The nature of metal oxide on adsorptive and catalytic properties of Pd/MeOx/Al2O3 catalysts

The role of ceria, niobium and molybdenum oxides on the promotion of the NO reduction by CO was studied. A bifunctional mechanism was discussed as a function of both the nature of interaction between metal oxide and palladium and the redox properties of each metal oxide.

The NO dissociation was better on the Pd/MoO₃/Al₂O₃ catalyst than on the Pd/CeO₂/Al₂O₃ and Pd/Nb₂O₅/Al₂O₃ catalysts. The explanation for the very high N₂ production on Pd–Mo catalyst during the TPD analysis may be attributed to the NO+Me^δ+ stoichiometric reaction.

The promoting effect of a reducible oxide for the NO+CO reaction at low temperature can be ascribed mainly to its easiness for a redox interchange and its interaction with the noble metal particles. This would increase the surface redox ability and favor the dynamic equilibrium needed for high N₂ selectivity.     

A radiation tolerant phototube power supply for the electromagnetic calorimeter of the HERA- experiment

The design of the phototube power supply for the HERA-B  Electromagnetic Calorimeter is presented. A choice of the solution on the basis of the Cockcroft–Walton voltage multiplier is validated. Schematics developed are discussed. A special section describes the behaviour of the crucial components under irradiation since radiation tolerance becomes one of the most important items in the severe HERA-B  radiation environment. Finally, performance achieved is presented.     

NO x Reduction by Ethanol on Pd/Sulphated Zirconia

The NO reduction by ethanol was studied on palladium catalyst supported on sulphated zirconia. Temperature programmed desorption of NO and ethanol (TPD) and temperature programmed surface reaction (TPSR) analyses as well as catalytic tests in reducing and oxidizing conditions (O₂ presence), besides diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed the formation of intermediate species during the reaction, such as ethoxy species that reacted forming ethylene. Besides dehydrogenate formed adsorbed acetate species, which than decompose and/or react with hydroxyls of the support. The sulphated zirconia support increased the acid sites with the formation of strong Brönsted sites, favoring the formation of ethoxy species. Acetate species also react with NO adsorbed on Pd forming N₂, N₂O, CO and CO₂. The excess of O₂ favored ethanol oxidation to CO₂, consequently less ethanol was available to react with NO _x .     

NO x reduction by ethanol on Pd/zeolites-effect of oxygen

The reduction of NO by ethanol on palladium catalysts supported on NaZSM-5 and HZSM-5 zeolites was studied. Temperature programmed techniques, such as desorption of ethanol, NO and surface reaction (TPSR) analyses, besides NH₃ (NH₃–TPD), as well as, FTIR after pyridine adsorption were used to accomplish reaction products and surface properties. Results show that NaZSM5 and HZSM5 present different amounts of Lewis and Brönsted acid sites, which affect strongly the carbon product distribution, but not the nitrogen selectivity. NO reaction with ethanol in the presence of oxygen occurs only over the metal and is independent of the acid sites.     

Nickel–Promoted Molybdenum or Tungsten Carbides as Catalysts in Dry Reforming of Methane: Effects of Variation in CH4/CO2 Molar Ratio

Ni–Mo₂C and Ni–WC were evaluated in dry reforming of methane employing different CH₄/CO₂ ratios. Ni–Mo₂C remained active under an excess of CH₄, but deactivation occurred under an excess of CO₂. Ni–WC was resistant to excess of CO₂ but showed carbon deposition under excess of CH₄.

Graphic Abstract

     

Stability of Ni and Rh–Ni catalysts derived from hydrotalcite-like precursors for the partial oxidation of methane

In this work, NiMgAl and RhNiMgAl catalysts prepared from HTLCs precursors were investigated for the Partial Oxidation of Methane (POM) at 550 and 750 °C. Samples have been characterized by XRD, TPR, H₂ chemisorption, TPSR analyses, XPS, field emission scanning electron microscopy and Raman spectroscopy. NiMgAl catalysts with high Ni content (40 and 16 wt%) showed high stability and high methane conversion for POM. On the other hand those with lower Ni content (NiHT15 and NiHT25, with 6 and 4 wt%) exhibited low catalytic activity with low H₂/CO ratio (<2) and fast deactivation. In RhNiHT25 (0.6 wt. % Rh), the Ni reducibility was improved, increasing the methane conversion and hydrogen selectivity. In addition, the noticeable increase in stability was related to the absence of carbon deposition after 30 h on stream at 550 °C. These results show that RhNiHT25 is promising for application in membrane reactors to produce high purity hydrogen.     

Influence of oxygen and promoting effect of barium on the reduction of NOx by ethanol on Pd/ZrO2 catalyst

The NO reduction by ethanol over barium promoted Pd/ZrO₂ catalyst and the effect of the oxygen on the selectivity were studied. The catalysts were prepared by incipient wetness impregnation with 14.3% of Ba over zirconia and 1% of palladium. The specific surface areas were 58 and 47 m²/g and the dispersions of Pd were 37% and 30% for the Pd/ZrO₂ and Pd–Ba/ZrO₂ catalysts, respectively. The X-ray diffraction patterns indicate the presence of monoclinic zirconia phase on the support and BaCO₃, which is decomposed at 715 and 815 °C. Temperature programmed desorption profiles of NO on Pd/ZrO₂ and Pd–Ba/ZrO₂ catalyst showed a huge amount N₂ formation for the promoted Ba catalyst. Catalytic results showed high NO conversion even at low temperature, in accordance with the TPD results and an increasing selectivity to N₂ when compared with Pd/ZrO₂. The effect of O₂ in the NO_x reduction with ethanol provoked less NO dissociation and lower selectivity to methane.     

The electromagnetic calorimeter of the HERA-B experiment

The electromagnetic calorimeter of the HERA-B experiment built at the HERA proton accelerator at DESY (Hamburg) is described. The construction characteristics of the detector, of the related front-end, readout, trigger and service electronics are discussed together with the constraints and the motivations which inspired the design philosophy. The detector performance are presented as obtained from the analysis of the data acquired during the HERA-B running period, including calibration procedures and achievements and the electron identification capability exploiting a method, proposed here for the first time, based on the observation of the associated bremsstrahlung γ. Finally, some observed physical signals and a short overview of the main obtained physics results are presented.     

Carbon Nanotubes Networking in Styrene-Butadiene Rubber: A Dynamic Mechanical and Dielectric Spectroscopy Study

The study of the reinforcement network in elastomer compounds is one of the most relevant issues for the application of these materials because their properties are strongly dependent on the obtained morphology. To this regard, the viscoelastic and dielectric behavior of vulcanized styrene butadiene rubber (SBR) reinforced with different amounts of carbon nanotubes (CNT) have been investigated and compared with the vulcanized unfilled SBR and the vulcanized SBR samples reinforced with a conventional amount of carbon black (40 phr). Differential scanning calorimetry (DSC) measurements have been carried out to highlight possible differences of the glass transition temperatures for all the reinforced compounds. The percolation threshold value of the nanocomposite samples has been estimated by dielectric analysis. Finally, dynamic mechanical analysis (DMA) measurements have been performed in tensile mode in the temperature range of −60 to 80 °C to obtain both E′ and E′′. From these experimental data, the master curve for each sample has been estimated by using the time–temperature superposition principle in combination with the vertical shift approach. From the analysis of this latter, the activation energy, associated to the thermal movement of the reinforcement network, has been calculated to better elucidate the reinforcement mechanism in the nanocomposites.