Catalytic Methoxycarbonylation of Aromatic Diamines with Dimethyl Carbonate to Their Dicarbamates Using Zinc Acetate

The methoxycarbonylation of 2,4-toluene diamine and 4,4-diphenylmethane diamine with dimethyl carbonate to the corresponding dicarbamates using zinc acetate was carried out at 453 K. Zn(OAc)₂, prepared by evacuating Zn(OAc)₂2H₂O at 383 K for 2 h, yields dimethyltoluene-2,4-dicarbamate in 96% yield in 2 h, while Zn(OAc)₂2H₂O yields dimethyl-4,4-methylenediphenyldicarbamate in 98% yield at 453 K in 2 h.The structure of methyl 3-amino-4-methyl phenyl carbamate, which is one of the intermediates for the reaction of 2,4-toluene diamine with dimethyl carbonate into dimethyltoluene-2,4-dicarbamate, has been determined by measuring the NOE spectrum of ¹H NMR.     

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.     

Study of the Supported K2MoO4 Catalyst for Methanethiol Synthesis by One Step from High H2S-Containing Syngas

ESR and XPS are used to study the Mo-based catalysts MoO₃/K₂CO₃/SiO₂ and K₂MoO₄/SiO₂ prepared with two kinds of precursors, (NH₄)₆Mo₇O₂₄4H₂O and K₂MoO₄. The catalytic properties of the catalysts for methanethiol synthesis from high H₂S-containing syngas are explored. The activity assay shows that the two catalysts have much the same activity for the reaction. By the ESR characterization of both functioning catalysts, the resonant signals of oxo-Mo(V) (g=1.93), thio-Mo(V) (g=1.98) and S (g=2.01 or 2.04) can be detected. In the catalyst MoO₃/SiO₂ modified with K₂CO₃, as increasing amounts of K₂CO₃ are added, the content of oxo-Mo(V) increases, but thio-Mo(V) decreases. The XPS characterization indicates that Mo has mixed valence states of Mo⁴⁺, Mo⁵⁺ and Mo⁶⁺, and that S includes three kinds of species: S^2– (161.5 eV), [S–S]^2– (162.5 eV) and S⁶⁺ (168.5 eV). Adding K₂CO₃ promoter to the catalysts, the Mo species of high valence state is easily sulphided and reduced to Mo₂S and oxo-M(V), and the derivation of [S–S]^2– and S^2– species from S is promoted simultaneously. The methanethiol synthesis is favored if the mole ratio of (Mo⁶⁺ + Mo⁵⁺)/Mo⁴⁺ 0.8 and S^2–/[S–S]^2– is kept at a value of about 1.     

Some Factors Influencing the Morphology of α-Zirconium Phosphate and its Intercalation Reactions with a Bifunctional Thioether Amine

Crystalline samples of -zirconium phosphate, (-ZrP, -Zr(HPO₄)₂·H₂O) have been prepared by decomposition of zirconium fluoride complexes in the presence of phosphoric acid under a variety of conditions. The crystallinity and morphology have been shown to depend on a number of factors including the F^–/Zr⁴⁺ ratio, the concentration of Zr⁴⁺ ions, the material of the reaction vessel and the reaction temperature. Under conditions of rapid precipitation small plate-like crystals of -ZrP are produced whereas under conditions of slow crystallisation larger crystals with a lower aspect ratio are formed. The relative intensities of the d ₀₀₂, d ₁₁₀ and d ₁₁₂ reflections observed by X-ray powder diffraction show a correlation with the crystal morphology as determined by SEM.The intercalation reaction of 4-(methylmercapto)aniline with different samples of -ZrP under a variety of conditions has been studied. Incomplete intercalation is observed in each case, with the extent of intercalation depending on both the morphology of the -ZrP and the reaction conditions. The intercalated amine has been shown to exist as a mixture of protonated cations and neutral molecules.     

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.     

The Preferential Oxidation of CO: Selective Combinatorial Activity and Infrared Studies

From EXAFS (extended X-ray absorption fine structure) analysis, gold was found to have mainly oxygen in its nearest coordination shell in the fresh Au/-Al₂O₃ catalyst prepared by AuCl₃ impregnation and vacuum drying at room temperature. After thermal treatment under helium, chlorine appeared within the nearest neighbors of gold and more chlorine showed up as the treatment temperature was increased from 323 to 473K. No reduced Au species was observed up to 473K under He. However, the gold became reduced during CO oxidation at 373K and above. The precursor AuCl₃ was found to deposit on -Al₂O₃ via bonding to surface hydroxyl groups. This catalyst showed nearly 100% CO conversion at 573K, but a very low activity at 373 K under the conditions used in this study. Neither the residual chlorine nor the extent of reduction can explain the low activity at lower temperatures.     

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.     

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.     

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.     

Both Ovarian Fluid and Female Urine Increase Sex Steroid Hormone Levels in Mature Atlantic Salmon (Salmo salar) Male Parr

We compared the ability of urine and ovarian fluid from female Atlantic salmon (Salmo salar) to stimulate increase in plasma concentrations of sex steroid hormones in mature conspecific male parr (priming effect of the stimuli). We also tested the hypothesis that prostaglandin F₂ (PGF₂) may act as a priming pheromone in the tested stimulants. Individual males of salmon parr were exposed to female urine, ovarian fluid, urine–ovarian fluid mix, or PGF₂. Plasma concentrations of the sex steroids of 17,20-dihydroxy-4-pregnen-3-one (17,20-P) were higher in males exposed to urine, ovarian fluids, and PGF₂ compared to control males. PGF₂ and a mixture of urine and ovarian fluid also gave increased concentrations of 11-ketotestosterone (11-KT). Concentrations of PGF₂ were higher in ovarian fluids than in urine. A behavior test with mature male parr in a fluviarium showed neither attraction to nor avoidance of 0.1 nM PGF₂, but plasma levels of 17,20-P were significantly higher in exposed males compared to controls.     

Preparation and Characterization of Copper Catalysts Supported on Mesoporous Al2O3 Nanofibers for N2O Reduction to N2

The gas-phase hydrogenation of benzene to cyclohexane over Ce_{1 - x} Pt _x O_{2 -} (x = 0.01, 0.02) catalyst was investigated in the temperature range 80-200 °C. A 42% conversion of benzene to cyclohexane with 100% specificity was observed at 100 °C over Ce_0.98Pt_0.02O_{2 -} with a catalyst residence time of 1.22 × 10⁴ g s/mol of benzene. The activity of the catalyst was compared with those of Pt metal, combustion-synthesized Pt/-Al₂O₃ and Pt/-Al₂O₃. The turnover frequency value of Ce_0.98Pt_0.02O_{2 -} is 0.292, which is an order of magnitude higher than those of the other Pt catalysts investigated. The kinetics of reaction and the deactivation behavior of the catalyst were studied and a regeneration methodology was suggested. The deactivation kinetics and structural evidence from XRD, XPS, TGA and H₂ uptake studies suggest that the oxidized Pt in Ce_0.98Pt_0.02O_{2 -} is responsible for the high catalytic activity towards benzene hydrogenation.     

Anisotropic structure analysis for cobalt oxides on α-Al2O3(0001) by polarized total-reflection fluorescence extended X-ray absorption fine structure

Anisotropic structure analyses for [CoO_x]/-Al₂O₃ (0001) and [Co₃O₄]_n /-Al₂O₃ (0001) which were derived from Co₂(CO)₈/-Al₂O₃ (0001) were performed by a polarized total-reflection fluorescence extended X-ray absorption fine structure (EXAFS) technique. Both s- and p-polarized EXAFS data revealed that the cobalt atoms of [CoO_x] were located on three-fold hollow sites of -Al₂O₃ (0001) in a monomer form and that a thin spinel structure [Co₃O₄] grew with the (001) plane parallel to -Al₂O₃ (0001).     

Cobalt‐catalyzed amination of 1,3‐cyclohexanediol and 2,4‐pentanediol in supercritical ammonia

The onestep procedure of amination of bifunctional secondary alcohols to diamines has been investigated in a continuous fixedbed reactor. Application of supercritical NH₃ as a solvent and reactant suppressed catalyst deactivation and improved selectivities to amino alcohol intermediates, whereas selectivities to diamines remained poor (8–10%). The main reason for the low diamine selectivity of 1,3dihydroxy compounds is water elimination leading to undesired monofunctional products via ,unsaturated alcohol, ketone or amine intermediates. This side reaction does not occur with 1,4dihydroxy compounds which afford high aminol and diamine selectivities under similar conditions. Amination of secondary diols with ammonia was found to be faster, but less selective than that of the corresponding primary 1,3propanediol.     

Surface characterization of zirconium titanate (ZrTiO4) powder by measurements of electrical photoconductance and photoassisted oxygen isotope exchange

The photosensitivity of a ZrTiO₄ sample (33 m²/g) prepared by a sol-gel method has been assessed in the presence of O₂ by both photoconductance and oxygen isotope exchange (OIE) measurements at room temperature at wavelengths > 290 nm. For oxygen pressures < ca. 13.3 Pa, the steady-state photoconductance of ZrTiO₄ was unaffected by , which indicated that the direct recombination of the photoproduced charges played the dominant role. At higher pressures, varied as the reciprocal of , which was consistent with the fact that the electronic equilibrium was then governed by O₂ + e^– O ₂ ^– . OIE over ZrTiO₄ occurred predominantly via the overall mechanism which involves the exchange of two surface oxygen atoms for each exchange act. It was very slow as compared with OIE over photocatalytically active anatase samples which, in addition, occurs via another mechanism. These results allow one to predict that this ZrTiO₄ sample is a poorly active photocatalyst for oxidations involving gaseous oxygen, and further illustrate the interest of and OIE measurements to evaluate the photosensitivity of semiconductor oxide samples.     

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.     

From Bifunctional Site to Metal–Proton Adduct Site in Alkane Reforming Reactions on Sulphated-Zirconia-Supported Pt or Pd or Ir Catalysts

Isomerization reactions of n-heptane, n-octane and n-nonane are studied on sulphated-zirconia-supported 0.2 wt% Pt, Pd or Ir catalysts. Evolutions of isomer selectivity versus total conversion and reaction temperatures are analysed. When total conversion (_T) is increased, isomer selectivity (%S _isom) is decreased and the slope of the curve %S _isom=f(_T) is more pronounced when the carbon number in the alkane is more important. At isoconversion, around 20%, below 473 K, cracking is favoured over isomerization reaction, and above 473 K it is the reverse. Moreover, with n-heptane, when the catalytic reaction occurred at 423 K and at low conversion, _T20%, we observed a large decrease in the isomer selectivity percentages on Pd/SZ and Ir/SZ compared to Pt/SZ. What is remarkable is that, at this low temperature, both metals are inactive in the carbon–carbon bond rupture. To explain these results the following points are raised: (i) an associative mechanism is proposed for the adsorption step of the alkane involving an agostic intermediate species where the carbon–hydrogen bonds act as ligands to the transition metal centres forming covalent C–HM systems, and (ii) a metal–proton adduct site, which gathers metallic and acidic sites is suggested. This approach seems to better explain our results than the traditional bifunctional mechanism.     

Coarsening of Mesoporous α-Al2 3 Ceramics

Until recently, the processing of high surface area alumina ceramics has been restricted to transitional phases such as , , and . In this study, a nanocrystalline -Al_{2 3} powder (100 m²/g) was processed into mesoporous -Al_{2 3} ceramics with surface areas in the range 20 to 80 m²/g. Hence, the opportunity exists to study the effect of thermal treatment on the pore structure of a high surface area -Al_{2 3} ceramic in the temperature range 600°C to 1000°C. The reduction in surface area was characterized as pure coarsening by surface diffusion. Examination of the pore structure showed both intraparticle pores and interparticle pores in the temperature range 600°C to 800°C and only interparticle pores above 800°C. The powder particles were dense and polycrystalline. However, much of their internal structure is lost in heat treatments above 1000°C.     

Partial oxidation of methane to synthesis gas

Partial oxidation of methane to synthesis gas has been carried out over a number of transition metal catalysts under a range of conditions. It is found that the metals Ni, Ru, Rh, Pd, Ir and Pt, either supported on alumina or present in mixed metal oxide precursors, will bring the system to equilibrium. The yield of CO and H2 improves with increasing temperature in the range 650–1050 K, and decreases with increasing pressure between 1 and 20 atm. An excellent yield (92%) is obtained with a 421 N₂CH₄O₂ ratio at 1050 K and atmospheric pressure, with a space velocity of 4×10⁴ hour^–1.     

Effect of Dehydration of VOPO4⋅2H2O on the Preparation and Reactivity of Vanadium Phosphate Catalyst for the Oxidation of n-Butane

The effect of drying of VOPO₄2H₂O on the preparation of vanadium phosphate catalysts for the selective oxidation of n-butane to maleic anhydride is described and discussed. It is found that partially dehydrated samples of the dihydrate containing small amounts of _I-VOPO₄ are formed when the material is initially dried. The presence of this impurity leads to a final catalyst containing trace amounts of _I-VOPO₄ in combination with (VO)₂P₂O₇ and this combination leads to a catalyst with a higher activity but with a lower selectivity to maleic anhydride. The drying stage is also found to influence the surface area and intrinsic activity of the activated catalyst.