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Résumé :
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Phosphorus (P) modified H-ZSM-5 catalysts were prepared by wet impregnation method by varying P loadings from 0 to 7.43 wt % using phosphoric acid (H3PO4) as the P source. The catalysts were tested for ethanol dehydration in the temperature range of 523—723 K. The P-modified catalysts were found to be highly active and selective toward ethylene at 673 K and atmospheric pressure. In addition, the P-modified catalysts were found to be extremely stable more than 200 h without any sign of deactivation. However, the selectivity was found to be strongly dependent on several factors such as P content, reaction temperature, and space velocity (WHSV). The P-modified ZSM-5 catalysts were also found to be highly active for the dehydration of aqueous ethanol solutions (10 wt %) showing very high ethylene selectivity (above 98%) at significantly lower temperature 623 K. The catalysts were thoroughly characterized using various methods, including N2 physisorption, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric differential thermal analysis (TG-DTA), 1H, 27Al, and 31P magic angle spinning nuclear magnetic resonance (MAS NMR), and amonia temperature programmed desorption (NH3-TPD). 27Al MAS NMR spectra suggest that P addition facilitate the breaking of Si―O―Al bond that lead to a partial dealumination. NH3-TPD results indicate that total acidity as well as density of high strength acid sites were decreased with P loading.
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