Structural characterization of Cr/MCM-41 and polymerization of ethylene within its nanoscale channels

The important characteristics of MCM - 41 such as large BET surface area, high porosity, large - diameter channel apertures, controllable and narrowly distributed pore sizes make this material a very promising candidate for catalyst or catalyst support. In this work, the use of MCM - 41 as a support for chromium,which is phillips' active site for olefin polymerization,and the potential application of Cr modified MCM - 41 in ethylene polymerization were investigated. The Cr/MCM - 41 was characterized by XRD, Nz adsorption, FT - IR, Raman and MMR spectroscopy. The XRD and Nz adsorption results showed that G-/MCM - 41 catalysts still possessed long - ordered structures, large surface areas and uniform pore diameters. Chromium species was well dispersed on the surface of MCM - 41 until the chromium loading reached 7%. FT - IR and Raman spectra indicated that the well dispersed Cr species was present as isolated at low Cr loading, while as both isolated and polymerized at high loading. NMR spectra suggested Cr species was dispersed on the surface of MCM - 41 probably by interacting with the hydroxyls. PE with a certain conformation can be formed within the nanoscale one - dimensional channels of MCM - 41 without destroying the pore structure,which seemed to indicate an promising application of MCM - 41 in nano - composites. The comparison between Cr/MCM - 41 and Cr/SiO2 has also been made.