2 research outputs found
Preparation of iron molybdate catalysts for methanol to formaldehyde oxidation based on ammonium molybdoferrate(II) precursor
It was demonstrated that iron molybdate catalysts for methanol oxidation can be prepared
using Fe(II) as a precursor instead of Fe(III). This would allow for reduction of acidity of
preparation solutions as well as elimination of Fe(III) oxide impurities which are detrimental for
the process selectivity. The system containing Fe(II) and Mo(VI) species in aqueous solution was
investigated using UV–Vis spectroscopy. It was demonstrated that three types of chemical reactions
occur in the Fe(II)–Mo(VI) system: (i) formation of complexes between Fe(II) and molybdate(VI)
ions, (ii) inner sphere oxidation of coordinated Fe(II) by Mo(VI) and (iii) decomposition of the
Fe–Mo complexes to form scarcely soluble Fe(III) molybdate, Mo(VI) hydrous trioxide and
molybdenum blue. Solid molybdoferrate(II) prepared by interaction of Fe(II) and Mo(VI) in
solution was characterized by EDXA, TGA, DTA and XRD and a scheme of its thermal evolution
proposed. The iron molybdate catalyst prepared from Fe(II) precursor was tested in methanol-toformaldehyde
oxidation in a continuous flow fixed-bed reactor to show similar activity and
selectivity to the conventional catalyst prepared with the use of Fe(III)
Peroxide-based route for the synthesis of zinc titanate powder
In this work the thermodynamical solubility diagrams of zinc and titanium hydroxides
were reviewed in order to determine the conditions for maximum degree of phase composition
homogenization of precipitates. Experimental investigation of dependency of titanium peroxohydroxide
solubility on solution acidity has been carried out and coprecipitation of zinc ions has been
studied. It was concluded that precipitation by constant addition of mixed salts and base solutions
into the mother liquor with constant acidity of pH 8.5 allows maximizing homogenization of
precipitate composition. Thermal treatment process of mixed zinc and titanium hydroxides
coprecipitated with hydrogen peroxide was studied using thermogravimetric analysis, differential
thermal analysis and X-ray diffraction methods. It was found that precipitates of co-precipitated
mixtures of zinc and titanium hydroxides contained impurities of salts precursors of the Zn
(NO3)2 and TiOCl2 at a level of 1%. The experimental data demonstrate the influence of hydrogen
peroxide on crystal growth rate of the zinc titanate during thermal treatment. The temperature
ranges and kinetic parameters of hydroxide mixture dehydration, decomposition of the titanium
peroxohydroxide and precursor impurities were determined