Ethanol-assistant synthesis of TS-1 containing no extra-framework Ti species

Abstract

Titanium silicate-1 (TS-1) was synthesized via three different procedures, respectively, using tetraethylorthosilicate (TEOS) and tetrabutyl orthotitanate (TBOT) as Si and Ti sources and tetrapropylammonium hydroxide (TPAOH) as template. In the procedures A and B, ethanol and isopropanol were respectively employed as the solvents of TBOT and were remained all through the hydrothermal crystallization of TS-1. In the procedure C, isopropanol was also employed as the solvent of TBOT but was evaporated before the crystallization step. The TS-1 specimens synthesized via the three procedures were characterized by means of XRD, FT-IR, DRS UV–vis, SEM, N 2-physisorption and NH 3-TPD. It was shown that, the contents of framework Ti species in the TS-1 basing on the procedures A and C were comparable, being both larger than that basing on the procedure B. Extra-framework Ti, anatase, was absent in the TS-1 basing on the procedure A but present in the TS-1 basing on the procedures B and C, with its content being larger for the procedure B than for the procedure C. The extra-framework Ti might disperse highly both on the surfaces and in the micropores of TS-1. The framework Ti contributed the weak acid sites and the extra-framework Ti the strong acid sites of TS-1. The catalytic performance for the ammoximation of cyclohexanone over the TS-1 synthesized via various procedures was evaluated and the yield of cyclohexanone–oxime was found to follow an order procedure A > procedure C > procedure B. It was concluded that the TS-1 with a large content of framework Ti but without anatase, exhibiting high catalytic performance, could be effectively synthesized by the employment of ethanol.