Isomerization of n-butane over Fe,Mn-promoted sulfated zirconia: catalytic activity and surface features of the catalyst

The catalytic properties of Fe,Mn-promoted sulfated zirconia catalysts have been tested as a function of: (i) the temperature of the preliminary calcination step; (ii) the conditions of the catalyst activation step; (iii) the temperature of the catalytic reaction. It was observed that the promotion effect is mainly ascribable to the Fe component, and requires: (i) a preliminary calcination at Tcalc>850 K, most likely to liberate from sulfates as much as possible of the surface Fe component; (ii) an activation cycle (at Tact≈ 700 K) in strictly oxidizing conditions, in order to have as much as possible of the surface FeIII component in a reducible form; (iii) reaction temperatures close to ambient temperature, in order to prevent the predominance of poisoning reactions and to avoid an extensive reduction of the Fe component. When the Fe component becomes reduced, the catalytic promotion effect is lost, and the reduced Fen+ component (n>3) can be easily revealed by the ambient temperature adsorption of CO, which yields a typical IR band centered at ~2170 cm-1.