Cr(II) and Cr(III) Ions Grafted at Internal Nests of a Pentasilic Zeolite (Silicalite) - Characterization and Formation of Polycarbonylic, Polynitrosylic, and Mixed Species by Interaction with CO and NO

Nests of OH groups localized at defective positions inside the silicalite framework can react with chromic acid to give grafted chromate (and/or dichromate) species. Successive reduction in CO yields mainly Cr(II) species anchored to the framework, which upon CO and/or NO dosage form well-defined polycarbonylic, polynitrosylic, and mixed CO/NO complexes fully characterized by IR spectroscopy. The grafted Cr(II), and possibly Cr(III), ions are efficient centres for ethylene polymerization. Time-resolved IR spectra show that the polymeric chains formed inside the silicalite channels are short and have spectroscopic features different from those of the longer chains formed on the external surface.