Robinson L. Manfro

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.

Combined DFT and experimental study of the dispersion and interaction of copper species in Ni-CeO2 nanosized solid solutions

Nanosized nickel (Ni) and copper (Cu) doped ceria (CeO2) have attracted attention as solid solutions for energy- and environment-related applications. Furthermore they present an interesting combination of thermal and chemical stability and catalytic activity in technologically important reactions like water gas shift, ethanol reforming, hydrogenation, among others. In contrast, not much is known about the key-factors that govern the formation and the nature of the atomic structure of these materials. This study investigated with the help of the density functional theory (DFT) and experimental methodologies the formation of ceria-based solid solutions in the presence of Ni and Cu species. The materials were prepared by the incipient wetness impregnation and subsequently characterized by various experimental techniques (XPS, Raman, XRD, XRF, HR-TEM), while the electronic structures have been investigated by using DFT calculations with Hubbard corrections (DFT+U method). Theoretical calculations and experimental studies suggest that Ni species are able to form a solid solution by isomorphic substitution of bulk Ce atoms, however it was found a limit after which saturation is reached and therefore the addition of extra Ni atoms do not affect the crystal structure of the solid solution. Consequently, the formation of surface domains of nickel oxide (NiO) phases is expected. According to our findings the addition of small amounts of Cu can neither disturb the bulk structure nor force the incorporation of Cu atoms and therefore Cu species are also expected to segregated oxide (CuO). Our theoretical approach is consistent with the experimental data and we could identify an idealized solid solution structure that presents a close similarity with the experimental findings. From this theoretical structure, an interaction of the type Ni–Ni pair was identified. Our theoretical studies have predicted lattice contraction as a function of the Ni loading. From an energetic point of view we show that small amounts of Ni are easily incorporated whereas by raising Ni concentration and by adding Cu a sharp increase of the formation energy is observed. High formation energies along with strong lattice contractions was associated as plausible causes for the segregation of both Ni and Cu oxides and have been suggested as simple indicators of key factors for tailoring doped oxides containing controlled dopant concentrations.