Effect of carbon black composite (CBC) support properties on hydrodesulfurization performance of sulfided Mo and Co, and carburized Mo, catalysts

Carbon black composites (CBCs) have been prepared by pyrolyzing mixture of a carbon black with polyfurfuryl alcohol and then pretreated by oxidation with nitric acid, gasification with water steam or ammoxidation. The effects of the chemical character of the carrier surface, nature of the active metal phase and pH value of the impregnation solution on the catalytic activity towards the hydrodesulfurization (HDS) of thiophene of the CBC supported Mo (Co) catalysts were determined. It was stated that the catalytic properties of the CBC supported sulfides of Mo or Co and of Mo carbides are affected by the chemical character of the carrier surface. Generally, catalysts supported over basic surface CBC exhibit higher activity than those ones supported over CBC possessing acidic surface character. Co catalysts supported on acidic surface show lower activity (per mol of active metal) than Mo based ones supported on the same carrier. In the case of catalysts supported on basic CBC, Co exhibits distinctly higher activity than Mo. At the experimental conditions adopted for this study, CBC surface properties, active phase nature, and catalyst impregnation pH were found to exert a relatively small influence on both HDS and hydrogenation activities.     

Kinetic study of the deep hydrodesulfurization of dibenzothiophene over molybdenum carbide supported on a carbon black composite: Existence of two types of active sites

Hydrodesulfurization (HDS) is part of the hydrotreating process, which is an ensemble of several reactions (HDN, HDO, HDS, etc.) taking place simultaneously at the industrial scale. Only sulfur is currently submitted to drastic Europeans specifications and conventional commercial catalysts cannot reach the specifications at low cost. This paper presents the behavior of a potential substitute catalyst tested for the deep HDS of a model molecule such as the dibenzothiophene (DBT). The substitute is molybdenum carbide supported on a mesoporous carbon black composite of surface area 240 m² g⁻¹. A global kinetic study of the deep HDS of DBT (300 ppm S) was performed at 623 K and 5.0 MPa and a global kinetic model was proposed as well as global rate constants were calculated to obtain theoretical plots of concentration versus contact time to compare with the experimental data. The kinetic model and global kinetic orders were confirmed as an acceptable correlation was found between calculated and experimental data. Furthermore, the determination of the global kinetic orders indicated that two types of active sites must be present on the surface in order to explain the observed results.     

HDN of 1–4 tetrahydroquinoline over MoNxOy and NbNxOy: effect of transition metal, solvent and ammonia

Oxynitrides of early transition metals are bifunctional catalysts active in hydrodenitrogenation (HDN). The strength of the hydrogenating function and the acidic properties of molybdenum and niobium oxynitrides were investigated, as well as the inhibiting effect of ammonia and the effect of solvent (cyclohexane or tetradecane) on HDN of 1,2,3,4‐tetrahydroquinoline (1–4 THQ). Even under high hydrogen pressure (4.5 MPa) the reaction was found to be able to proceed without hydrogenation of the aromatic cycle of 1–4 THQ before C–N bond scission, which is not the case over sulfided NiMo supported catalysts in HDN. Experiments in presence of ammonia permitted to support a bifunctional dual site concept. This revised version was published online in July 2006 with corrections to the Cover Date.     

Optical constants of Nb2O5 anodic coatings on niobium

A method involving only normal reflectance measurements was developed to determine the optical properties of thin transparent layers formed on opaque substrates over a wavelength range including the visible spectrum. The spectral refractive index of Nb₂O₅ anodically grown on niobium samples up to 215 nm thick was obtained by this method and also the spectral phase change on reflection at the oxide-metal interface. Index determinations, however, require separate measurements of the layer thickness using, for instance, grazing incidence X-rays.     

Severe algoneurodystrophy of the right foot associated with prostatic cancer

The authors report 1 case of particularly severe reflex neurovascular dystrophy whose clinical course was marked by the discovery of a carcinoma of the prostate. There was improvement in the reflex neurovascular dystrophy despite hormonal therapy of the cancer. Reflex neurovascular dystrophy cannot be considered as a form of a paraneoplastic syndrome.     

Comparison of molybdenum carbide and tungsten carbide for the hydrodesulfurization of dibenzothiophene

The molybdenum and tungsten carbides (Mo₂C and W₂C) were synthesized, characterized and tested in hydrodesulfurization (HDS) of dibenzothiophene (DBT). The phase purity of these catalysts was established by X-ray diffraction (XRD), and the surface properties were determined by N₂ BET specific surface area (Sg) measurements, CO chemisorption and high-resolution transmission electron microscopy (HRTEM). The activities of catalysts were determined during the HDS of DBT at a temperature of 613 K and under a 6 MPa total pressure. Both molybdenum and tungsten carbides were active in HDS of DBT. The reactivity studies showed that molybdenum carbide was more active than tungsten carbide related to weight. However, W₂C was shown to possess stronger hydrogenating properties.     

Carbon black composites—supports of HDS catalysts

HDS activity of sulfided Mo (W) catalysts supported on carbon black composites (CBC) is affected by kind of functional groups present on the CBC surface. Oxidation of CBC with (NH₄)₂S₂O₈ produce functionalities with the highest acid strength and corresponding catalyst exhibits the highest HDS activity. Sulfided W/CBC is less active in thiophene HDS than corresponding Mo counterpart. The rate of thiophene HDS over Mo/“basic” CBC does not depend on the method of Mo deposition.     

Respiratory mechanics during laparoscopic cholecystectomy: the effects of the abdominal wall lift

The abdominal wall lift (AWL) has been proposed for laparoscopic cholecystectomy to reduce hemodynamic effects caused by carbon dioxide (CO2) and high intraabdominal pressures (IAP). Data concerning effects of AWL on respiratory mechanics are scant. We therefore used a noninvasive method to evaluate whether the AWL could offset these effects. The PETCO2, airflow, and airway pressure were continuously measured in nine patients undergoing laparoscopic cholecystectomy using an AWL with minimal CO2 insufflation. We used a least-squares method to calculate maximal airway pressure (Pmax), elastance (Ers), and resistances (Rrs) of the respiratory system. After CO2 insufflation, the initiation of AWL resulted in a significantly decreased IAP (from 13 to 6 mm Hg; P < 0.001) and Rrs (from 20.6 to 17.8 cm H2O.L(-1).s(-1); P = 0.029), whereas Ers was partly modified (34.0 to 33.3 cm H2O/L; not significantly different). With AWL, we hypothesized that the diaphragm remained flat and stiff, outweighing the beneficial effect of the decrease of IAP on Ers. PETCO2 significantly increased after AWL and at the end of the procedure. We conclude that AWL partly reverses the impairment of the respiratory mechanics induced by CO2 insufflation during laparoscopic surgery. IMPLICATIONS: The abdominal wall lift (AWL), acting on the abdominal chest wall, had some benefits during laparoscopic surgery by limiting CO2 peritoneal insufflation and several side effects, such as hemodynamics. We examined the consequences of this technique on respiratory mechanics in nine patients undergoing laparoscopic cholecystectomy. Our findings suggest that the AWL decreases intraabdominal pressure and respiratory resistances without a significant effect on respiratory elastance.     

Hydrodenitrogenation of indole over Mo2C catalyst: Insights into mechanistic events through DFT modeling

The molecular reaction mechanism of hydrodenitrogenation of indole was studied using density-functional theory calculations of the adsorbed o-ethylaniline surrounded by mobile hydrogen atoms. It was found that the hydrogenation of o-ethylaniline occurs through two steps: consisting in redistribution of the π electron density to form multiple partial MoC(ring) bonds with the surface upon adsorption, and a subsequent hydrogen attack directed on the aromatic ring or the amine group. The direction of the hydrogen attack and the associated energy barriers determine the rate constants of the early (DDN, direct denitrogenation) and late (HYD, hydrogenation) nitrogen removal steps, and thus rules the selectivity of indole hydrodenitrogenation to ethylcyclohexane or ethylbenzene.