J.A. Melo-Banda

Hydrotreating of heavy vacuum gas oil (HVGO) on molybdenum and tungsten nitrides catalytic phases

Abstract A series of supported and unsupported Mo2N and W2N phases were synthesized by means of the treatment under ammonia atmosphere at 700°C of Mo and W oxides. The X-ray diffraction and electron microscopy techniques verified the formation of the Mo2N and W2N ceramic phases, while the N2 adsorption (BET) was used to determine the surface areas, between 46–133xa0m2/g for Mo2N (unsupported) and 81–101xa0m2/g for W2N (unsupported). The supported phases had surface areas between 109–113 and 109–122xa0m2/g, for Mo2N/Al2O3 and W2N/Al2O3, respectively. The catalytic hydrotreating of a heavy vacuum gas oil (HVGO) derived from Maya crude (i.e. 2.21xa0wt.% S, 0.184xa0wt.% N2) was performed on both, supported and unsupported Mo nitrides and W nitrides, which promoted the HDN reaction preferentially, up to 26.6% on Mo2N/Al2O3 and up to 22.3% on W2N/Al2O3, against 3.26% on the reference catalyst, i.e. CoMo/Al2O3 at 350°C and 80xa0kg/cm2. Also, the rates for HDN increased with the crystallite size in the unsupported W2N series. Also, the pore volume and mean pore diameters of the Mo2N/Al2O3 and W2N/Al2O3 series improve substantially with respect to the pure ceramic phases.

Polypyrrole microcontainer structures and doughnuts designed by electrochemical oxidation: an electrochemical and scanning electron microscopy study

Abstract Scanning electron microscopy (SEM) is employed to monitor the surface morphology of polypyrrole films (PPy) grown on different working electrodes (i.e., vitreous carbon and Au (111)) under diverse experimental conditions (i.e., dynamic vs. static potential protocols) and anion dopants (i.e., I- and F-). The morphology of the electrosynthesized films includes rings (doughnuts) and microcontainers, and depends on the synthesis parameters such as the electropolymerization method, the nature of the substrate, the anion dopant, and the sequence of sandwich composite growth. The formation of well-defined rings and microcontainers is attributed to overoxidation occurring during the formation of F--doped PPy. It is possible to design microcontainers by controlling the overoxidation and degradation of the polymer surface.

Hydrotreating of heavy vacuum gas oil on unsupported and supported Mo-, W-, Nb- nitrides

This work shows the results obtained in hydrotreating reaction from using a real fraction. The results showed a relationship with the structural and crystalographyc properties of the used materials.

Alkylation of Benzene with Propylene over H3PW12O40 Supported on MCM-41 and -48 Type Mesoporous Materials

The present work, the HPA Keggin structure was supported on four different MCM phase types (hexagonal, spherical, elliptical, and cubic); their catalytic properties were tested in the alkylation of benzene with propylene in order to produce cumene. In the reaction, parameters like propylene flow, reaction temperature, phase type, as well as WHSV-1, HPA, and Cs content in the best MCM phase support were studied. The results showed that the MCM-48 with (30 wt. % HPA) catalyst had the best behavior in catalytic activity, showing the higher conversion and selectivity toward cumene as the main product.

Studies on the Catalytic Activity of Sulfated Zirconia Promoted with Cerium Oxide

Pure zirconia, sulfated zirconia and sulfated zirconia modified with 2, 3, 5 and 10 wt. % of cerium oxide were synthesized by sol-gel method. Pt phase was impregnated on the supports using the incipient wet technique. Sulfated zirconium oxide showed tetragonal phase only. Addition of cerium to sulfated zirconia did not modify the tetragonal phase but produced a marked effect on the surface area. Low cerium content may greatly increase the surface area; however, too high cerium content (10 wt.%) may decrease the surface area. Pore size had influence on the catalytic activity and ZrO2 acidity was favored by the sulfate ion incorporation. All catalysts having Brönsted and Lewis acid sites were active in the n-hexane isomerization. The highest n-hexane conversion (40%) and selectivity towards DMB (26%), 2-methyl pentane (61%) and 3-methyl pentane (13%) were reached over the catalyst with 10 wt. % cerium oxide. In addition, sulfated zirconium oxide presented high selectivity of light products (< C6), which indicated that the addition of this doping agent (CeO2) made the catalysts more selective toward the desired reaction products.

Catalytic Properties of Ni-Mo Carbide and Nitride Phases Supported on SBA-15 and -16 in the Hydrodesulfurization of DBT

In this paper, the incorporation of carbide and nitride phases supported on mesoporous materials like SBA type is described in order to obtain a better material than commercial catalysts (NiMoS/Al2O3, Sg=269 m2.gr-1) specifically in the HDS of dibenzothiophene. The XRD patterns exhibit the presence of carbide and nitride phases in each series, respectively. In the nitride materials, the presence of oxide phases was more evident than in the carbide catalysts. The principal product was biphenyl (BF) for all the analyzed series. This behavior suggests that the DBT desulphurization pathway for the carbide materials was similar to that of sulfide catalysts. Bicyclohexyl (BCH) was analyzed as a product, and cyclohexylbenzene traces (CHB) were determined in a single catalyst (NiMoC-2%P/SBA-16). This was attributed to the hydrogenation character of carbide catalyst reported previously.

Chitosan-Starch Films with Natural Extracts: Physical, Chemical, Morphological and Thermal Properties

The aim of this study is to analyze the properties of a series of polysaccharide composite films, such as apparent density, color, the presence of functional groups, morphology, and thermal stability, as well as the correlation between them and their antimicrobial and optical properties. Natural antioxidants such as anthocyanins (from cranberry; blueberry and pomegranate); betalains (from beetroot and pitaya); resveratrol (from grape); and thymol and carvacrol (from oregano) were added to the films. Few changes in the position and intensity of the FTIR spectra bands were observed despite the low content of extract added to the films. Due to this fact, the antioxidants were extracted and identified by spectroscopic analysis; and they were also quantified using the Folin-Denis method and a gallic acid calibration curve, which confirmed the presence of natural antioxidants in the films. According to the SEM analysis, the presence of natural antioxidants has no influence on the film morphology because the stretch marks and white points that were observed were related to starch presence. On the other hand, the TGA analysis showed that the type of extract influences the total weight loss. The overall interpretation of the results suggests that the use of natural antioxidants as additives for chitosan-starch film preparation has a prominent impact on most of the critical properties that are decisive in making them suitable for food-packing applications.