Maria Cristina Abello

Selective oxidation of propane on MgO/γ‐Al2O3‐supported molybdenum catalyst: influence of promoters

The influence of promoters, potassium and samarium, on molybdenum supported over MgO–γ‐Al2O3 catalyst has been investigated in the oxidative dehydrogenation of propane. The acidities of catalysts were determined by temperature‐programmed desorption of NH3 and by decomposition of 2‐propanol. The K‐promoted catalyst showed the lower acidity followed by the Sm, whereas the unpromoted sample showed the highest acidity. The higher the acid character of the catalyst, the lower the selectivity to propene. Redox properties determined from EPR spectra change with the addition of the promoter. A parallelism between Mo6+ reducibility and catalytic activity was found.

Synergy effects in the oxidative dehydrogenation of propane over MgMoO4-MoO3 catalysts

Oxidative dehydrogenation of propane was studied over MgMoO4-MoO3 catalysts with a wt% of MoO3 varying from 0 to 100. The samples were characterized by XRD, EPR, DTA, laser Raman, and BET. The catalytic behavior of the mechanical mixtures was quite different from that of pure phases. These differences were discussed in terms of possible synergy effects between the phases. Propane conversion and selectivity to propene were closely related to the change in redox properties of the catalysts due to the appearance of Mo5+ ions.

Temperature-programmed desorption study of the acidic properties of γ-alumina

Temperature-programmed desorption was used to investigate the acidic properties of a commercial γ-alumina. A model which accurately interprets the thermodesorption spectra was developed by means of the Monte Carlo method. A discrete distribution in strength was observed and the relative abundance of the different types of active sites was determined.

Preparation and characterization of MgO-γ Al2O3 composite oxides

Abstract Studies of the chemical preparation, surface area, pore distribution, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectra (XPS) and acid-base properties of magnesia–alumina composite oxides were carried out. The preparation method led to supports with high surface areas where Mg was homogeneously distributed upon the surface. The base properties of the composite oxides can be controlled by the Mg loading for an optimum catalyst performance.

Synthesis of 1,1-Diethoxyethane From Bioethanol. Influence of Catalyst Acidity

The reaction of isopropanol decomposition was carried out with the purpose of classifying, in terms of acidity, different catalysts used in the synthesis of 1,1- diethoxyethane. The 1,1-diethoxyethane production is clearly correlated with the acidity of the solids.

Oxidative Conversion of Propane over Al2O3-Supported Molybdenum and Chromium Oxides

Oxidative dehydrogenation of propane has been studied on Mo/γ-Al2O3 catalysts with 13 wt% of MoO3 and promoted with Cr. The catalysts were characterized by BET, X-ray diffraction, XPS, TPR, TPO and isopropanol decomposition. The ODH results indicated an important increase in propane conversion with Cr loading increase from 0 to 5 wt%. At 773 K the conversion increased 1.5 times whereas the selectivity to propene was not significantly modified. The higher activities obtained on Cr-doped catalysts provide for the technologically important possibility of carrying out the reaction at lower temperatures.

Methanol steam reforming over Cu/CeO2 catalysts: influence of zinc addition

Methanol steam reforming reaction was studied over Cu(5 wt.%)/CeO2 with and without the presence of Zn. The Zn addition decreased the Cu+2 reducibility and increased the oxygen mobility of ceria. The main products were CO2 and H2 with small amount of CO. Selectivity to CO decreased with the Zn addition and it was lower at lower reaction temperatures and lower space velocities. At 230 oC and W/FMeOH = 648 g min mol-1 selectivities to H2 and to CO2 were 100% on Zn/Cu/Ce. The catalytic results indicated that CO was mainly a secondary product formed from reverse water gas shift reaction.

Ammonia decomposition on polycrystalline Pt at pressures between 1.3 and 93 kPa

The kinetics of ammonia decomposition on polycrystalline Pt at temperatures between 600 and 1700 K and at pressures between 1.3 and 93 kPa were measured and correlated with a Langmuir-Hinshelwood unimolecular reaction rate expression. This rate expression had previously been shown to fit data in the same temperature range for pressures between 2 and 1400 Pa.AbstractИзмерена кинетика разложения аммиака на поликристаллической Pt в интервале температур 600–1700 К и при давлениях от 1,3 до 93 кПа, которая подчиняется уравнению Пангмюра-Хиншельвуда для скорости мономолекулярной реакции. Это уравнение скорости, как уже ранее установлено, соответствует данным в том же интервале температур, но для давлений от 2 до 1400 Па.

Synthesis of Nickel Nanoparticles Supported on Carbon Using a Filter Paper as Biomorphic Pattern for Application in Catalysis

Nickel catalysts supported over an amorphous carbon were obtained by a one-step synthesis method based on the mineralization of cellulosic paper impregnated with a salt of nickel. The effect of the mineralization temperature on material characteristics was studied. The characterization of samples revealed the formation of nickel nanoparticles well dispersed on the carbonaceous matrix with an average diameter near to 5 nm. The samples showed high surface areas and they retained the original fibrous paper morphology.

CHARACTERIZATION OF CeO2 DOPED MgAl2O4 PREPARED BY THE CHELATING AGENTS-ASSISTED IMPREGNATION METHOD

MgAl2O4 spinel employed as support of reforming catalysts was doped by CeO2. The samples were prepared by wet impregnation from aqueous solutions of cerium nitrate, with and without chelating agents. The chelating agents used were ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA) and citric acid (CA) at different pH of impregnation. The solids were characterized by TG, XRD, SBET, TPR, SEM-EDX and CO2−TPD. Nanoparticles of CeO2 between 5 and 6.8 nm were obtained by the thermal decomposition in air at 600 °C. The surface cerium reduction occurred in a wide temperature range of 450° to 670 °C. The use of citric acid at pH= 8 led to the lowest crystallite size of CeO2 and the lowest interaction with the spinel. The H2 consumption and extent of CeO2-support interaction did not show a clear dependence with the CeO2 crystallite sizes. The use of chelating agents in the impregnation step did not modify the total basicity. Slight changes in the strength of weak basic sites were observed.