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.     

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.     

Acid‐catalyzed isobutane–isobutylene alkylation in liquid carbon dioxide solution

Liquid carbon dioxide was studied as a solvent for the isobutane–isobutylene alkylation. The acid catalysts in the reaction were anhydrous HF (AHF), pyridinium–poly(hydrogen fluoride) complex (PPHF), concentrated sulfuric acid and trifluoromethanesulfonic acid (TFSA). The effect of the acid–hydrocarbon volume ratio, temperature and residence time on the alkylate quality were studied over the temperature range of 50 T 0 °C. Carbon dioxide as a competing weak base decreases the acidity of the system which parallels the alkylate quality. In the case of HF and TFSA catalysts, solvent CO₂ increased the octane number of the alkylate product (RON 95.6 for HF and 88.0 for TFSAcatalyzed alkylation with CO₂ solvent).     

Synthesis of HFC-134a over CrF3/AlF3 catalysts

The effect of the structure of AlF₃ supports in CrF₃/AlF₃ catalysts and their activity were studied, and a selection of suitable reaction conditions for fluorination of trichloroethylene and HCFC-133a was made. We found that neither AlF₃ (- and -modifications) nor CrF₃/-AlF₃ exhibits significant activity for the reaction of HF with CCl₂=CHC1 or CF₃CH₂Cl. However, CrF₃/-AlF₃ exhibits high activity, which increases with increasing surface area and decreasing crystallite size of the -AlF₃ support, and that dramatically affects the fiuorination of CF₃CH₂Cl. Investigation of a series of CrF₃/-AlF₃ catalysts shows that the turnover rates per unit of the total surface area and of the free CrF₃ surface area significantly increase with increasing content of Cr³⁺ loading. Optimum temperature for the reaction of HF with CCl₂=CHCl is 260°C, while with CF₃CH₂Cl it is 350°C, with flow ratios HFTCE = 61 andHFHCFC-133a = 101.     

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.     

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.     

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.     

Rectification behaviour of some metal ion–metal interfaces and concentration cells

The rectification behaviour of three metal ion–metal interfaces and 38 concentration cells was studied. The rectification in AlAl³⁺Al was 35% (–0.4 to +0.80 V d.c.) between 2.0–5.0 V a.c. and for ZnZn²⁺ Al³⁺Al cell was 20% (+0.20 to –0.30 V d.c.). Its negative d.c. potential showed some similarity to a tunnel diode. 20% rectification was obtained when each of Al, Zn, Mg half-cell was coupled with I^–, I₂Pt half-cell and Al half-cell was coupled with Fe³⁺, Fe²⁺Pt half-cell. When the Zn half-cell was associated with Cr³⁺, Cr₂O₇ ^2–Pt half-cell the rectification was 15%, whereas the rectification in all other concentration cells varied from 1 to 12%. The possibility of obtaining much higher percentage of rectification can be explored in a large number of other metal ion–metal interfaces and concentration cells which can be assembled in a similar manner using the table of standard reduction potentials. The characteristics of a concentration cell can be varied by change in concentration of metal ion, redox ratio, variation of pH, temperature, effect of different additives to the cell solution, irradiation of electrode surface etc. Consequently, it will affect the percentage of rectification which may be of some use in commercial applications.     

Temperature programmed oxidation of Cu/ZnO catalysts with N2O: an attempt for characterization of copper catalysts

For characterization of the surface structure of metallic copper formed on the support, temperature programmed oxidation (TPO) with N₂O was carried out over various Cu/ZnO catalysts. Four peaks of the N₂ formation (, , and ) were observed at 223, 400, 545 and 600 K in the TPO runs. The average copper crystallite size estimated from the sum of the amount of - and -peaks agreed fairly with those determined by X-ray diffraction and transmission electron microscopy. It was concluded that - and -peaks resulted from the oxidation of metallic copper atoms on the steps, corners and/ or defect sites, and on the flat sites of the surface of copper crystallites, respectively, while - and -peaks resulted from the bulk oxidation of copper.     

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.     

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.     

A chemically regenerative redox fuel cell

A novel chemically regenerative redox fuel cell is described. The electrode reactions are based on the following redox reactions: cathodic reaction: anodic reaction: VO ₂ ⁺ +2H⁺+e VO²⁺+H₂O (E ₀ +1V), SiW₁₂O ₄₀ ^5– SiW₁₂O ₄₀ ^4– +e (E ₀ 0V). Regeneration of the oxidant by direct oxidation with O₂ was achieved by using the soluble heteropoly acid catalysts, H₃PMo₁₂O₄₀ or H₅PMo₁₀V₂O₄₀, whereas regeneration of the tungstosilicic acid, H₃SiW₁₂O₄₀, was accomplished by direct reduction with H₂ utilizing small amounts of Pt, Pd, Rh, Ru or the soluble Pd-4, 4, 4, 4'-tetrasulphophthalocyanine complex as catalysts. Some aspects of the regeneration kinetics and their influence on the overall performance of the redox fuel cell are discussed.     

Dynamic mechanical properties of crosslinked polyisoprene under deformation

Summary Molecular motions of elastomers under deformations were observed through dynamic mechanical measurements. Composite master curves of dynamic moduli E and E and loss tangent tan over a wide range of frequency and in a state of elongation were obtained by the time-temperature superposition procedure. It is found that both moduli increase with strain, . The slope of the dispersion curve of E become more gradual with the increase in , while that of E is almost unchanged. The increment of E is generally larger than that of E, which does not agree with the N. W. Tschoegl prediction, E ^* ()=f() E _o ^* (), where E ^* () and E _o ^* () are complex moduli at the strain of and O, respectively, and f() is the function of only . The difference in the strain dependence of E from E was found to correspond to the strain dependence of the equilibrium modulus.     

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.     

FTIR spectroscopic investigation of the active sites on different types of silica catalysts for methane partial oxidation to formaldehyde

Several commercial silica samples showing different catalytic activities in the partial oxidation of methane (MPO) to formaldehyde have been investigated using FTIR technique. Two IR absorption bands at 893 and 909 cm^–1, observed upon dehydroxylation of the silica catalysts and assigned to reactive siloxane sites on the surface (strained siloxane bridges), were found to disappear upon heating in methane at high temperature. The catalytic activity increases together with the intensity of the bands due to such strained sites in the different SiO₂ samples.     

Synthesis and Structure of Large AlPO<Subscript>4</Subscript>-5 Crystals

Large, high quality, perfect hexagonally shaped AlPO₄-5 crystals have been crystallized using hydrothermal synthesis. The crystallization was carried out at 447 or 457 K with a crystallization time from one to four days and tripropylamine (TPA) molecules as template. The morphology of the crystals was observed with SEM. For the first time, the structure of the AlPO₄-5 crystal together with TPA template molecules has been successfully refined in space group P6cc by single crystal X-ray diffraction. The parameters are a = b = 13.725(3) Å, c = 8.473(3) Å, and = 120.0. The size of some crystals is up to 2.2 mm in c direction, or up to 0.31 mm in a or b direction. All observed angles and distances are within acceptable ranges: P–O = 1.50–1.54 Å, Al–O = 1.62–1.72 Å, O–P–O = 107–111, O–Al–O = 103–113 and P–O–Al = 147–150.     

Mixed impregnated thiosalt decomposition catalysts characterized by X-ray diffraction

We used the impregnated thiosalt decomposition method (ITD) to prepare catalysts of molybdenum sulfide promoted with cobalt in atomic ratios (r = Co/(Co + Mo)) ranging from 0.0 to 1.0. Measurements obtained by X-ray diffraction (XRD) show the presence of the MoS₂-2H phase in all mixed samples, and segregation of cobalt in two phases: Co₉S₈, forr 0.3, and CoS_1.035, for 0.3 r 0.5.     

On the NiMoO4 oxidative dehydrogenation of propane to propene: some physical correlations with the catalytic activity

The - and -phases of NiMoO₄ have been investigated with different techniques (X-ray diffraction, electrical conductivity, IR spectroscopy) in order to tentatively rationalise the different catalytic activities observed in the oxidative dehydrogenation of propane to propene. XRD analyses have shown that at 595 ° C, the -phase is already present but a temperature of 700 ° C is required to obtain a full conversion into a pure -phase. Electrical conductivity showed the presence of anionic vacancies. It is proposed that propene is formed by the reaction of propane with surface O^2- anions. The -phase is almost twice more selective in propene formation than the -phase for comparable conversion at identical temperatures. This could derive from different oxygen environments on the active catalytic site.     

Durability and thermal cycling of Ni/YSZ cermet anodes for solid oxide fuel cells

The long-term properties of Ni/yttria stabilized zirconia (YSZ) cermet anodes for solid oxide fuel cells were evaluated experimentally. A total of 13 anodes of three types based on two commercial NiO powders were examined. The durability was evaluated at temperatures of 850 C, 1000 C and 1050 C over 1300 to 2000h at an anodic d.c. load of 300mA cm^–2 in hydrogen with 1 to 3% water. The anode-related polarization resistance, R _P, was measured by impedance spectroscopy and found to be in the range of 0.05 to 0.7 cm². After an initial stabilization period of up to 300h, R _P varied linearly with time within the experimental uncertainty. At 1050 C no degradation was observed. At 1000 C a degradation rate of 10 m cm² per 1000 h was found. The degradation rate was possibly higher at 850 C. A single anode was exposed to nine thermal cycles from 1000 to below 100 C at 100 C h^–1. An increase in R _P of about 30m cm² was observed over the first two cycles. For the following thermal cycles R _P was stable within the experimental uncertainty.     

Catalytic behaviour and characterisation of CuO1−z(La2O3)z/2 based catalysts deposited on γ-Al2O3 and prepared in situ with 0.0 ⩽z⩽1.00, without and with addition of Pd

(CuO)_1–z(La₂O₃)_z/2 based catalysts with 0.0z1.0 supported on -Al₂O₃ have been prepared in situ and the phases formed have been identified by XRD, SEM and TEM/EDS studies. The catalyst with z=0.5 exhibited the best catalytic activity for oxidation of CO (T ₅₀=295 and 390C with degrees of conversions of 93 and 92% at 450C under rich and lean conditions, respectively) and C₃H₆ (291 and 414C; 93 and 83%) and reduction of NO (405C; 60 and 0%). This catalyst contained appreciable amounts of the perovskite phase LaAl_1–xCu_xO₃ and the enhanced catalytic properties are ascribed to the presence of this phase. Addition of Pd to this catalyst implied that the degree of conversion of NO increased and that the light-off temperatures for all involved gas species decreased. Ageing experiments revealed that LaAl_1–xCu_xO₃ decomposed and that Cu containing Pd particles were formed during this procedure which in turn deteriorated the catalytic properties of the catalyst.