₄2H₂O under comparable conditions leads to the formation of _I-VOPO₄ which exhibits no partial oxidation activity. Reaction of anhydrous VOPO₄ with alcohols leads to the exclusive formation of VO(H₂PO₄)₂ in further contrast to VOPO₄2H₂O which under similar conditions leads to the synthesis of VOHPO₄0.5H₂O.     

Sulphidation of an oxidic CoMo/Al2O3 catalyst under practical conditions: different kinds of sulphur species

The sulphidation of a CoMo/Al₂O₃ hydrotreating catalyst was studied under pressure and flow conditions close to industrial practice. The sulphiding mixture contained equal amounts of H₂S and CH₄ diluted in hydrogen under 3.9 MPa total pressure. The oxidic precursor was flushed by the reagent gas at 40°C for 10 h, then the temperature was raised to 400°C within 2 h. Mass variation was continuously recorded by means of a suspension magnetic balance, and the gas phase was analysed by mass spectrometry. Sulphur contents were also determined at intermediate temperatures by chemical analyses. Thus, mass variations due to the presence of adsorbed species or to the formation of CoMo sulphides could be distinguished. The rapid gain in mass noted at 40°C was mostly due to adsorption of H₂S over the oxidic solid, since it increased with H₂S partial pressure. At this stage, however, a small amount of the reactive oxygen was already exchanged for sulphur. Upon raising the temperature, the mass decreased due to a combination of desorption and sulphiding steps. Above 140°C, H₂S consumption was evidenced, together with water production, and the rate of sulphiding increased with the H₂S partial pressure. At 300°C, the mass variation was close to that expected for complete transformation into Co₉S₈ and MoS₂. Above 350°C, the mass further increased due to the replacement of adsorbed water by H₂S. At 400°C, an important excess mass was observed at all H₂S partial pressures. Thus, the adsorption sites on the metal sulphides are essentially saturated by H₂S species under practical conditions.     

Lean NOx catalysis over alumina‐supported catalysts

aluminasupported catalysts show promise as lean NO_x catalysts. The role of alumina in influencing the structural and chemical properties of the active phase supported on it is discussed using some effective aluminabased lean NO_x catalysts. These include Ag/Al₂O₃, CoO_x/Al₂O₃ and SnO₂/Al₂O₃. Alumina plays an important role in stabilizing Ag in the oxidic phase and cobalt in the 2+ oxidation state. For SnO₂/Al₂O₃, alumina increases the SnO₂ surface area. On both Ag/Al₂O₃ and SnO₂/Al₂O₃, alumina also participates actively in the NO_x reduction reaction. An active organic intermediate is formed on Ag or Sn oxide which reacts with NO_x subsequently on alumina to form N₂.     

Mechanisms of Iron Activation on Fe-Containing Zeolites and the Charge of α-Oxygen

According to previous Mössbauer data [1] -sites formation at the activation of Fe-containing zeolites is accompanied by irreversible self-reduction of the iron, proceeding without participation of an external reducing agent. Reduced Fe²⁺ ions are inert to O₂ but are reversibly oxidized to Fe³⁺ by N₂O, generating the -oxygen species, O, which provide selective oxidation of hydrocarbons.In this work, the mechanism of -sites formation was studied via quantitative measurement of the dioxygen amount desorbed into the gas phase at the step of self-reduction. A prominent role of the zeolite matrix chemical composition has been revealed. For example, with zeolites of Al–Si composition (FeZSM-5 and Fe-), heating to 900 °C in a closed vacuum space leads to irreversible evolution of O₂, which is accompanied by the immediate formation of -sites. Similar heating of B–Si and Ti–Si zeolites also leads to dioxygen evolution; however, this evolution is reversible and is not accompanied by formation of -sites. Activation of these zeolites occurs only in the presence of water vapor. Stoichiometric measurements showed that in terms of charge one regular O^2- ion, removed at the activation, is equivalent to two -oxygen atoms. So, -oxygen is identified as an ion-radical species O ^-., whose unique oxidation properties still distinguish it from the generally observed O^-. radicals.The mechanism of -sites formation is proposed, in which the process of strong chemical stabilization of reduced Fe²⁺ atoms in the zeolite structure is a key step, making impossible the reoxidation of the iron with O₂.     

Electrosynthesis of 4,4′-dinitroazobenzene on PbO2 electrodes

Parameters which affect the electrosynthesis of 4,4-dinitroazobenzene from p-nitroaniline on platinum and PbO₂ electrodes were investigated and optimum conditions were determined. Maximum conversion efficiency for electrosynthesis was 95% with a pure -PbO₂ electrode. It was found that the electrocatalytic activity of a PbO₂ electrode depends upon its / ratio and its degree of crystallinity. The effects of the added base and water on the conversion efficiency were also elucidated.     

Characterization of phosphorus availability in selected New Zealand grassland soils

Appropriate evaluation of phosphorus (P) availability in soil is aprerequisite for ensuring the productivity and long-term sustainable managementof agroecosystems. Fifteen soils presently under grassland were collected fromdifferent areas of New Zealand and soil P availability was assessed by isotopicexchange kinetics (IEK) and related to P forms obtained by chemicalfractionation (sequential extraction). Concentrations of total P determined inthe 15 soils ranged from 375 to 2607 mg kg^–1(mean1104 mg kg^–1). Mean concentrations of inorganic P(Pi) extracted by sequential extraction with ammonium chloride, sodiumbicarbonate, sodium hydroxide (first), hydrochloric acid and sodium hydroxide(second) were 1.2, 41, 205, 113 and 23 mg kg^–1,respectively. Mean concentrations of organic P (Po) extracted by sodiumbicarbonate, sodium hydroxide (first) and sodium hydroxide (second) were 133,417 and 105 mg kg^–1, respectively. Similarly,results from IEK analysis showed that the intensity (water soluble Pi (Cp)),capacity (R/r₁ and n), and quantity (E value,isotopically exchangeable P pools (E_{1 min},E_{1 min–24 h},E_{24 h–3 m},E_{>3 m})) factors varied markedlyamongst soils. Thus Cp concentrations ranged from 0.02–1.90 mgL^–1, while concentrations of Pi determined in theE_{1 min}, E_{1 min–24},E_{24 h–3 m},E_{>3 m} pools were 2–29 (mean 10), 10–321(76), 11–745 (152), and 8–498 (177) mgkg^–1, respectively. The corresponding values forR/r₁ and n were 1.0–17.7 (mean 4.5) and0.10–0.50 (mean 0.37), respectively. Regression analysis revealed that Cpconcentrations were exponentially and inversely proportional toR/r₁,n and P sorption index (PSI)(R²=0.806(P<0.01), 0.852 (P<0.01) and 0.660(P<0.01), respectively). Cluster analysis identified twobroad groups of soils, namely those with low P availability (mean Cp0.11 mg L^–1, E_{1 min} Pi 5mg kg^–1, R/r₁ 3.9,n 0.44), and those with high P availability (mean Cp 1.33mg L^–1, E_{1 min} Pi 20mg kg^–1, R/r₁ 1.21,n 0.16). Correlation analysis indicated thatE_{1 min} P i was significantly correlated with bicarbonateextractable Pi (BPi, R²=0.37,P<0.05) and thesum of ammonium chloride extractable Pi (APi) and BPi(R²=0.38,P<0.05). However, the concentration of Pi in theE_{1 min} pool was generally lower than the sum of APi andBPi. Sodium hydroxide extractable Pi (N₁Pi) was significantlycorrelated with the sum of the E_{1 min},E_{1 min–24 h},E_{24 h–3 m} Pi pools(R₂=0.974, P<0.01),indicating that N₁Pi fractioncould be considered as representing potentially available soil P for pasturespecies over a growing season.     

Synthesis of ternary Li–Mn–O phase at a temperature of 260 ∘C and electrochemical lithium insertion into the oxide

A lithium–manganese oxide, Li _x MnO₂ (x=0.30.6), has been synthesized by heating a mixture (Li/Mn ratio=0.30.8) of electrolytic manganese dioxide (EMD) and LiNO₃ in air at moderate temperature, 260 C. The formation of the Li–Mn–O phase was confirmed by X-ray diffraction, atomic absorption and electrochemical measurements. Electrochemical properties of the Li–Mn–O were examined in LiClO₄-propylene carbonate electrolyte solution. About 0.3 Li in Li _x MnO₂ (x=0.30.6) was removed on initial charging, resulting in characteristic two discharge plateaus around 3.5V and 2.8V vs Li/Li⁺. The Li _x MnO₂ synthesized by heating at Li/Mn ratio=0.5 demonstrated higher discharge capacity, about 250mAh (g of oxide)^–1 initially, and better cyclability as a positive electrode for lithium secondary battery use as compared to EMD.     

Steam reforming of n-butane on Pd/ceria

We have examined the steam reforming of n-butane on ceria, 1 wt% Pd/ceria, 1 wt% Pd/alumina, and 15 wt% Ni/silica between 573 and 873 K, with H₂O:C ratios between 1.0 and 2.0. No stable rates could be observed on Ni/silica due to rapid coking under these conditions. While rates were stable on the other catalysts, Pd/ceria showed a much higher activity than either Pd/alumina or ceria individually. Of additional interest, CO₂:CO ratios were much higher on Pd/ceria and approached equilibrium. The reaction order for n-butane on Pd/ceria was 0.15. For H₂O, reaction order changed from 0.6 to zero at the stoichiometric, n-butane:H₂O ratio. It is suggested that the high activity of Pd/ceria for this reaction is due to a dual-function mechanism, in which ceria can be oxidized by H₂O and then supply oxygen to the Pd.     

Origin of rate bistability in Mn–O/Al2O3 catalysts for carbon monoxide oxidation: role of the Jahn–Teller effect

Peculiarities in catalytic activity in carbon monoxide oxidation as well as some structure, electronic and magnetic properties of the three oxide catalysts, Mn³⁺–O/Al₂O₃ (1), Mn³⁺–O–Fe/Al₂O₃ (Mn-substituted spinel, 2) and -Fe₂O₃/Al₂O₃ (3), were studied by kinetic measurements and by Mössbauer spectroscopy. The catalysts 1 and 2 showed a kinetic bistability with a sharp transition towards more reactive state at 200°C (ignition point). In contrast, for catalyst 3, at 200–250°C, the behavior of reaction rate against temperature did not display noticeable hysteresis. On cooling the catalysts 1 and 2, extinction was observed at about 170 and 120°C, respectively, i.e., at 30–80°C lower than the corresponding ignition points. Proximity of activation energy for the high and low activity (15–19 kJ/mol) for both Mn-containing catalysts suggests an increase in the number of active sites at high temperature with no changes in the reaction mechanism. The considerable difference between Mn-containing catalysts 1, 2 and Fe-containing catalyst 3 may be caused by Jahn–Teller (JT) type distortions of the oxygen polyhedron around Mn³⁺. A significant spontaneous axial bond stretching within the local polyhedron seems to diminish Mn–O binding energy, facilitate the participation of surface oxygen species, O_S, in the oxidation of CO by a redox mechanism and promote oxygen vacancies at the surface that would cause considerable effect on the activity. An increase in the width of the counterclockwise hysteresis loop for the catalyst 2 compared to the catalyst 1 indicates that clusters of mixed spinel provide more active sites and more labile O_S species than clusters of the binary Mn oxide.     

A study of the acidic and catalytic properties of pure and sulfated zirconia–titania and zirconia–silica mixed oxides

Protonated pyridine (PyH⁺) was not found on ZrO₂ (Z) or ZrO₂–TiO₂ (ZT), but was detected on sulfated oxides (ZS, ZTS) by IR spectroscopy. In contrast, ZrO₂–SiO₂ samples containing about 30–80 mol% ZrO₂ showed Brønsted acidity both in nonsulfated (ZS) and sulfated (ZSS) forms. The total acidity was determined by NH₃TPD. Introduction of sulfate ions increased the sitespecific catalytic activity (TOF) in the conversion of cyclopropane or nhexane. The effect of sulfate ions was more significant on samples rich in zirconia. Results suggest that Zr is homogeneously distributed in ZS samples rich in silica. Zirconiabound dimeric sulfate, generating strong acidity, could not be formed in these preparations due to the absence of fairly large ZrO₂ domains.     

Synthesis and Redox Properties of a π-Conjugated Cyclobutadienecobalt Polymer Containing Ferrocenyl Groups

The reaction of CpCo(PPh₃)₂, in which Cp= ⁵-cyclopentadienyl, with a -conjugated diacetylene, FcCC–o-C₆H₄–CCFc, in which Fc=ferrocenyl, was found to give a cyclobutadienecobalt mononuclear complex, { ⁴-C₄Fc₂(o-FcC₆H₄)₂}CoCp (1), the crystal structure of which was determined by X-ray crystallography. In contrast, the reaction of CpCo(PPh₃)₂ with FcCC–p-C₆H₄–CCFc affords a cyclobutadienecobalt polymer, [p-C₆H₄( ⁴-C₄Fc₂)CoCp] _n (2). The monocobalt complex 1 shows reversible 1e^– and 3e^– redox waves at E ⁰=0.116 and 0.350 V vs Ag/Ag⁺, and the polymer complex 2 shows two chemically reversible redox waves at E ⁰=0.143 and 0.219 V for the oxidation of the ferrocenyl moieties in the cyclic voltammogram. Crystal data are as follows: (1, C₆₅H₄₉CoFe₄), triclinic, space group P\={1} (No. 2), a=13.547(4), b=16.197(4), c=11.763(4) Å, =106.79(2), =97.93(3), =97.12(3), V=2410(1) ų, Z=2.     

A Sol–Gel Derived CuOx/Al2O3–ZrO2 Catalyst for the Selective Reduction of NO by Propane in the Presence of Excess Oxygen

Copper catalysts supported on alumina-doped zirconia were prepared by sol–gel processing followed by supercritical drying or aging in the mother solution at 100°C. After drying and calcination, the catalyst supports were impregnated with a copper(II) nitrate aqueous solution by the incipient wetness method to achieve a Cu loading of about 2%. The samples showed 90% NO conversion at 350–400°C. The catalytic performance of these systems appears to be determined by the degree of clustering of copper cations as probed by FTIR spectroscopy of adsorbed CO.     

Phase transitions and dimensional and morphological changes in an “Aluminum Hydroxide-Alumina” system under a shock-wave action

A method is proposed to study the sequence of phase transitions in powdered materials under a shock-wave action. It is shown that the aluminum hydroxide-alumina system has the following sequence of phase transformations under a shock-wave action: bayerite boehmite -Al₂O₃ -Al₂O₃. It is found that there are no transitional high-temperature modifications of alumina. A method is developed for obtaining a submicron alumina powder, which allows obtaining materials with a controlled phase composition, including a thermodynamically stable -modification of Al₂O₃. The specific features of the morphological structure and the phase and structural characteristics of powders after a shock-wave action are considered.Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 1, pp. 110–119, January–February, 2005.     

Continuous oxidation of benzyl alcohol in “supercritical” carbon dioxide

Supercritical (dense) carbon dioxide has been applied as solvent for the partial oxidation of benzyl alcohol with molecular oxygen in a fixed-bed reactor. High rate and good selectivity to benzaldehyde (93–97%) has been achieved with 0.5 wt% Pd/alumina or 0.5 wt% Pd/C, at around 100C and 100 bar, using only moderate excess of oxygen. The by-product benzoic acid has an autocatalytic effect on the hydration of benzaldehyde, and the subsequent oxidative dehydrogenation leads to benzoic acid, and benzyl benzoate by esterification. Promotion of Pd by Pb improves the selectivity. No catalyst deactivation or metal leaching has been observed. The method provides reasonable yields at much lower temperature than that applied in conventional gas phase oxidation, showing a potential for the synthesis of thermolabile, water-insoluble aromatic aldehydes.     

Kinetics and Mechanism of Copolymerization of α-terpineol with Methylmethacrylate in Presence of Azobisisobutyronitrile as an Initiator

The radical copolymerization of -terpineol with methyl-methacrylate in xylene at 80±0.1C for 50 minutes in the presence of azobisisobutyronitrile (AIBN) follows ideal kinetics and results in the formation of a functional and random copolymer. The activation energy is 33 KJ/mole. The IR spectrum and NMR spectra of the copolymer(s) shows the bands at 1750 and 3400 cm^–1 for ester group of methylmethacrylate and alcoholic group of -terpineol and peaks at 3 to 4 for methoxy group and at 6.5 to 7.5 due to alcoholic group of methylmethacrylate and -terpineol repectively. The values of reactivity ratios, calculated by Kelen–Tüdos method, are r ₁ (MMA) = 0.18 and r ₂ (-terpineol) = 0.046. The Alfrey-Price; Q–e parameters for -terpineol has been calculated as 0.149 and 2.486. The mechanism of copolymerization has been elucidated and it is concluded that the double bond present in the monocyclic ring of -terpineol is an active site for copolymerization and the alcoholic group of -terpineol remain to give functional copolymer.