Irma L. Botto

Anderson type heteropolyoxomolybdates in catalysis:: 1. (NH4)3[CoMo6O24H6]·7H2O/γ-Al2O3 as alternative of Co-Mo/γ-Al2O3 hydrotreating catalysts

A new preparation method of Co-Mo/γ-Al2O3 HDS catalyst has been developed by using the (NH4)3[CoMo6O24H6]·7H2O Anderson type heteropolyoxomolybdate supported on γ-Al2O3. The system can be considered as an interesting and simplified alternative to the traditional bimetallic catalyst. Diffuse reflectance spectroscopy measurements have been employed to confirm that the planar-arrangement of the heteropolyanion is not substantially altered by the adsorption process. The corresponding adsorption isotherm has been registered at room temperature due to the good solubility of the phase. In comparison with the traditional HDS catalysts, this new system shows the following relevant aspects: (a) the activity for the HDS of thiophene is similar in both cases, although the Co content is considerably lower than that of the impregnation of the ammonium heptamolybdate and cobalt nitrate hexahydrate solutions ([Co]/([Co]+[Mo])=0.14 in relation to 0.25–0.40 in the conventional system); (b) the phase adsorbs well onto the support; (c) the activity of molbydenum seems to be promoted by the presence of cobalt in the ordered distribution of the heteropolyanion on the surface of γ-Al2O3 (synergy-like effect). The primary structure of supported heteropolyoxomolybdate is clearly preserved; (d) whereas the conventional catalysts can be prepared through a series of steps (two impregnation operations, one for drying and another for the calcination at 550°C), the proposed method only requires one impregnation step and a drying step at 80°C, suppressing the calcination at 550°C.

IR spectra of VO2 and V2O3

Abstract IR spectra of the tetragonal modification of VO 2 and of the trigonal form of V 2 O 3 are recorded at room temperature and compared with that of V 2 O 5 . The investigated samples of the two lower-valent vanadium oxides, obtained on temperature-programmed reduction treatment, were also characterized with diffuse reflectance and electron-paramagnetic resonance spectra. The effect of atmospheric oxygen on these materials was revealed with XPS measurements and also studied with IR spectra.

(NH4)6[TeMo6O24] . 7H2O Anderson phase as precursor of the TeMo5O16 catalytic phase : thermal and spectroscopic studies

Abstract The thermal behaviour of the (NH 4 ) 6 [TeMo 6 O 24 ] · 7H 2 O Anderson phase has been analysed in N 2 and H 2 /N 2 atmospheres b differential thermal analysis and thermogravimetry (DTA-TG) and temperature-programmed reduction (TPR) techniques. X-ray diffraction, IR and Raman spectroscopies as well as scanning electron microscopy (including electron microprobe) have also been employed to characterize the intermediate and final products of the pyrolysis. Some studies on ammonium heptamolybdate, telluric acid, TeO 2 paratellurite and (NH 4 ) 3 [AlMo 6 O 24 H 6 ] · 7H 2 O Anderson phase have been carried out for comparative purposes. MoO 3 and TeO 2 are the solid products of the therm treatment in N 2 . The mild reducing effect of NH 3 decreases the temperature of the Te(VI) reduction. On the other hand, the TPR study permits the formation of the TeMo 5 O 16 , which is an interesting catalytic phase, to be established. Its stability range, between 400 and 500 °C, can be supported by the Mo(IV)-Te(IV) and Mo(VI)-Te 0 redox incompatibility. Mo 4 O 11 is the thermal product of the TeMo 5 O 16 decomposition, together with TeO 2 and MoO 3 according to the stoichiometry. However, some traces of MoO 2 induce the cyclic redox process, which makes it difficult to detect TeO 2 and MoO 3 . Likewise, Mo4O 11 shows a large range of stability (between 550 and 650 °C), unlike the thermal behaviour of other related molybdic phases.

Kristallographische Daten und IR-Spektrum von AlVO4

The unit cell parameters of AlVO4 have been determined from powder diagrams. The compound pertains to the triclinic system and is isostructural wi7h FeVO4. The infrared spectra of AlVO4 and FeVO4 and of a series of solid solutions in the system AlVO4/FeVO4 has also been recorded and discussed.

Anderson-type heteropolyoxomolybdates in catalysis: 2. EXAFS study on γ-Al2O3-supported Mo, Co and Ni sulfided phases as HDS catalysts

Abstract The nature of the Co (or Ni) and Mo sulfided species obtained starting from γ-Al 2 O 3 -supported Anderson heteropolyoxomolybdates (CoMo 6 and NiMo 6 ) has been analyzed by means of the extended X-ray absorption fine structure (EXAFS) technique with the aid of temperature-programmed reduction (TPR) and spectroscopic measurements. Results are discussed in relation to the adsorption isotherms and to the catalytic activity for the thiophene hydrodesulfurization (HDS) reaction. A comparison with traditional catalysts has been made.

Spectroscopical approach to some heteropolymolybdates with the anderson structure

Abstract The i.r. spectra of some phases with the Anderson structure of general formula ( NH 4 ) 3 [ XMo 6 O 24 H 6 ]7 H 2 O ( X = Al , Co , Cr , Fe and Ga ) have been reinvestigated. In addition, the Raman spectra have been also analyzed in an attempt to establish the correlation between the structural and vibrational properties. A study of the vibrational spectra of some other related phases has also been made for comparative purposes.

Characterization of a low-temperature form of InVO4

Abstract A low-temperature form of InVO4, belonging to the α-MnMoO4 structural type, was characterized. The unit cell parameters were determined from X-ray powder diagrams. The infrared spectrum was discussed with the aid of a “site-symmetry analysis.” The results were discussed in comparison with those of the corresponding high-temperature form (CrVO4 type) and with some other related compounds.

Vibrational Spectra of Arsenates and Phosphates of the Type Kcaln(XO4)2

Abstract The infrared and Raman spectra of polycrystal-line samples of different compounds of the types KCaLn(AsO4)2 and KCaLn(PO4)2, belonging to the hexagonal LaPO4, structural modification, were recorded and discussed. A complete vibrational assignment, based on a factor group analysis, is proposed. The influence of the different lanthanide cations on the internal vibrations of the XO4 groups is briefly discussed and some comparisons with related compounds are also made. It is well known that simple lanthanide arsenates, phosphates, vanadates and cnromates (V) of the type LnXO4 belong to two different structural types.

Reducibility and thermal behaviour of some Anderson phases

Abstract The thermal behaviour of the (NH 4 ) 3 [M(III)Mo 6 O 24 H 6 ] · 7H 2 O, Anderson phases, where M is Al, Co, Fe has been analysed in N 2 , N 2 /O 2 and N 2 /H 2 atmospheres using TG-DTA, TPR, and XRD techniques. Additional measurements were made by IR, EPR and Mossbauer spectroscopies, and also by scanning electron microscopy. Similar studies were carried out on ammonium heptamolybdate for comparative purposes. Molybdenum oxide and metallic molybdate are the solid products of the thermal treatment in N 2 and N 2 /O 2 atmospheres. While M 2 (MoO 4 ) 3 is observed when M is Al and Fe, the β-CoMoO 4 binary oxide is stabilized under both experimental conditions. The intermediate [(NH 4 ) 2 O] 0.8 MoO 3 (H 2 O) 0.3 phase is only observed when working in static air atmosphere at a very low heating rate. The temperature-programmed reduction (TPR) study permits the analysis of the different reduction steps of the Mo(VI) and M(III) is Fe, Co components. Mo 4 O 11 , MoO 2 , Mo and MMoO 4 (M is Co, Fe) are also observed. The formation of an Al-Mo reduced oxidic phase (related to MoO 2 ) can be inferred for the Al compound.

Das Schwingungsspektrum von Sr2V2O7 und die Schwingungseigenschaften des Divanadat-Ions

The infrared and laser-Raman spectra of Sr2V2O7 are reported and discussed by means of a “Site Symmetry” analysis. The principal force constants as well as the mean amplitudes of vibration for the V2O74− ion have been calculated using a simplified molecular model. Some aspects of the vibrational behaviour of the V−O−V bridge in this ion are also discussed.