Study of n-Butane Isomerization on Acid Catalysts Niobium and Lanthanum Promoted Tungstated Zirconia: n-Butane Isomerization Activity

Abstract

The requirement for environmentally friendly catalysts for the isomerization of alkanes has prompted research on the tungstate-zirconia (WZ) system. The present work examines the activity and selectivity of lanthanum (La) promoted tungstate-zirconia (LWZ) and niobium (Nb) promoted tungstate-zirconia (NWZ) catalysts. In this study, 1 % La promoted WZ (1 % LWZ) and 1 % Nb promoted WZ (1 % NWZ) catalysts were investigated in isomerization of n-butane in the presence of hydrogen. The studied catalysts were characterized by different methods: nitrogen physisorption, temperature programmed desorption of NH3, thermogravimetric analysis, and X-ray diffraction. The catalytic activity and selectivity were significantly improved by the addition of 1 % Nb. The redox process in the Nb-containing catalyst (1 % NWZ) played a central role by providing the highest acidic sites (283.53 µmol g–1) with appropriate activation energies for the skeletal rearrangement of the reactant (n-butane). Furthermore, this study highlights the determining role of the transfer process of adsorbed species from ZrO2 to W as well as to the Nb environment. The conversion of n-butane (27.34 %) and the selectivity to i-butane (92.34 %) for NWZ were significantly higher than WZ and LWZ catalysts. The experimental results revealed that Nb was a more effective promoter than La.

Keywords

• tungstated zirconia
• n-butane isomerization
• niobium
• lanthanum
• acidity