Abstract
A series of microporous titania–silica mixed oxides werecharacterized and tested as catalysts for the liquid-phaseepoxidation of 1-hexene witht-butyl hydroperoxide. Results from29Si MAS NMR spectroscopy verified results from earliercharacterization studies that indicated cohydrolysis of alkoxideprecursors produced well-mixed oxide samples. The catalyticactivity of the samples for hexene epoxidation at 353 Kincreased withincreasing silica content. Since the fraction of tetrahedral Tiatoms in the samples also increased with silica content, theactive site for the reaction is proposed to be a tetrahedrallycoordinated Ti atom in a silica matrix. Polar solvents likewater, acetone, and methanol inhibited the epoxidation reaction.To investigate the effect of pore size on activity, mesoporousTi–Si mixed oxides analogous to MCM-41 were synthesized. Themesoporous samples were the most active and selective catalystsfor epoxidation with TBHP, presumably due to the ease of accessof the reactants to the active Ti sites. Results from EXAFS andUV reflectance spectroscopy indicated that Ti atoms in themesoporous mixed oxides are tetrahedrally coordinated to oxygenatoms with the same Ti–O bond distance as TS-1. However, theactivities of our mesoporous samples are orders of magnitudelower than that of TS-1 for hexene epoxidation with aqueoushydrogen peroxide. Lower hydrophobicity of a silica mesopore(2–4 nm) compared to a TS-1 micropore (0.6 nm) may account forthe difference in activity observed in reactions with aqueoushydrogen peroxide.
Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
