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 cat alysts has been investigated. On catalysts with low La2O3 content (1 wt%) F TIR 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 progr essively until it completely disappears, while the band at 2122 cm(-1) incr eases and shifts to 2130 cm(-1). This band is assigned to CO adsorbed on ox idized Pt. This effect is observed on samples on which PtSn-La2O3 multiphas e coexists. The presence of Pt in an oxidized state is supported by XPS sin ce Pt2+ is present on the catalysts containing Pt/Sn and La2O3. On the othe r hand, XPS revealed the presence of Sn2+ and Sn degrees. For the n-heptane reaction the selectivity pattern of the PtSn/Al2O3-La catalysts shows tota l inhibition of the formation of benzene, high olefin content, and low n-C- 7 dehydrocyclization products. (C) 2001 Academic Press.