Abstract Silicoaluminophosphates SAPO-5 and SAPO-11 were synthesized using the hydrothermal method, 170 ºC with triethylamine and dipropylamine as the structure directing agents, respectively. This work aimed the incorporation of boron into the structures obtained by modifying the composition of the system, using as a reaction equation: Al2O3:P2O5:x SiO2: yB2O3:1,5TEA (or DPA):50H2O, with x, y=0-0.2. The phase was identified by XRD and characterized by FTIR, TGA/DTG, TPD-NH3 and nitrogen adsorption at -196°C. The structure parameters confirmed the obtaining of pure structures, showing a slight contraction in the parameters of the unit cells, indicating the presence of boron in the crystal lattice. The Brønsted sites, were modified up to a maximum of boron (y = 0.1) and for higher content, the acidity was not significant. The modification of weak acidity related to the appearance of isolated BO3 groups, indicating that the silicon atoms were not sufficiently distributed for the formation of sites.

ABSTRACT Cobalt and niobium oxide solids modified with alkaline earth metals (Mg, Ca, and Sr) were synthesized and characterized to compare the second element effect on the catalyst structural and chemical properties. The materials were prepared by co-precipitation of cobalt nitrate and niobium oxalate solutions using ammonium hydroxide as precipitating agent. The samples were characterized by XRD, SEM, Ra-man, BET, TPR, ammonia TPD and cyclohexane dehydrogenation reaction (CHD). Results showed that Mg, Ca or Sr addition changed cobalt niobate crystalline structure, leading to alkaline earth metal nio-bates with lower crystallinity. It was observed that Mg, Ca or Sr increased the solids acidity and changed cobalt niobate reduction behavior so that the lowest amount of metallic cobalt was obtained when Mg was incorporated. Modifiers also decreased cobalt niobate dehydrogenation activity. This effect was higher with Mg or Sr addition.

In this paper, magnesium aluminate spinels were prepared by microwave-assisted combustion, using urea as fuel. In order to evaluate the effect of the urea excess used in the synthesis, its mass was added in a range of 1.0 to 2.5 times the stoichiometric amount required. The materials produced were characterized by TGA, FTIR, XRF, XRD, BET, SEM and TEM. The results demonstrated that magnesium aluminate spinel was formed in all solids, but the crystallinity degree and the specific surface area increased according to the amount of urea that was used in the synthesis. The use of excess fuel in the preparation was therefore advantageous, since it eliminated the need of the calcination step, at high temperatures, in order to stabilize the spinel phase and improve the crystallinity of the solid. The heat generated in the combustion process was sufficient to develop the formation of a nanocrystalline structure and produce high purity materials, with a save of 99.4% in energy.

Abstract In this paper, a new way for γ-alumina synthesis was proposed, the raw material being aluminum powders obtained by high-energy milling of aluminum cans. This seems a good option for this metal recycling and energy saving, as well as hydrogen production. The materials were prepared by precipitation techniques, in which aluminum powders reacted with hydrochloric acid, giving aluminum chloride, which was subsequently transformed into aluminum hydroxide by reaction with ammonium hydroxide or sodium hydroxide as precipitant agents, and finally into γ-alumina by calcination. Results showed that the used preparation methods gave a γ-alumina structure, confirmed by XRD, with surface areas values (174 and 204 m2 g-1) close to those of a commercial γ-alumina Cyanamid Ketjen (180 m2 g-1) or an alumina prepared by a typical precipitation route (203 m2 g-1). Using sodium hydroxide as precipitant agent turned out to be more ecologically compatible since it did not release harmful environmental compounds.