Hydrotalcite-like compounds containing transition metals as solid base catalysts for transesterification

Hydrotalcite-like compounds (HTLCs) containing Mg2+, Ni2+ and Al3+ layered double hydroxide (LDH) were synthesized by co-precipitation method and calcined at 773 K for 10 h performed as heterogeneous base catalysts for transesterification of soybean oil with methanol to produce biodiesel. These four different MgAlNi catalysts were characterized by nitrogen physisorption, X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), temperature programmed desorption with CO2 (CO2-TPD), nitrogen adsorption-desorption. The Mg/Ni molar ratio varies over the range from 4 to 16 of the MgAlNi catalysts at a constant Al ratio in the hydrotalcite-like structures. The conversion of FAME was related to the basicity and Mg content of the MgAlNi catalysts, with MgAlNi 16 showing the highest basicity, and the lowest surface area due to Mg2+-O2− and Al3+-O2− pairs. The optimum conditions were obtained with a methanol/oil molar ratio of 21, 0.3% catalyst (w/w, oil), and 1200 rpm stirring speed for 4 h at 338 K, which results in the highest FAME conversion of 87%

Effect of water vapour on the molecular structures of supported vanadium oxide catalysts at elevated temperatures

The effect of water vapor on the molecular structures of V2O3-supported catalysts (SiO2, Al2o3, TiO2, and CeO2) was investigated by in situ Raman spectroscopy as a function of temperature (from 500°C to 120°C). Under dry conditions only isolated surface VO4 species are present on the dehydrated SiO2 surface, and multiple surface vanadium oxide species (isolated VO4 species and polymeric vanadate species) are present on the dehydrated Al2O3, TiO2, and CeO2 surfaces. The raman Features of the surface vanadium oxide species on the SiO2 support are not affected by the introduction of water vapor due to the hydrophobic nature of the SiO2 support employed in this investigation. However, the presence of water has a pronounced effect on the molecular structures of the surface vanadium oxide species on the Al2O3, TiO2, and CeO2 supports. The Raman band of the terminal V-O bond of the surface vanadia specieson these oxide supports shifts to lower wavenumbers by 5-30 cm^-1 and becomes broad upon exposure to moisture. Above 230°C, the small Raman shift of the surface vanadium oxide species in the presence of water suggests that the dehydrated surface VOx species form a hydrogen bond with some of the absorbed moisture. Upon further decreasing the temperature below 230°C, the hydrogen-bonded surface VOx species are extensively solvated by water molecules and form a hydrated surface vanadate structure (e.g. decavanadate). The broad Raman band at ± 900 cm^-1, which is characteristic of the polymeric V-O-V functionality, appears to be minimally influenced by the presence of water vapor and is a consequence of the broadness of this band. Oxygen-18 isotopic labeling studies revealed that both the terminal V=O and bridging V-O-V bonds readily undergo oxygen exchange with water vapor. The current observations account for the inhibiting effect of moisture upon oxidation reactions over supported metal oxide catalysts and are critical for interpreting in situ Raman during hydrocarbon oxidation reactions where H2O is a reaction product

Photocatalytic activity of the (NH4)(2)V6O16/g-C3N4 composite catalysts for water splitting applications

A hydrothermal method was used to prepare a lozence shape like (NH4)2V6O16 photocatalyst to split water into hydrogen. The energy gap of the (NH4)2V6O16 is about 2.7ev and the absorption wavelength is about 350–800 nm. In order to modify and enhance the photocatalytic reactivity of the (NH4)2V6O16, a graphitic carbon nitride (g-C3N4) possessing higher of lone pairs that can excite electron to combine with H+ and decrease electron-electronic hole recombination was added into the lozence shape like (NH4)2V6O16 to form a composite material. Thus, the synsthesis of the lozence shape like (NH4)2V6O16/g-C3N4 photocatalysts were controlled by the pH value, hydrothermal temperature, and the g-C3N4 concentration. For the photocatalytic reactivity of catalysts, a self-assemble reactor equipped with GC-TCD is used to analyze the water splitting efficiency. The optimum conditions to synthesize pure (NH4)2V6O16 are the acidic environment of pH = 3, the hydrothermal temperature of 200 °C, and the hydrothermal time of 4 h. The optimum concentration of g-C3N4 in the (NH4)2V6O16/g-C3N4 composite is 14 wt% and the accumulative concentration of hydrogen production reaches to the highest value of 2300 μmol/g cat

The formation of (NH4)2V6O16 phase in the synthesized InVO4 for the hydrogen evolving applications

By controlling the synthesized conditions such as the compositions, pH and hydrothermal temperature of the In (or NH4)-V-O compounds, the structural information have been determined with the potential application in the hydrogen evolving efficiency. When the addition of ammonium ions to adjust the pH with the hydrothermal time of 4 h, there is a maximum hydrogen production of 140.8 μmol/g·cat. The maximum hydrogen production reaches at pH of 5. In addition, the (NH4)2V6O16 phase in the synthesized InVO4 has been observed. This crystalline ammonia vanadium-based material is capable to perform the photocatalysis process in hydrogen evolving

Preparation and characterization of hydrotalcite-like compounds containing transition metal as a solid base catalyst for the transesterification

Hydrotalcite-like compounds (HTLCs) containing Mg2+, Fe3+ and Al3+ layered double hydroxide (LDH) were synthesized by co-precipitation method and calcined at 873 K for 16 h. These heterogeneous base catalysts were used for the transesterification of soybean oil with methanol to produce biodiesel. The Mg/Fe molar ratio was varied from 6 to 15, but the MgAlFe catalysts have a constant Al composition in the hydrotalcite-like structures. The catalysts were characterized by nitrogen physisorption, X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), CO2 temperature programmed desorption (CO2- TPD), field-emission scanning electron microscope (FE-SEM), and Fourier transfer infrared spectroscopy (FTIR). The conversion of fatty acid methyl ester (FAME) has been affected by the basicity and Mg content in the MgAlFe catalysts. When MgAlFe 15 was used, the highest basicity and high conversion of FAME (81%) was obtained due to the formation of Mg2+–O2−, Al3+–O2− pairs, and the higher CO2-desorption temperature

Photocatalytic H₂ Generation Efficiencies of TiO₂ Nanotube-based Heterostructures Grafted with ZnO Nanorods, Ag Nanoparticles, or Pd Nanodendrites

TiO₂ nanotube-based heterostructures grafted with ZnO nanorods, Ag nanoparticles, or Pd nanodendrites were synthesized for photocatalytic H₂O/CH₃OH splitting and H₂ generation. Compared with P25 TiO₂ nanoparticles and bare TiO₂ nanotubes, these heterostructures, in particular, the one grafted with Pd nanodendrites, were found to present a markedly enhanced photocatalytic H₂ generation efficiency (net H₂ generation rate ∼143 μmol/h). Rather than the surface area of the photocatalysts, the lifetime (separation) of photogenerated carriers and, in particular, the surface plasmon resonance-stimulated carrier excitation dominated the number of total effective carriers. A power relationship with an exponent of 0.2 between the H₂ generation rate and the number of total photogenerated carriers was determined, which suggests that the number of effective carriers or the efficiency in H₂O/CH₃OH splitting might decay in an exponential way