Spectroscopic Study of H2and CO Adsorption on Platinum-Promoted Sulfated Zirconia Catalysts

H 2 adsorption over two Pt/SO 4 2- −ZrO 2 (Pt/SZ) samples pretreated under different conditions (one is catalytically active and the other is inactive in n -butane isomerization) was investigated by in-situ Fourier transform infrared (FTIR) spectroscopy and temperature-programmed desorption (TPD). It was found that the formation of H 2 O was the crucial difference between the active and inactive Pt/SZ samples upon H 2 adsorption at 523 K, with isolated zirconium OH groups forming on both samples. Under the same conditions, neither H 2 O nor zirconium OH groups formed on SO 4 2- −ZrO 2 (SZ), and only a small amount of OH groups formed on Pt/ZrO 2 . CO adsorption results reveal the presence of both Brφnsted and Lewis acid sites on the surface of Pt/SZ, as well as the transformation of Lewis acid sites to Brφnsted acid sites upon H 2 adsorption at 523 K. These results present direct evidence of H 2 spillover from Pt to the sulfated zirconia surface. The formation mechanism of H 2 O and OH groups is discussed, and it is suggested that the active oxygen species, which should be associated with the intermediate sulfate species on the active Pt/SZ surface, plays an essential role as active sites on Pt/SZ in n -butane isomerization.