Abstract

ARTEAGA, Geomar et al. Effects of the thermal treatments on dispersion, reducibility and activity of Ni/Al₂O₃ and Ni-Sn/Al₂O₃ catalysts. Rev. Téc. Ing. Univ. Zulia [online]. 2002, vol.25, n.1, pp.33-41. ISSN 0254-0770.

    Effects of the calcination and oxychlorination on cyclohexane dehydrogenation activity of Ni/Al₂O₃ and Ni-SnAl₂O₃ catalysts were studied. Four Cl-free catalysts were prepared, two monometallic catalysts with 1.0 and 5.0% Ni by impregnation, and two bimetallic catalysts with 1.0%Ni-0.5%Sn and 5.0%Ni-2.5%Sn by step impregnation, both with Sn/Ni atomic ratio = 0.25. Calcination (in air) and oxychlorination (in air + CHCl₃) treatments were carried out at 500°C for 1 h. The catalysts were characterized by temperature-programmed reduction (TPR), CO chemisorption at 22°C and oxygen titration at 400°C. The reaction was performed using a flow reactor at 300°C. All the catalysts presented very low Ni dispersions. The thermal treatments, particularly the oxychlorination, caused a decrease in the dispersion and variations in the degree of reduction. These effects were dependent on the Ni content and the presence of Sn. The TPR profiles suggest the formation of bimetallic particles of Ni and Sn in the 5.0Ni-2.5Sn catalyst subjected to calcination or oxychlorination. This catalyst showed a low activity, which was independent of the treatment. For the remaining catalysts, the oxychlorination produced more active catalysts than the calcination. Electronic effects of Sn on Ni explain the lower activity of bimetallic ensembles.

Keywords : Calcination; oxychlorination; Ni/Al₂O₃ catalysts; Ni-SnAl₂O₃ catalysts; dehydrogenation.