CO oxidation and 4-nitrophenol reduction over ceria-promoted platinum nanoparticles impregnated with ZSM-5 zeolite

Abstract

Active new ceria-promoted platinum supported on ZSM-5 catalysts were prepared and characterized by X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), transform electron microscopy (TEM), temperature programmed desorption (TPD), and FTIR of CO adsorption. The samples were prepared by the incipient wetness impregnation method and calcined at 500 °C. The XRD patterns and FTIR spectra prove that the zeolite framework is kept unaltered after metal loadings. TEM images prove the presence of Pt nanoparticles with particle size starting from 14 to 27 nm. The FTIR data suggest the formation of Pt–O–Ce linkage. In-situ FTIR of CO adsorption over reduced samples proves the presence of Pt0 only, and no Ptn+–CO species are detected. The prepared catalysts were tested in both oxidation reaction (CO oxidation) in the gas phase and in reduction reaction (4-nitrophenol reduction) in the aqueous medium. Firstly, CO oxidation by O2 results in the formation of a CO2 peak at 2347 cm−1 as the only CO oxidation product in the studied frequency range. The intensity of the CO2 peak increases after the addition of Ce, and it is 4 times higher in Pt1Ce0.5ZSM-5 than that in the Ce-free sample. According to the FTIR data and previous reports, the increase in the catalytic activity may be due to the formation of Pt–O–Ce linkage. Secondly, Ce-promoted Pt1ZSM5 also exhibits enhanced catalytic activity towards the reduction of 4-nitrophenol to 4-aminophenol by NaBH4 in the aqueous medium. The first-order rate constant of the reduction increases ≈13 times after incorporating equal ratios of Pt and Ce (Pt1Ce1ZSM-5), and the activation energy (Ea) decreases to 40% of that in the reaction over Pt1ZSM-5.