III International Conference

PP-II-91The properties of the samples were characterized by BET surface area measurement,transmission electron microscopy (TEM), X-ray powder diffraction (XRD), thermoprogrammedreduction with H 2 (TPR-H 2 ), thermo-programmed desorption of NH 3 (TPD-NH 3 ) and IR-spectroscopy.The surface area of MoO 3 -Al 2 O 3 systems obtained by sol–gel synthesis was slightlyhigher than for commercial Al 2 O 3 , while pore size and pore volume was lower. The Moprecursor introduction into the sol after it peptization (Pt/MoO 3 -Al 2 O 3 -2 sample) led to moreuniform pore size distribution than in the case of addition before peptization (Pt/MoO 3 -Al 2 O 3 -1 sample).The XRD data demonstrated that after sol-gel synthesis the MoO 3 particles werepractically invisible in XRD spectra indicating rather small size of the particle or the presenceof amorphous phase of molybdena. Note, that for impregnated samples the signals of MoO 3phase were well detected by XRD analysis.The Pt/MoO 3 -Al 2 O 3 -2 sample has comparable activity with the impregnated catalysts, butthe stability in time-on-stream is much higher for sol-gel synthesized catalyst. In contrast, thePt/MoO 3 -Al 2 O 3 -1 sample was inactive in toluene hydrogenation reaction.To study sulfur tolerance of the Pt/Al 2 O 3 catalysts, H 2 S was added to the feed by thepulse injection of H 2 S+N 2 mixture. The amount of H 2 S needed for complete deactivation ofPt/MoO 3 -Al 2 O 3 -2 system prepared by sol-gel method was in 5 times higher than forconventional impregnated Pt/MoO 3 /Al 2 O 3 catalyst.References1. Mizushima, Y., and Hori, M., Appl. Catal. 88, 137 (1992).2. Balakrishnan, K., and Gonzalez, R. D., J. Catal. 144, 395 (1993).3. G.M. Pajonk, Appl. Catal. 72 (1991) 217-266.4. Zou,W., and Gonzalez, R. D., Appl. Catal. 102, 181 (1993).5. Lopez, T., Herrera, L., Gomez, R., Zou, W., Robinson, K., and Gonzalez, R. D., J. Catal. 136,621 (1992).328