1-hexene isomerization over sulfated mesoporous Ta oxide: The effects of active site and confinement

The isomerization of 1-hexene at 343 K was conducted over, a series of sulfated mesoporous Ta oxides with pore sizes ranging from 12 to 30 A. The results were compared to the popular industrial catalysis HY-zeolite, H-ZSMS, and Ambertyst 15. The conversion of 1-hexane to transcist-2-isomers can reach 95.89% in 4 h, which is roughly 2 times faster than Ambertyst 15 and 20 times faster than HY-zeolite and H-ZSM5. GC analysis confirmed that trans- and cis-2-hexane isomers formed through a double bond shift process as the only two principal products. The molar ratio of translcis-2-hexene isomers varies with pore size, clearly showing confinement effects in this process. The selectivity or our best material toward the trans-isomer is at least 3 times greater than that of either zeolite or Amberyst 15. The best catalytic results in this study were achieved when using C-12 H2SO4 mesoporous Ta oxide, which possesses apK(a) of -8.2 and 19.8 mmol/g acid sites. The X-ray diffraction pattern showed complete retention of the mesostructure throughout catalysis as evidenced by a single brand reflection. Pyridine adsorption and infrared spectroscopy (IR) suggest that both Bronsted sites (similar to 1538 cm(-1)) and Lewis sites (similar to 1443 cm(-1)) coexist on the surface of these materials. The large amount of Bronsted acid sites, high BET surface areas, high acid strength Ho, and superior diffusion properties of C12H2SO4 mesoporous To oxide are probably responsible for its extremely high catalytic activity and selectivity.