The Inhibiting Effect of Lanthanum on the Formation of Benzene over PtSn/Al2O3 Reforming Catalysts

The effect of La2O3 on the catalytic properties of PtSn/Al2O3 reforming catalysts has been investigated. On catalysts with low La2O3 content (1 wt%) FTIR CO adsorption spectra show two absorption bands at 2070 and 2122 cm−1. At higher La2O3 content (20 wt%) the band at 2070 cm−1 diminishes progressively until it completely disappears, while the band at 2122 cm−1 increases and shifts to 2130 cm−1. This band is assigned to CO adsorbed on oxidized Pt. This effect is observed on samples on which PtSn–La2O3 multiphase coexists. The presence of Pt in an oxidized state is supported by XPS since Pt2+ is present on the catalysts containing Pt/Sn and La2O3. On the other hand, XPS revealed the presence of Sn2+ and Sn°. For the n-heptane reaction the selectivity pattern of the PtSn/Al2O3–La catalysts shows total inhibition of the formation of benzene, high olefin content, and low n-C7 dehydrocyclization products.