Sulfated zirconia catalysts promoted with Fe and Mn: Mn effect in the Fe dispersion

Abstract

n-Butane conversion was studied over Fe- and Mn-promoted sulfated zirconia by pulse reaction over the temperature range of 423–503 K to explore the role of Mn in the catalytic activity of Fe-promoted sulfated zirconia. On a sample containing 2 wt.% Fe, the n-butane isomerization activity was found to decrease with decreasing Fe/Mn molar ratio beyond 0.65 wt.% Mn. Concomitantly, XPS showed that the surface Fe/Zr intensity ratio increases with the Mn content until it reaches a maximum at 0.65 wt.% Mn, and then decreases. This behavior reflects a higher Fe dispersion at relatively low Mn content. Thus, low concentrations of Mn disperse the iron on the surface. Temperature programmed reduction data indicate that more sulfate species are accessible to reduction when metal promoters are present over sulfated zirconia. However, increasing Mn amount decreases the fraction of sulfate being reducible.