Continuous monitoring the oxyfunctionalization of hexane by aqueous H2O2 over TS-1 related catalysts Original Research Article

The title reaction was studied over three TS-1 type catalysts at atmospheric pressure and at temperatures from 40 to 60 °C. By monitoring the consumption of H2O2 continuously we found that the selective oxidation of n-hexane to 2- and 3-hexanols and -hexanones proceeds usually faster than previous experiments suggest, but the reaction stops before reaching total hydrocarbon conversion despite ample H2O2 supply. One of our catalysts permitted >99% H2O2 utilization even in the absence of any homogenizing co-solvent. This material has an MFI structure but does not show significant UV absorption near 48,000 cm−1, which is a benchmark of the isomorphously substituted TS-1. Our other TS-1 catalyst, with a strong UV band near 48,000 cm−1, promoted the oxidation of n-hexane by aqueous H2O2 best in the presence of methanol. The hydroxyl content of catalysts and their Ti4+ coordination were compared by dispersive Raman and Fourier transform (FT) mid-infrared (MIR), near infrared (NIR), and UV spectroscopy. Spectra of hydrated and dehydrated samples were scanned from 900 to 52,000 cm−1 in a single DRIFT cell before and after in situ dehydration at ∼10−3 Pa pressure at temperatures from 25 to 400 °C. High-resolution FT-UV measurements indicated an array of charge transfer transitions for Ti4+ ions in every sample.