Tuning porosity of Ti-MCM-41: implication for shape selective catalysis.

This paper describes a method to regulate porosity of Ti-containing mesoporous molecular sieves (Ti-MCM-41) by employing swelling agents that are hydrophobic in nature, such as dodecylamine, n-heptane, and sym-trimethylbenzene (TMB). Physicochemical properties of the samples were investigated using XRD, FT-IR, IR spectra of pyridine absorption, UV-vis, TEM, and N(2) adsorption-desorption techniques. Addition of favorable swelling agents leads to an increase in pore size accompanied by retaining the mesostructure with a certain decrease of structure ordering. Swelling agents also have significant impact on the integration of Ti into the silica framework, which further affect the formation of Lewis acid sites. N-heptane is the most favorable agent for pore expansion of Ti-MCM-41. The material with n-heptane/CTAB ratio of 1 exhibits the largest pore size of 48.3 Ǻ, and mesopore volume of 1.266 cm(3)/g and narrow pore-size distribution. We also demonstrated that shape-selective transesterification catalytic activity of Ti-MCM-41 was greatly enhanced because of pore expansion.