Surface Cristobalite Formation by Mild Hydrothermal Treatment of Silica Gel and Its Effect on the Deposition of Tris(aIlyl)rhodium and Subsequent Reactivity of (silica)Rh(allyl)₂

Titrimetric analysis of surface silanol sites with methyllithium measures total surface -OH group content. This correlates with simple drying but does not predict organorhodium complex deposition loadings onto the oxide. It is suggested that methyllithium does not discriminate among chemically different types of silanol sites as does tris(allyl)rhodium. Furthermore, there is no correlation between simple silica gel drying procedures and the subsequent reactivity of the supported organometallic. A sequence of mild hydrothermal treatment (hydration), followed by drying of the silica, enhanced organorhodium complex deposition yields and enabled reproducibility of supported complex reactivity. Transmission and photoacoustic FTIR analysis of silicas treated by hydration-drying showed new absorptions in the isolated -OH and Si-O-Si ring deformation regions of the spectra, demonstrating surface cristobalite formation. No change in silica surface area was detected for this process.