Pt-H2SO4/Zr-montmorillonite: An efficient catalyst for the polymerization of octamethylcy-clotetrasiloxane, polymethylhydrosiloxane and hexamethyldisiloxane to low-hydro silicone oil

Abstract The liquid phase ring-opening of octamethylcy-clotetrasiloxane (D 4 ) was investigated over Pt-H 2 SO 4 /Zr-montmorillonite catalyst. Montmorillonite (Mt), Zr-Mt, H 2 SO 4 /Mt, H 2 SO 4 /Zr-Mt and Pt-H 2 SO 4 /Zr-Mt were also detected for evaluation. The catalysts were characterized by X-ray fluorescence, X-ray diffraction, nitrogen adsorption–desorption, NH 3 -TPD and pyridine-FTIR measurements. In comparison to activate clay which is used in the industry of catalyst, Zr-Mt catalyst displayed stronger acidity and more excellent catalytic activity in the polymerization of D 4 , polymethylhydrosiloxane (D 4 H ) and hexamethyldisiloxane (MM) to low-hydro silicone oil. Relative to Zr-Mt, the acidity of H 2 SO 4 /Zr-Mt was noticeably improved and the catalyst exhibited a higher capability of ring-opening of D 4 conversion and yield of low-hydro silicone oil. To enhance the stability of H 2 SO 4 /Zr-Mt catalyst, a small amount of metals (Pt) was doped. The nitrogen adsorption–desorption results indicated that pore textural parameters of the Pt-H 2 SO 4 /Zr-Mt had not changed with larger specific surface area. Compared with H 2 SO 4 /Zr-Mt, the total acidity of Pt-H 2 SO 4 -Zr/Mt catalyst retained, but the content of the Bronsted acid increased and the content of the Lewis acid decreased. The Pt-H 2 SO 4 -Zr/Mt catalyst displayed higher catalyst reproducibility. After 40 h reaction of polymerization, the yield of low-hydro silicone oil decreased from 93% to 42% over H 2 SO 4 /Zr-Mt catalyst, while the yield of low-hydro silicone oil reduced from 93% to 78% over Pt-H 2 SO 4 /Zr-Mt catalyst. A sharp decrease in catalytic activity after 35 h of Pt-H 2 SO 4 /Zr-Mt catalyst was detected. Furthermore, Pt-H 2 SO 4 /Zr-Mt was completely regenerated under appropriate condition and appeared good repeatability in the D 4 , D 4 H and MM to low-hydro silicone oil.