Effect of catalyst preparation on Au/Ce1−xZrxO2 and Au–Cu/Ce1−xZrxO2 for steam reforming of methanol

We tested 3 wt% gold (Au) catalysts on CeO₂–ZrO₂ mixed oxides, prepared by co-precipitation (CP) and the sol–gel (SG) technique, for steam reforming of methanol (SRM). Uniform Ce_1−xZr_xO₂ solid solution was dependent on the Zr/Ce ratio, where the incorporation of Zr⁴⁺ into the Ce⁴⁺ lattice with a ratio of 0.25 resulted in smaller ceria crystallites and better reducibility, and was found to be efficient for SRM activity. The catalytic activity was suppressed when the ratio was ≥0.5, which led to the segregation of Zr from solid solution and sintering of Au nanoparticles. It was found that the CP technique produced better catalysts than SG in this case. For the bimetallic catalysts, the co-operation of Au–Cu supported on Ce_0.75Zr_0.25O₂ (CP) exhibited superior activities with complete methanol conversion and low CO concentration at 350 °C. Furthermore, the size of the alloy particle was strongly dependent on the pH level during preparation.     

Electrolytic admicellar polymerization of pyrrole on natural rubber/clay nanocomposites

Organic–inorganic composites consisting of natural rubber (NR), polypyrrole (PPy), and sodium montmorillonite (Na‐MMT) were synthesized via electrolytic admicellar polymerization. A constant potential of 9 volts was chosen for the synthesis. The PPy concentration was fixed at 100 mM, and the clay contents were varied from 1 to 7 parts per hundred of rubber (phr). The synthesized nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy (TEM), together with thermal stability (TGA), mechanical properties, and electrical conductivity (σ_dc) studies. The FTIR spectra indicated the characteristic peaks of both PPy and MMT clay and also evidenced a slight interaction between the PPy chain and the clay layers, verifying the success of electrolytic admicellar polymerization. XRD and TEM results pointed out the good dispersion of clay platelets in the polymer matrix, suggesting an exfoliated structure. The morphology of the nanocomposites was greatly dependent on the amount of MMT clay, especially at a 7 phr loading. The initial modulus and tensile strength of the nanocomposites containing the 7 phr loading were about four and two times higher, compared with unfilled NR/PPy, respectively. Thermal stability studies revealed a slight improvement in the decomposition temperature for the PPy component by the clay layers, whereas the opposite trend was found for the NR component. More interestingly, the electrical conductivity of the admicelled rubber increased significantly (～ 19–32 times) with increasing clay contents from 1 to 7 phr, in comparison with unfilled NR/PPy. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fabrication and characterization of new semiconducting nanomaterials composed of natural layered silicates (Na-MMT), natural rubber (NR), and polypyrrole (PPy)

An electrolytic admicellar polymerization was chosen for synthesizing new semiconducting nanomaterials composed of sodium montmorillonite (Na⁺-MMT), polypyrrole (PPy), and natural rubber (NR). The contents of the pyrrole monomer and the Na⁺-MMT were varied from 100 to 800 mM and 1-7 parts per hundred of rubber (phr), respectively. Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM) were used to confirm the success of the synthesis. The morphological studies carried out by X-ray diffraction (XRD) and TEM pointed out the different states of dispersion of the layered silicates, whereas the study done by scanning electron microscopy (SEM) showed a great dependence of the nanocomposite morphology on the inclusion of the layered silicates. Thermal stability studies demonstrated the thermo-protecting and thermo-oxidative behaviors imparted by the layered silicates. The mechanical and DC electrical conductivity properties were significantly improved with the inclusion of the layered silicates, especially at a 7 phr loading.     

Effect of support composition and metal loading on Au catalyst activity in steam reforming of methanol

Gold (Au) supported on CeO₂–Fe₂O₃ catalysts prepared by the deposition-coprecipitation technique were investigated for steam reforming of methanol (SRM). The 3 wt% Au/CeO₂–Fe₂O₃ sample calcined at 400 °C achieved 100% methanol conversion and 74% hydrogen yield due to a strong Ce–Fe interaction in the active solid solution phase, Ce_xFe_1−xO₂. The sintering of Au particles was observed when the highest metal content of 5 wt% was registered, which worsened the SRM activity. According to the TPR and TPO analysis, it was found that the transformation of the α-Fe₂O₃ structure in the mixed oxides and the coke deposition were the main factors for the rapid deactivation of the catalyst.