Nielson F.P. Ribeiro

Aqueous-phase reforming of glycerol using Ni–Cu catalysts prepared from hydrotalcite-like precursors

Ni–Cu catalysts derived from hydrotalcite-like compounds were prepared with 20 wt% of NiO and 0, 5 and 10 wt% of CuO, and evaluated in the aqueous-phase reforming of glycerol. The catalysts were characterized by chemical composition, textural analysis, crystalline structure, reducibility and acidity. The reaction was performed in a continuous flow reactor with a solution of 10 vol% glycerol, at 250 °C/35 atm and 270 °C/50 atm. The maximum glycerol conversion at 250 °C/35 atm was 70% and total conversion of glycerol was achieved at 270 °C/50 atm with Cu-containing catalysts. In the gas phase, the H2 selectivity was around 40% and CO selectivity was very low at 250 °C/35 atm. The addition of Cu decreased the CH4 formation. The main products formed in the liquid phase were acetol and lactic acid and a small quantity of propanoic acid. The Cu-containing catalysts showed higher formation of acetol, which was correlated with their higher acidity. Characterization of the spent catalysts revealed a sintering of the metal particles, although no deactivation was observed during 6 h of reaction.

Production of hydrogen from steam reforming of glycerolusing nickel catalysts supported on Al2O3, CeO2 and ZrO2

Abstract Nickel catalysts supported on Al2O3, CeO2 and ZrO2 were prepared by wet impregnation method and evaluated in steam reforming of glycerol. The catalysts were characterized by chemical composition, textural analysis, crystalline structure and reducibility. The structural characterization of the catalysts revealed a good dispersion of Ni particles using the Al2O3 support, needing higher reduction temperature. The reactions were performed at 500°C with 10 vol.% glycerol solution in a continuous flow reactor. All catalysts showed conversions close to 100%. The selectivity to gas products and formation of liquid by-products were found to be dependent on the type of support. The H2 selectivity showed the following trend: ZrO2 > Al2O3 ≈ CeO2. The catalyst supported on CeO2 showed low activity for water-gas shift reaction, with the highest CO selectivity. All catalysts presented a low formation of CH4. In the liquid phase some by-products were identified (hydroxyacetone, acetic acid, lactic acid, acetaldehyde, acrolein and ethanol) and secondary reaction routes were proposed. Coke formation was higher on Ni/Al2O3 catalyst, but no deactivation was observed during 8 h of reaction.

Removal of boron from oilfield wastewater via adsorption with synthetic layered double hydroxides.

Hydrotalcite is a layered double hydroxide (LDH) consisting of brucite‐like sheets of metal ions (Mg‐Al). In this work, hydrotalcites were synthesized, and boron removal from oilfield wastewater was evaluated. LDHs were synthesized using the co‐precipitation method. The calcined products (CLDHs) were obtained by heating at 500°C and characterized using X‐ray diffraction, X‐ray fluorescence, thermogravimetric analysis and the specific surface area (BET). The affinity of LDHs for borate ions was evaluated for calcined and uncalcined LDHs as a function of contact time, initial pH of the oilfield wastewater (pH ∼ 9) and the LDH surface area. The tests were conducted at room temperature (approximately 25ºC). The results indicated that 10 min were needed to reach a state of equilibrium during boron removal for calcined LDHs due to the high surface area (202.3 m2 g−1) regardless of the initial pH of the oilfield wastewater, which resulted from the high buffering capacity of the LDHs. The adsorption capacity increased as the adsorbents levels increased for the range studied. After treatment of the oilfield wastewater containing 30 mg L−1 of boron with Mg‐Al‐CO3‐LDHs, the final concentration of boron was within the discharge limit set by current Brazilian environmental legislation, which is 5 mg L−1. Pseudo–first‐order and pseudo–second‐order kinetic models were tested, and the latter was found to fit the experimental data better. Isotherms for boron adsorption by CLDHs were well described using the Langmuir and Freundlich equations.

Autothermal reforming of methane over nickel catalysts prepared from hydrotalcite-like compounds

Publisher Summary Autothermal reforming (ATR), a combination of steam reforming and partial oxidation reactions, is an advantageous route for syngas production for both economical and technical reasons. It has low-energy requirements because of the opposite contribution of the exothermic methane oxidation and endothermic steam reforming. The combination of these reactions can improve the reactor temperature control and reduce the formation of hot spots, thereby avoiding catalyst deactivation by sintering or carbon deposition. ATR allows the production of syngas with a wider range of H2/CO ratio by manipulating the relative concentrations of H2O and O2 in the feed. All these advantages indicate that ATR should be the technology of choice for large-scale GTL (gasto-liquid) plants. Supported metal catalysts have been used in the reforming reactions of hydrocarbons, and they are conventionally prepared by wet impregnation of different supports. This method is not fully reproducible and may give rise to some heterogeneity in the distribution of the metal on the surface. Fine metal particles tend to sinter at high temperature, resulting in the catalyst deactivation. This chapter describes nickel catalysts prepared from hydrotalcite-like compounds, with different Ni compositions, for the autothermal reforming of methane, comparing their performance with a conventional nickel-impregnated catalyst.

Solid-state Synthesis of La0.7Sr0.3MnO3 Powders using Different Grinding Times

Sr-doped lanthanum manganites (LSM) have been studied as promising materials for cathodes in solid oxide fuel cells (SOFC). In the present work La0.7Sr0.3MnO3 powders were synthesized by solid-state method evaluating the influence of dry or wet (using isopropanol) routes and different grinding times on the morphological and microstructural properties of LSM. The results of the synthesis of LSM powders pointed out that the use of solvent during homogenization results in poor crystallinity and only 6 hours of grinding at low speed in the ball mill is enough to obtain nano-sized crystalline phase by dry route. Scanning electron micrographs showed formation of agglomerates of fine primary particles. The electrical conductivity of the sintered LSM (La1xSrxMnO3, x= 0.2, 0.3 and 0.4) pellets with about 35% of porosity was measured by the two probe technique, showing a slight increase in the conductivity with strontium content.

Characterization of yttria-stabilized zirconia films deposited by dip-coating on La 0.7 Sr 0.3 MnO 3 substrate: Influence of synthesis parameters

Yttria-stabilized zirconia (YSZ, ZrO2-8%Y2O3) films were deposited onto lanthanum strontium manganite (LSM, La0.7Sr0.3MnO3) substrates using dip-coating process aiming for the application in solid oxide fuel cells (SOFCs). YSZ precursor was prepared by sol-gel method; three values of the organic/inorganic concentration ratio (1, 3 and 5) were utilized and the sol viscosity was adjusted (60 mPa·s and 100 mPa·s) before deposition on the substrate. The influence of these synthesis parameters on the structure and morphology of the deposited films was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The films showed characteristic peaks of LSM, YSZ (with cubic structure) and secondary phases of SrZrO3 and La2O3. Depending on the synthesis conditions, crack-free, homogeneous and well adhered films were obtained, with thickness of 11–24 μm.