WHY ARE SOME TITANIUM SILICALITE-1 SAMPLES ACTIVE AND OTHERS NOT

Titanium silicalite-1 samples of different particle size are synthesized. X-ray diffraction (XRD), infrared (IR), Si-29 magic angle spinning nuclear magnetic resonance (MAS NMR), diffuse reflectance electron absorption spectrometry (DREAS), thermogravimetric analysis (TGA), pore volume and particle size measurements are used to characterize these samples. In the hydroxylation of phenol with hydrogen peroxide large differences in activity are found between different TS-1 samples. Using XRD, IR, Si-29 MAS NMR, and DREAS measurements it is impossible to differentiate between active and less active samples. Particle size determination (directly by scanning electron microscopy (SEM), Coulter Counter, and Malvern and indirectly by TGA and adsorption measurements) however can explain these differences. Smaller particles are more active than larger particles. From calculations of the Weisz modulus it can be concluded that large zeolite particle are not fully utilized because of pore diffusion limitations. The product distribution is also influenced by particle size.