Add time:09/30/2019         Source:infona.pl

A series of sulfated silica MCM-41 samples denoted as SM and ASM were prepared by calcination at different temperatures using H 2 SO 4 and (NH 4 ) 2 SO 4 solution as the promoter, respectively. The mesostructure, sulfation process, and surface acidity of the two samples were investigated by N 2 adsorption-desorption, temperature-programmed desorption of adsorbed NH 3 (NH 3 -TPD), thermogravimetric analysis (TG-DTG), elemental analysis, and Fourier transform infrared (FT-IR) spectroscopy. The activity of the samples for the traditional liquid acid-catalyzed cyclization reaction of PSEUDOIONONE (cas 141-10-6) to ionones was investigated. For the SM and ASM samples calcined at 450°C (denoted as SM-450 and ASM-450, respectively), SO 4 2- was successfully chelated onto the silica surface in bidentate complex forms, and no free H 2 SO 4 molecules existed as the original promoter or intermediate of thermal decomposition inside the mesopores. The in situ pyridine adsorption FT-IR and NH3-TPD measurements revealed that ASM-450 contained both Brønsted and Lewis acid sites of weak strength. The catalytic performance of SM-450 and ASM-450 was comparable with that of the commercial acid resin Amberlyst-15, and the chelating structure of SO 4 2- /SiO 2 , which was generally considered to be inactive, was responsible for the high activity. ASM-450 showed better catalytic performance compared with Amberlyst-15 at relatively low temperature, and it could be reused 5 times with good activity.

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