Applied Surface Science, Vol.378, 489-495, 2016
Effect of modification methods on the surface properties and n-butane isomerization performance of La/Ni-promoted SO42-/ZrO2-Al2O3
The La and/or Ni was introduced into alumina-promoted sulfated zirconia by impregnation and co-precipitation to improve the catalytic property of n-butane isomerization. Catalysts characterization shows that the addition of La/Ni has a remarkable influence on the surface and textual properties depending on the modification method. The impregnation of La/Ni facilitates the transformation of a small amount of tetragonal zirconia into monoclinic phase, while the co-precipitation improves the stability of tetragonal ZrO2. H-2-TPR indicates that the addition of La/Ni changes the interaction between SO42- and supports, which affects the acidity on the surface. Specifically, the Lewis acidity is significantly enhanced by either modification method. The co-precipitation reserves almost all of the Bronsted acid sites, while the impregnation causes a remarkable decrease of Bronsted acid sites. Reaction results demonstrate that the co-precipitation exhibits a significant advantage over impregnation that the higher conversion of n-butane and selectivity to isobutane are obtained on the catalyst prepared by co-precipitation. The increase of catalytic activity is ascribed to the accelerated activation rate of n-butane molecules by hydride subtraction on the Lewis acid sites at higher reaction temperature. Furthermore, the addition of La/Ni improves the selectivity to isobutane by inhibiting the bimolecular reaction. (C) 2016 Elsevier B.V. All rights reserved.
Keywords:Alumina-promoted sulfated zirconia;La;Ni;n-Butane isomerization;Impregnation;Co-precipitation