D. MorontaCentro de Resonancia Magnetica, Escuela de F´ ´isica, Facultad de Ciencias, Universidad Central de Venezuela,Caracas, Apartado Postal 47586, 1041A, Venezuela,e-mail: dmoronta@fisica.ciens.ucv.ve.M. Mart´in-LandroveCentro de Resonancia Magnetica, Escuela de F´ ´isica, Facultad de Ciencias,Universidad Central de Venezuela and Instituto de Resonancia Magn´etica,La Florida-San Roman, Caracas, Venezuela´C. GagoCentro de Resonancia Magn´etica, Escuela de F ´isica,Facultad de Ciencias, Universidad Central de VenezuelaA.J.PardeyCentro de Equilibrios en Solucion, Escuela de Qu´ ´imica, Facultad de Ciencias,Universidad Central de Venezuela, Caracas, Venezuela

The formation of transition metal complexes between dichlorocopper(II) and a poly(4-vinylpyridine)/divinylbenzene(2%) polymeric matrix is described in this contribution. The nitrogen atom of the pyridine groups of the organic polymer is coordinatively bonded to the Cu center as suggested by X-ray photoelectron spectroscopy (XPS), UV–vis/diffuse reflectance (UV–vis/DR), electron paramagnetic resonance (EPR), differential scanning calorimetry (DSC) and Fourier transform infrared (FT-IR) techniques. The immobilized catalyst was also characterized by DTA-TGA analysis and the morphology and elemental analysis of this copper/poly(4-vinylpyridine) complex were studied by the scanning electron microscopy/energy dispersive X-ray (SEM/EDX) technique. This material catalyzes the water gas shift reaction as well as the reduction of nitrobenzene to aniline and azobenzene.

Vanadium nitride and carbide were synthesized by the temperature-programmed reaction of ammonium vanadate (NH4VO3) with pure NH3 and 20% CH4 in H2, respectively. Based on the XRD results, the catalysts showed VN and V8C7/V4C3 with an amount of V2O3 in the bulk after nitridation and carburization. The hydrogenation, hydrodesulfurization and hydrodenitrogenation reactions were studied and compared to vanadium sulfide catalyst. These catalysts (VC, VN) are stable under typical hydroprocessing conditions.

We have exposed the Polypropylene + virgin-High Density Polyethylene + woodflour and Polypropylene + recycled-High Density Polyethylene + woodflour composites under gamma irradiation to integral doses from 10 to 70 kGy at the constant dose rate of 4.8 kGy/h. ESR Spectroscopy was carry out. The nature of free radicals after two days of air storage induced by gamma irradiation is discussed. The peak to peak resonance line width, and his dependence with the integral dose on gamma irradiation, is discussed. The concentration radicals has been estimated for a group of singles lines, characterized by the same giromagnetic factor value, by direct numerical double integration.

Five perovskite oxides with the composition La1-x KxMnyFe1-yO3 (0 less than or equal to x, y less than or equal to 0.2) were synthesized by the co-precipitation method. Techniques such as chemical and XR fluorescence analysis, powder X-ray diffraction (XRD), BET surface area, IR, EPR and Mossbauer spectroscopy were applied to characterize the structural features of the perovskites. The activity of the solids was strongly dependent on the presence of iron carbides. It was observed that K promotes the reducibility of the solid to alpha-Fe giving rise to more carbide phases. Mn produces a significant increase in alkenes production. The combined presence of both K and Mn (La0.9K0.1Fe0.9Mn0.1O2.9) strongly modified the selectivity of the oxides, giving rise to a stable catalyst with high yield of C-2-C-4 alkenes. (C) 2002 Elsevier Science B.V. All rights reserved.

A study was carried out on the reaction of acetone transformation over bifunctional monometallic (Pt/H[Al]ZSM5, Sn/H[Al]ZSM5) and bimetallic (PtSn/H[Al]ZSM5) catalysts with variation of their tin atomic fraction (XSn=number of Sn moles/number of Sn moles + number of Pt moles). The solids prepared were analyzed by means of X-ray diffraction (XRD), nitrogen adsorption at −196°C, chemical analysis through inductive coupled plasma–atomic emission spectroscopy (ICP–AES) technique, energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), electronic paramagnetic resonance (EPR), transmission electronic microscopy (TEM), and by means of test reaction of toluene hydrogenation. Acetone transformation was carried out at 160°C, under atmosphere pressure, at an acetone/hydrogen molar ratio of 3 and varying WHSV. The results obtained show a sensitive variation in the catalytic properties as XSn is varied in the series of PtSn/H[Al]ZSM5 catalysts prepared; these changes are attributed to the presence of effects of the electronic and geometric type, which would be a consequence of the formation of a Pt–Sn alloy and probably of the phenomenon of decoration of platinum particles, which is evidenced from the evaluation of the solids by means of XPS and EPR.

The influence of the use of ethylenediamine in the preparation of iron–vanadium catalyst for toluene hydrogenation (HYD) and pyridine hydrodenitrogenation (HDN) has been studied. Both HYD and HDN activities increased significantly with Fe incorporation to vanadium sulphide and the beneficial effect of ethylenediamine was shown. Possible explanations for the enhancements in HYD and HDN conversion are discussed.

Electron spin resonance studies on polystyrene (PS), polypropylene (PP) and on 80/20 PS/PP blends with and without compatibilizer (block SBS), at 7.5wt%, irradiated with gamma rays from a 60Co source at a dose rate of 4.8kGy/h and at integral irradiation doses of 10, 25, 50, 60, 70, 400, 800 and 1300kGy in the presence of air and at room temperature are reported. Dependence of resonance line width, Hpp, resonance line shapes, K, and resonance line intensity, Ipp, on the integral dose of irradiation is investigated. Nature of free radicals after 10 days of air storage is discussed.

The preparation, characterization and catalytic properties of Rh2(CO)4Cl2 immobilized on poly(4-vinylpyridine) are reported. The polymer-immobilized Rh catalyst in contact with 80% aqueous 2-ethoxyethanol is active for the water gas shift reaction and nitrobenzene reduction to azoxybenzene under carbon monoxide at 100 °C. The polymer-immobilized Rh complex was found to be reusable. The Rh complex was coordinatively bonded to the pyridine groups of the organic polymer as suggested by UV–Vis/diffuse reflectance (UV–Vis/DR), Fourier transform infrared (FT-IR), and electron paramagnetic resonance (EPR) spectroscopies. The morphology and the elemental analysis of the immobilized catalyst were studied by scanning electron microscopy–energy dispersive X-ray (SEM–EDX) technique.

We report a study of the mechanical, thermal and morphological behaviour of blends of polypropylene filled with wood flour and sisal fibre (at 60/40 and 80/20 compositions, respectively), subjected to different doses of gamma irradiation (10, 25, 30, 50, 60 and 70 kGy), at room temperature and in the presence of oxygen. In addition, studies were carried out by infrared spectroscopy and electronic paramagnetic resonance to analyse the formation of radicals or functional groups influencing the behaviour of the irradiated compounds. Low irradiation doses improve the mechanical behaviour of the compounds under study (PP/wood flour, PP/sisal fibre). Thermal stability is acceptable and radical concentration in these materials is low. It was also demonstrated that it is possible to use low irradiation doses to modify the characteristics of PP and filler, which means a number of advantages: no chemical reagents are required and there are no residual polluting by-products or tedious post-treatment. Gamma-irradiation, therefore, is a promising technology to modify these composites in industry.

Catalysts for the selective reduction of nitrobenzene to aniline prepared from poly(4-vinylpyridine) (P(4-VP))-immobilized [Rh(COD)(amine)2](PF6) (COD=1,5-cyclooctadiene, amine=4-picoline, 3-picoline, 2-picoline, pyridine, 3,5-lutidine or 2,6-lutidine) complexes in contact with 80% aqueous 2-ethoxyethanol, 1×10−4 mol Rh/0.5 g of polymer, 0.9 atm of CO pressure at 100°C under water–gas shift reaction conditions (WGSR, CO+H2O⇄CO2+H2) are described. Aniline production (milimole/3 h) depends on the nature of the amine and decreases in the following order: 2-picoline (0.65)>4-picoline (0.59)≥3-picoline (0.56)>pyridine (0.49)>3,5-lutidine (0.38)>2,6-lutidine (0.34). The immobilized [Rh(COD)(2-picoline)2](PF6) complex was found to be reusable as a catalyst for the title reaction. The Rh/2-picoline complex was immobilized to the pyridine groups of the organic polymer as supported by Fourier transform infrared (FT-IR), electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), UV/Vis/diffuse reflectance (DR) spectroscopies, and scanning electron microscopy (SEM) studies.

The effect of temperature on the water–gas shift reaction, catalyzed by poly(4-vinylpyridine) immobilized [Rh(COD)(4-picoline)2]PF6 (COD=1,5-cyclooctadiene), has been studied under continuous-flow conditions at 100–180°C. The morphology of the immobilized catalyst was studied using a scanning electron microscope. The immobilized catalyst was also characterized by DTA–TGA analysis, FT-IR, UV–VIS reflectance, electron paramagnetic spectroscopy (EPR) and X-ray photoelectron spectroscopy (XPS), and surface area was determined by the BET method. The temperature dependence follows a segmented Arrhenius behavior. These results are discussed in terms of the possible presence of mono- and polynuclear-anchored rhodium species.

Homogeneous catalysis of the water-gas shift reaction has been accomplished by the use of solutions of CuCl2 · 2H2O in aqueous pyridine and other substituted pyridine (methyl pyridines or dimethylpyridine) solutions. This system is stable, low active catalyst displaying turnover frequencies for hydrogen production (TF(H2)) of about 6 moles H2 per mole Cu per day for [Cu] = 20 mM, P(CO) = 1.9 atm and T = 120°C.

A series of substituted AlPO4 molecular sieves with the AEL topology were prepared and characterized by different techniques, to evaluate the amount and nature of the additional elements and their effect on the acidity and catalytic properties of the resulting solids. It was found that a one-to-one interaction between Lewis (L) and Brønsted (B) sites occurs after calcination of the substituted materials, leading to an enhanced acidity and causing, as a result, an increase in the selectivity towards isobutene during the transformation of 1-butene. Substitution models are discussed in order to rationalise the origin and nature of such B-L synergism.

[Cr-x,Al-y] silicates with MFI-type structure were synthesized from synthesis gels with a Si/(Cr+Al) molar ratio of 23, and compositions of chromium and aluminum varying from 0 to 4. The solids were characterized by chemical analysis, XRD, infrared spectroscopy, magic angle spinning n.m.r., SEM-TEM, N-2 adsorption, and e.s.r. Ail solids were highly crystalline materials. The e.s.r. study shows the presence of Cr(III) in different magnetic environments, depending upon the treatments of the samples. Extensive oxidation of occluded Cr(lll) clusters to Cr(VI) species occurred after calcination, whereas the presence of structural and nonstructural Cr(V) species was also detected. It was observed that the presence of chromium ions in the synthesis gel increases the amount of structural aluminum in the zeolites, which produces [Cr,Al] silicates with acidity and activity in the n-heptane cracking reaction, higher than conventional Al silicates. (C) Elsevier Science Inc. 1997.

Two series of iron-pentasil molecular sieve catalysts were synthesized. One series consisted of H-ZSM-5 type zeolites with different silicon/aluminium ratios impregnated with ferric nitrate, and the other included ferrisilicates with different silicon/iron ratios. The catalytic tests on syngas conversion were effected at 0.7–2.1 MPa at between 240–300° C in a flow system with a fixed bed reactor. The characterization of the solids shows that in the impregnated series, the iron was transformed into α-iron and carbide phases by means of treatment with hydrogen, carbon monoxide and by the effect of the syngas under the reaction conditions. On the other hand, in the ferrisilicate series, the iron retains the ionic form [iron (III)-iron (II) ], regardless of the treatment, thereby indicating its incorporation into the structure of the solid. The catalytic behaviour of both series also differs. The solids produced by impregnation were seen to produce mostly hydrocarbons in the petrol range with the expected selectivity properties, whereas the ferrisilicates were selective towards the formation of i-C4.

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