Effects of calcination temperature and water-washing treatment on n-hexane hydroisomerization behavior of Pt-promoted sulfated zirconia based catalysts

摘要

Synthesis of Pt-promoted sulfated zirconia catalyst Pt/SO4~(2-)/ZrO2 (designated as PSZ), Pt/SO4~(2-)/ZrO2-Al2O3 (designated as PSZA), and Pt/SO4~(2-)/ZrO2-Al2O3-Y2O3 (designated as PSZAY) was reported. These catalysts were characterized by N2 adsorption-desorption, thermal gravimetric (TG) analysis, NH3-temperature programmed desorption (NH3-TPD), and H2-temperature programmed reduction (H2-TPR) techniques. Effects of calcination temperature of the catalysts on the n-hexane hydroisomerization behavior were investigated in details. The experiment results revealed that the addition of Al and Y or Al promoter alone could improve the thermal stability of the catalysts. PSZA and PSZAY exhibited higher isomerization activity than unmodified PSZ as the calcination temperature of sulfated Zr(OH)4 was relatively high, for example, between 650 °C and 750 °C For the first time, it was found that water-washing treatment of PSZA and PSZAY at different preparation stages had considerably different impacts on their catalytic activity. Water-washing after calcination of the sulfated Zr(OH)4, the catalytic activity of PSZA and PSZAY was high, as indicated by approximately 80% of n-hexane conversion. However, water-washing before calcination of sulfated Zr(OH)4 led to a significant decrease in the catalytic activity of PSZA and PSZAY, that is, the n-hexane conversion diminished to around 35%. It was proposed that the presence of excessive sulfur species over sample was favorable for keeping the active sulfur species in the catalyst surface.