Spectroscopic study of H2 and CO adsorption on platinum-promoted sulfated zirconia catalysts

H-2 adsorption over two Pt/SO42--ZrO2 (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 H2O 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 H2O nor zirconium OH groups formed on SO42--ZrO2 (SZ), and only a small amount of OH groups formed on Pt/ZrO2. CO adsorption results reveal the presence of both Bronsted and Lewis acid sites on the surface of Pt/SZ, as well as the transformation of Lewis acid sites to Bronsted 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 H2O 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.