Jesús E. Sueiras

Different morphologies of silver nanoparticles as catalysts for the selective oxidation of styrene in the gas phase

Silver nanoparticles of different morphologies were prepared using the polyol process and then dispersed on alpha-alumina. Catalysts were tested for the selective oxidation of styrene in the gas phase. Activity and selectivity were strongly dependent on the morphology of the silver nanoparticles.

Supported choline hydroxide (ionic liquid) as heterogeneous catalyst for aldol condensation reactions

Choline hydroxide was used as a basic catalyst for aldol condensation reactions to produce new C-C bonds between several ketones and aldehydes. Choline supported on MgO exhibits higher TOF values than other well known basic catalysts in these reactions.

Nanoplatelet-based reconstructed hydrotalcites: towards more efficient solid base catalysts in aldol condensations

Rehydration of Mg-Al hydrotalcite in the liquid phase using ultrasounds or a high stirring speed leads to nanoplatelets with surface areas of 400 m(2) g(-1), displaying catalytic activities in aldol condensations up to 8 times higher than the best catalytic system reported in the literature.

Comparative study of the morphology and surface properties of nickel oxide prepared from different precursors

Abstract Several NiO samples were prepared from different nickel precursors: nickel nitrate hexahydrate, nickel acetate tetrahydrate and nickel hydroxide. All samples were characterized using BET, X-ray diffraction (XRD), temperature-programmed reduction (TPR) and scanning electron microscopy (SEM) techniques. The results showed that a careful decomposition of nickel nitrate hexahydrate until formation of Ni3(NO3)2(OH)4 and subsequently calcination of this intermediate to form NiO led to very homogeneous octahedral NiO particles. Particle size can be controlled by means of the calcination temperature (around 200 nm for 400 °C during 4 h and 100 nm for 350 °C during 20 min). NiO obtained from nickel hydroxide is more amorphous with high specific surface area (161 m2/g) and sponge-like aspect. When nickel acetate tetrahydrate is calcined, metallic nickel is obtained together with the expected NiO phase. These samples showed different morphologies than the other prepared NiO.

Study of preparation conditions of NiO–MgO systems to control the morphology and particle size of the NiO phase

Several NiO–MgO samples were prepared from nickel nitrate hexahydrate and different sources of magnesia by using a NiO/MgO weight ratio of 1:1 and 4:1 and two different preparative paths. All the samples were structurally characterized using BET, XRD, SEM and TPR techniques. The results showed that the sequence of decomposition of the Ni(NO3)2·6H2O–MgO systems is similar to the sequence reported for the nickel nitrate hexahydrate without magnesia. XRD identified complete solid solutions for all the NiO–MgO systems prepared. Their BET areas were similar but their different morphologies and particle sizes mainly depended on the preparative path. Independently of the magnesia used, the NiO–MgO systems prepared by controlled decomposition of the nickel nitrate hexahydrate until Ni3(NO3)2(OH)4 was formed and which were subsequently calcined to form NiO (path B) led to very homogeneous particles of sizes around 100 nm. Path B also gave the highest degrees of NiO reduction.

Characterization of potassium-doped nickel catalysts and activity for selective hydrogenation of 1,6-hexanedinitrile

Abstract Studies of the chemical preparation, BET surface areas, X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), temperature-programmed reduction (TPR) and catalytic activities of several nickel catalysts were carried out for the catalytic hydrogenation of adiponitrile, in a continuous process at 1 atm pressure, 443 K, and in the absence of ammonia. Surface areas decrease with NiO reduction temperature. XRD, XPS and TPR measurements detect NiO incipient reduction at 473–498 K, a NiO reducibility inhibitor character for potassium, and 99.9% reduction degrees above 573 K. Selectivities of 100% with respect to 6-aminohexanenitrile are obtained at 60% conversion for catalysts with potassium contents of 10.5 × 10 −4 g K 2 O/g Ni.

Surface characterization and catalytic properties of several graphite supported potassium-free and potassium-doped nickel catalysts

Abstract Studies of the chemical preparation, activation energies of reduction by temperature-programmed reduction. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and catalytic activities of several graphite supported potassium-free and -doped nickel catalysts were carried out for the catalytic hydrogenation of 1,6-hexanedinitrile in a continuous process at 1 atm pressure, 443K, and in the absence of ammonia. Activation energies of reduction for the graphite supported non-stoichiometric NiO were higher than those from the unsupported non-stoichiometric NiO. Increasing potassium contents increase the activation energies of reduction. XRD measurements showed the presence of graphite, NiO and Ni phases, and also the loss of graphite due to gasification at temperatures higher than ca. 723 K. XPS showed the surface crystalline phases present and indicated the inhibiting effects of graphite and potassium upon the reducibility of NiO, the metallic nickel sintering and the graphite gasification at high temperatures. The catalytic conversions increase at higher NiO reduction degrees, potassium drives selectivity towards 6-aminohexanenitrile, and as graphite prevents metallic nickel from sintering, conversions remain high at temperatures of 723 K. 100% Selectivities with respect to 6-aminohexanenitrile were obtained at conversions higher than 50% for catalysts with potassium contents of 1.4·10−3 g K2O/g catalyst and 0.21 g Ni/g graphite. A mechanism is proposed.

Structural characteristics and catalytic performance of nickel catalysts for selective hydrogenation of 1,6-hexanedinitrile

Abstract Several nickel catalysts have been characterized on the basis of their Brunauer—Emmett—Teller (BET) surface areas, X-ray diffraction, X-ray photoelectron spectra, field-emission scanning electron microscopy and temperature-programmed reduction properties. The catalysts were used for the heterogeneous hydrogenation of 1, 6-hexanedinitrile at 443 K and atmospheric pressure, with no ammonia in the feed. Highly reduced nickel with a low BET area is obtained above 498 K. XPS and field-emission scanning electron micrographs of reduced catalysts revealed the appearance of incipiently reduced nickel on top of NiO crystals at 463–473 K. This structure is responsible for the high hydrogenation activity: however, only 100% selectivities toward 6-aminohexanenitrile were obtained by reduction at temperatures as high as 623–673 K. It seems that a specific arrangement of nickel atoms is required to obtain selective catalysts.

Biohydrogen production by dark fermentation of glycerol using Enterobacter and Citrobacter Sp

Glycerol is an attractive substrate for biohydrogen production because, in theory, it can produce 3 mol of hydrogen per mol of glycerol. Moreover, glycerol is produced in substantial amounts as a byproduct of producing biodiesel, the demand for which has increased in recent years. Therefore, hydrogen production from glycerol was studied by dark fermentation using three strains of bacteria: namely, Enterobacter spH1, Enterobacter spH2, and Citrobacter freundii H3 and a mixture thereof (1:1:1). It was found that, when an initial concentration of 20 g/L of glycerol was used, all three strains and their mixture produced substantial amounts of hydrogen ranging from 2400 to 3500 mL/L, being highest for C. freundii H3 (3547 mL/L) and Enterobacter spH1 (3506 mL/L). The main nongaseous fermentation products were ethanol and acetate, albeit in different ratios. For Enterobacter spH1, Enterobacter spH2, C. freundii H3, and the mixture (1:1:1), the ethanol yields (in mol EtOH/mol glycerol consumed) were 0.96, 0.67, 0.31, and 0.66, respectively. Compared to the individual strains, the mixture (1:1:1) did not show a significantly higher hydrogen level, indicating that there was no synergistic effect. Enterobacter spH1 was selected for further investigation because of its higher yield of hydrogen and ethanol.

Simultaneous in situ generation of hydrogen peroxide and Fenton reaction over Pd–Fe catalysts

High mineralization degree of organic compounds can be achieved by a novel environmentally-friendly full heterogeneous Pd-Fe catalytic system, which involves in situ generation of hydrogen peroxide from formic acid and oxygen, and oxidation of organic compounds by Fenton process in a one-pot reaction.