Post-synthesis, characterization and catalytic properties of fluorine-planted MWW-type titanosilicate

Abstract

F-Ti-MWW was post-synthesized by implanting fluorine species into a Ti-MWW framework through an acid treatment process in the presence of ammonium fluoride. The effects of NH4F addition amount, acid treatment temperature and precursor Ti content were investigated on the incorporation of F species, the zeolite structure and the coordination sites of Ti. Fluorine-implanting improved the surface hydrophobicity of the zeolite and altered the electropositivity nearby the tetrahedral Ti sites through forming the SiO3/2F and SiO4/2F(-) units. The negative effect of SiO4/2F(-) units in F-Ti-MWW was eliminated selectively by convenient anion-exchange with various alkali chlorides. F-Ti-MWW containing the SiO3/2F units possessed better catalytic activity and reusability, and a longer catalyst lifetime than conventional Ti-MWW.

Insights into the key to highly selective synthesis of oxime via ammoximation over titanosilicates

“…The precursor was acid-treated with 2 M HNO 3 at a solid-to-liquid weight ratio of 1: (30 or 50) to remove the extra-framework Ti species and part of framework boron under the reflux conditions. F-Ti-MWW was prepared according to a procedure reported recently [28]: the Ti-MWW precursor (Si/Ti = 25) was treated in 2 M HNO 3 solution by addition of NH 4 F (Si/F = 26) at a solid-to-liquid ratio of 1 g to 30 mL at 377 K for 5 h. All acid treatment samples were further calcined in air at 823 K for 8 h to obtain Ti-MWW with different Si/Ti molar ratios and F-Ti-MMW catalysts (Si/Ti = 29).…”

A one-step rapid synthesis of TS-1 zeolites with highly catalytically active mononuclear TiO6species

“…[18][19][20][21][22] To date, several strategies have been proposed to modify the Ti active centers in Ti-containing zeolites. [23][24][25][26][27] For instance, Fang et al reported a strategy to increase the electropositivity of the Ti active sites in the Ti-MWW zeolite by implanting the F species on the neighboring framework Si, and thus the catalytic property of such Ti species got enhanced. 23 However, the simultaneously formed harmful F species, which lowered the catalytic property of the Ti active sites, must be eliminated aerward.…”

“…[23][24][25][26][27] For instance, Fang et al reported a strategy to increase the electropositivity of the Ti active sites in the Ti-MWW zeolite by implanting the F species on the neighboring framework Si, and thus the catalytic property of such Ti species got enhanced. 23 However, the simultaneously formed harmful F species, which lowered the catalytic property of the Ti active sites, must be eliminated aerward. To overcome the complex synthetic procedure, in some other cases, the Ti active sites were directly modied via the post-treatment approach.…”

Structured binder-free MWW-type titanosilicate with Si-rich shell for selective and durable propylene epoxidation

“…It was commonly believed that the zeolite materials that contained sufficient densities of the silanols like isolated ≡Si−OH, gemini-type =Si−(OH)2 or hydroxyl nests (Si−OH)4 tend to adsorb H2O molecules via the stable hydrogen-bond interactions [41][42][43]. In the hydroxyl stretching region of IR spectra, the bands at 3745, 3720, 3676 and 3510 cm -1 were attributed to the external isolated Si−OH, internal Si−OH, Ti−OH and (Si−OH)4, respectively [44]. As shown in Fig.…”