Synthesis of CHA-type titanosilicate zeolites using titanium oxide as Ti source and evaluation of their physicochemical properties

Abstract

To improve the physicochemical properties of CHA-type zeolites, we synthesized a CHA-type titanosilicate zeolite (Ti-CHA) with titanium instead of aluminum incorporated into its framework. Ti-CHA zeolites with various Si/Ti ratios were directly prepared by a 24-h hydrothermal reactions with the use of colloidal silica and titanium oxide as Si and Ti sources, respectively. A peak, assignable to isolated tetrahedrally coordinated Ti species, was clearly observed at ca. 220 nm in the UV–vis spectra of the Ti-CHA zeolite, confirming that titanium was incorporated into the zeolite framework. The effects of titanium content in the CHA zeolite on the thermal and acid stabilities were investigated. No changes were observed in the crystallinity, BET surface area, and micropore volume of a Ti-CHA zeolite with a Si/Ti ratio of 347, even after thermal treatment at 1150 °C. Furthermore, no changes were observed in the crystallinity of Ti-CHA zeolites with Si/Ti ratios of 45–347, after treatment with aqueous hydrochloric acid at 75 °C for 5 days. The amount of water adsorbed by the Ti-CHA zeolite with a Si/Ti ratio of 347 was lower than those of high-silica CHA-type zeolite with Si/Al = 10 (Al-CHA zeolite) and pure-silica CHA-type zeolite (Si-CHA zeolite).