The synthesis of TiZSM-5 (TiZ) catalysts using acid catalyzed sol–gel method via different molar ratios of
tetra-isopropyl orthotitanate [Ti(O-i-Pr)4] was thoroughly characterized by inductively coupled plasma
optical emission (ICP-OE), X-ray diffraction (XRD), particle size analyzer, N2 adsorption, pyridine-FTIR
and ultra-violet visible (UV–vis) spectroscopy. Liquid phase dehydration of 1-pentanol to di-n-pentyl
ether (DNPE) was tested for the catalysts. Characterization of TiZSM-5 catalysts clearly shows that
at low loadings (up to 5 wt%) titanium atoms were on the inner surface of zeolite layers mainly in
tetrahedral environment as conceived from UV–vis (248–260 nm) and IR (960 and 1123cm−1) results
besides surface texturing data that showed lower surface areas (524–480m2 g−1) and pore volumes
(0.4955–0.4530cm3 g−1) as compared to the parent (587m2 g−1 and 0.5642cm3 g−1). A distortion of
tetrahedral Ti specieswas perceived at high-titania loadings (≥10 wt%) evidencing its existence on zeolite
surfaces as a distinctive anatase phase. The catalytic dehydration of 1-pentanol over 5, 10 and 15 wt% TiZ
catalysts achieved 70% conversion and 10TiZ showed the highest selectivity (60%) to DNPE. This was due
to enhancing Brönsted acid sites, retaining crystallinity, decreased particles size and to the relatively large
BET surface area. The effect of temperature (298–523 K), time (4–16 h), titania loadings (2.5–15 wt%) as
well as solvent engagement on the selectivity to DNPE was thoroughly investigated. The nano-sized TiO2
crystals in/on 10TiZ surfaces and zeolite pore volume seem to provide excellent possibilities for diffusion
of reactants and products, which of significant importance in heterogeneous catalysis.
© 2008 Elsevier B.V. All |
