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Crystallization of Ti-Rich *BEA Zeolites by the Combined Strategy of Using Ti–Si Mixed Oxide Composites and Intentional Aluminum Addition/Post-Synthesis Dealumination
journal contribution
posted on 2018-03-23, 18:04 authored by Hirofumi Horikawa, Takayuki Iida, Ryota Osuga, Koji Ohara, Junko N. Kondo, Toru WakiharaTitanosilicate
zeolites are well-known catalysts for selective
oxidation using hydrogen peroxide, an environmentally friendly oxidant.
To effectively synthesize these materials with high Ti contents, we
have focused on using a Ti–Si mixed oxide composite as the
ingredient along with intentional addition of an aluminum source to
promote crystallization. Ti-beta, a *BEA-type zeolite containing titanium
at the framework sites, was chosen as a model zeolite. First, (Ti,
Al)-beta, a *BEA-type zeolite containing both Ti and Al, was prepared;
the occluded aluminum inside the product was subsequently removed
by an acid treatment. This treatment not only lead to the reduction
of the aluminum content to trace levels but also improved the states
of the titanium species to the desired tetrahedral coordination state.
Thus, Ti-beta zeolites with little extra-framework Ti were successfully
obtained with molar compositions up to Ti/(Ti + Si) = 4.0 mol %. As
a titanosilicate zeolite catalyst, high functionality was demonstrated
based on the oxidation of cyclooctene, confirming the positive impact
of having high titanium content with low aluminum content. Finally,
investigation of the intermediates during the crystallization process
was performed to understand the behavior of titanium species throughout
the crystallization and to propose the critical factors for achieving
efficient Ti introduction.