The reaction of propylene to propylene-oxide on CeO2: An FTIR spectroscopy and temperature programmed desorption study.

Abstract

The potential of CeO2 as an epoxidation catalyst is studied for the reaction of propylene with hydrogen peroxide (H2O2) by Fourier transform infrared (FTIR) spectroscopy and temperature programmed desorption (TPD). Adsorption and decomposition of H2O2 and propylene oxide (PO) are also explored to determine their surface chemistry and thermal stability. Hydrogen peroxide adsorbed dissociatively on CeO2 forming adsorbed peroxo (O-O) species, as observed through vibrational features at 890 cm-1 and (830-855) cm-1 (FTIR). The signal at 890 cm-1 disappeared when a pulse of propylene was passed through the catalyst, and at the same time, adsorbed PO was observed (a sharp IR mode at 827 cm-1; ring deformation). The reaction between gas phase propylene and adsorbed peroxide species suggested the Eley-Rideal type mechanism. The absence of a ring opening reaction of PO at room temperature may indicate that CeO2 can be a suitable oxide for epoxidation of hydrocarbons. PO started to decompose above 323 K, as observed from FTIR and TPD results. TPD spectra of PO show its desorption at 365 K, with a small fraction decomposing into acetaldehyde and formaldehyde due to partial decomposition, while CO2 and CO are released at higher temperatures. Adsorbed acetate, formate, and carbonate species, formed due to further reactions of aldehydes, are observed during the thermal reaction (FTIR).