Bulky macroporous titanium silicalite-1 free of extraframework titanium for phenol hydroxylation

A bulky composite material, CaCO₃@TS-1, was synthesized in a tetrapropylammonium bromide hydrothermal system by adding nanosized CaCO₃ particles of 60–80 nm to a titanium silicalite-1 (TS-1) synthesis gel. The macroporous TS-1 free of extraframework Ti was then obtained by the posttreatment of the CaCO₃@TS-1 in HCl solution to remove CaCO₃ and extraframework Ti simultaneously. This study demonstrates that this new synthesis route, the acidity posttreatment, can produce a bulky TS-1 with volume-controllable intracrystal macropores. The crystallization mechanism of the macroporous TS-1 was studied systematically. The addition of CaCO₃ accelerates the crystallization of silicon source, and leads to the similar crystallization rates of silicon and titanium sources. Therefore, the formation of extraframework Ti was inhibited, and more Ti ions were inserted into the TS-1 framework. The catalytic performance of macroporous TS-1 was evaluated in the hydroxylation of phenol. An outstanding catalytic activity was obtained due to their enhanced diffusion property and reduced extraframework Ti.