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 Broensted 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