Oxidação preferencial de CO em catalisadores à base de ouro : estudo do efeito do suporte e do método de síntese do catalisador
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Data
2016-03-29Autor
Miranda, Aline Rodrigues Lopes
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The CO preferential oxidation reaction (PROX) is used in the purification of hydrogen
streams for various applications. Since the discovery of improved catalytic properties
of gold particles, at nanometer range, in the CO oxidation reaction at low temperature,
Au catalysts have been the subject of numerous investigations of CO oxidation and
PROX. Concerning the heterogeneous catalysis, the catalyst activity is determined by
several factors: the nanoparticles size, the metal loading and dispersion, the nature
and porosity of the support, and the metal/support interaction. To understand the
dependence of the support and the influence of the synthesizing method on the
material properties and catalytic performances, gold nanoparticles supported on three
different oxides (CeO2, MnO2 and TiO2) were successfully synthesized by the
deposition precipitation (DP) method, using urea, and modified polyol (MP) method,
using PVP as surfactant and sodium borohydride as reducing agent. Additionally,
Au/SiO2 was obtained by the DP method. Characterizations were performed to assess
the crystallinity, the metal mass percentage, the reduction temperatures and the
respective reducing gas consumptions of pure oxides and supported materials
synthesized by both methods. In addition, microscopic pictures were obtained to
evaluate the materials morphology and the gold nanoparticles diameter. The Au
catalysts synthesized by the DP method presented smaller particle sizes as compared
to catalysts obtained by the MP method. Catalytic evaluation of the CO oxidation and
PROX reactions were performed using temperature ramp starting at room temperature
up to 200 °C. As a comparative parameter, the ratio between the catalyst mass and
the gas feed flow remained constant at 1 mg / 1 mL / min for all reactions. The results
showed that Au supported on TiO2 prepared by the DP method presented complete
CO conversion at room temperature, but with the simultaneous supply of H2, this
catalyst tends to oxidize H2, decreasing the CO conversion activity. On the other hand,
the Au/CeO2 catalyst prepared by the DP method presented activity up to about 200
°C for PROX and better selectivity towards the CO2 formation.