Synergistic catalysis effect in pentanol conversion into di-n-pentyl ether on ZSM-5 supported titania catalysts synthesized by sol–gel

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 1123 cm−1) results besides surface texturing data that showed lower surface areas (524–480 m2 g−1) and pore volumes (0.4955–0.4530 cm3 g−1) as compared to the parent (587 m2 g−1 and 0.5642 cm3 g−1). A distortion of tetrahedral Ti species was 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.