Akinori Maezawa

Active sites of molybdenum sulfide catalysts supported on Al2O3 and TiO2 for hydrodesulfurization and hydrogenation

A comparative characterization of sulfided MoO3Al2O3 and MoO3TiO2 catalysts was conducted by using LRS, XPS, IR, and TDS of NO. On the basis of the characterization, the active sites were estimated for the hydrodesulfurization of thiophene and hydrogenation of butadiene. The LRS and XPS results indicated that sulflded MoO3Al2O3 catalysts consisted of MoS2-like phases and Mo(V) species, while sulfided solMoO3TiO2 catalysts was fully sulfided to MoS2-like phases. The TDS of NO demonstrated that there were at least two distinctly different NO adsorption sites on sulfided molybdenum catalysts. They were assigned to triply (α) and doubly (β) cus Mo-sites on the basis of the H2Sue5f8NO coadsorption. The fractions of α- and β-sites depended on both molybdenum loading and support, suggesting a variation in the morphology of MoS2-like phases. The number of α-sites was linearly correlated to the activity for the hydrogenation of butadiene at 273 K, being independent of the support. This suggests that α-sites are responsible for the hydrogenation. Hydrogenation cycles involving α-sites are proposed at low and high reaction temperatures and in the presence and absence of H2S. With the HDS reaction, separate parabolic correlations were obtained for the MoO3Al2O3 and MoO3TiO2 catalysts between the activity and NO adsorption, suggesting dual sites as the HDS active centers and negative effects of molybdenum sulfide-support interactions.

Electronic structure of zeolites studied by X-Ray photoelectron spectroscopy

Abstract The electronic structure of zeolites was systematically investigated by utilizing XPS. Zeolites A, X, Y, and mordenites in their sodium and decationized forms as well as the series of alkali metal cation-exchanged X and Y zeolites were examined. The electronic structure of zeolites was demonstrated to depend strongly on both the composition and the cation involved. It is suggested that the basic strength of framework oxygen increases with increasing Al content regardless of the crystal structure and with the decreasing electronegativity of the counter cation. These results explain well certain catalytic properties of alkali metal cation-exchanged zeolites. On the basis of the XPS results, the nature of chemical bonding in zeolites is discussed.

Highly dispersed molybdenum sulfide catalysts prepared from Mo(CO)6 encaged in a zeolite

Abstract Molybdenum sulfide catalysts were prepared from Mo(CO)6 encaged in zeolites and characterized by XPS, IR and NO adsorption. It was demonstrated that highly dispersed sulfides were produced by a reaction between molybdenum subcarbonyl species and H2S at 373 K. The molybdenum sulfide in a KY or NaY zeolite was found to show a higher catalytic activity per Mo for the hydrodesulfurization (HDS) of thiophene than a molybdenum sulfide catalyst prepared by impregnation procedures. The dependence of the turnover frequency of the HDS on the zeolite and support oxide is explained in terms of the structure of sulfided molybdenum and of the diffusion limitations of the reactant and products. The basic strength of the zeolite is suggested to control the reactivity of the subcarbonyl species toward H2S and the dispersion degree of the molybdenum sulfide. On the basis of IR, temperature-programmed decomposition and XPS results, the subcarbonyl species, Mo(CO)3, was shown to form a complex, Mo(CO)3(SH)ads, by reaction with H2S at room temperature.

Stoichiometry of molybdenum subcarbonyl species encaged in NaY and HY zeolites

Pour cette etude, la decomposition du CO par temperature programmee et le marquage isotopique par carbone 13 sont employes

Utilization of Ultrasonic Energy in a Photocatalytic Oxidation Process for Treating Waste Water Containing Surfactants

A system for treating waste water containing surfactants using a photo-oxidation catalyst combined with ultrasonic irradiation was investigated. The system consisted of two reaction chambers installed with ultrasonic transmitters of different frequencies to enhance the photo-catalytic reaction as well as to recover the photocatalyst particles used. An ultrasonic transmitter with a frequency of 200 kHz was used the reaction to enhance in the first chamber. An ultrasonic transmitter with a frequency of 28 kHz was installed for particles recovery in the second chamber. Glass beads (hereinafter GB) were used as the collectors as well as the accelerators of the agglomerated photocatalyst particles under ultrasonic irradiation. Waste water containing a surfactant, i.e., polyoxy-ethylene-alkyl-ether (C14H29O(CH2CH2)7H, hereinafter SS-70) with an initial concentration of 100 ppm and a volume of 1000 ml was used as a sample. It was confirmed that after three times of recycling tests there was no significant loss in catalyst activity.

Thermal stabilities of hexacarbonyl and subcarbonyls of molybdenum encapsulated in NaY and NaX zeolites

Decompositions of Mo(CO)6 and the resulting subcarbonyl species adsorbed on NaY and NaX zeolites have been investigated utilizing i.r., temperature-programmed decomposition and X.p.s. techniques. It was found that Mo(CO)6 encapsulated in the NaX zeolite was considerably less stable than that contained in the NaY zeolite, while intermediate subcarbonyl species, Mo(CO)3ads, showed a completely reversed thermal stability. The drastic difference in the stabilizing properties between X and Y zeolites is thought to result from the difference in the basic strength of the zeolite framework oxygen. The structure of Mo(CO)3ads is proposed on the basis of i.r. spectra. The X.p.s. results suggest that the adsorbed Mo(CO)3 species is decomposed to Mo-metal aggregates at 473 K.

Physicochemical characterization of ZnO/Al2O3 and ZnO–MoO3/Al2O3 catalysts

The interaction modes of ZnO with Al2O3 and MoO3/Al2O3 catalysts have been investigated as a function of ZnO content (1–30 wt% with respect to Al2O2) and calcination temperature (400–800 °C) by using X.p.s., A.e.s., and other physicochemical techniques. Particular attention was paid to the depth distribution of zinc ions in the surface layer of Al2 O3 by using the Zn LMM/Zn 2p3/2 intensity ratio coupled with Ar+-sputtering techniques. Zinc ions are highly dispersed, forming a ‘surface spinel’ irrespective of the calcination temperature in ZnO/Al2O3 catalysts having a low ZnO content,(<10–15 wt%). With the ZnO/Al2O3O3 catalysts containing 1–2 wt% ZnO, it has been found that zinc ions are retained in the surface layer of the Al2O3, even when calcined at 800 °C. In the case of ZnO/MoO3/Al2O3 catalysts an enhanced segregation of zinc ions in the surface layer of Al2O3, was deteced, suggesting the occurrence of the interaction with pre-existing molybdates on Al2O3 while no appreciable effects of ZnO on the distribution and reduction behaviour of the molybdenum species were observed.

Molybdena-alumina interaction chemistry: effect of preadsorbed sulphate and fluorine anions on the dispersion of molybdenum

Abstract On the basis of X-ray photoelectron spectroscopic and temperature-programmed reduction results, molybdena-alumina interaction modes were demonstrated to be strongly modified by the preadsorption of sulphate or fluorine anions. Before calcination, the dispersion of molybdenum was considerably suppressed by the pre-existing anions, suggesting that basic hydroxyl groups on alumina play a decisive role in the initial dispersion of molybdates. On calcination at 823 K, the dispersion of molybdenum was greatly improved. It was found that considerable fractions of the SO2−4 and F− anions were eliminated by the impregnation of molybdenum and subsequent calcination at 823 K. The reduction temperature of sulphate anions of alumina was shown to be significantly decreased by the presence of molybdena in the proximity.

Experiments on SO2 Absorption in a Bag Filter Based on the Grain Model

A mathematical model dealing with the removal of So2 by solid absorbent in a bag filter is proposed. The model assumes a situation similar to that of a fixed bed reactor and describes the phenomena and kinetics of the process for the So2-Ca(OH)2 reaction system. The model is based on the grain model concept, where the diffusion coefficient of gas in the particles/pellet is assumed to vary during the reaction. Runge-Kutta-Gill and finite difference methods were used to calculate the reaction rate constant, ks, and the coefficient of gas diffusion in the solid grain, Ds, through best fitting with the experimental data under a temperature range of 120-190°C. The effects of certain parameters, such as humidity and temperature, were investigated. Assuming the validity of the Arrhenius law, the activation energies were calculated for both the reaction, Er, and the coefficient of gas diffusion in the solid grain, EdThe results thus obtained using the proposed model are in good agreement with those previously reported in the literature.

Highly selective hydrogenation of buta-1,3-diene to cis-but-2-ene over molybdenum subcarbonyl species encapsulated in alkali metal cation exchanged Y-zeolites

Molybdenum subcarbonyl species encaged in a zeolite, particularly in LiY, showed a high activity for the selective hydrogenation of buta-1,3-diene to cis-but-2-ene (>96%), providing the first example of hydrogenation activity of molybdenum subcarbonyl species immobilized on inorganic matrices.