Thermal conversion of methoxy species on dimethyl ether adsorbed CeO2

The behavior of methoxy species on dimethyl ether (DME) adsorbed CeO2 was investigated using temperature-programmed desorption (TPD) and infrared (IR) spectroscopy. TPD experiments showed that the thermal desorption peaks at 470-500 and 570 K are all DME from DME/CeO2 adsorbed at 300 K. These DME desorptions are attributed to the recombination of the surface methoxy species on CeO2. IR spectra of DME-adsorbed CeO2 showed two bands at 1158 and 1070 cm(-1) 300 K. These bands were assigned to the C-O stretching (nu(CO)) bands of surface methoxy species bound to one Ce ion (terminal-OCH3) and two Ce ions (bridged-OCH3), respectively. These bands decreased with increasing the temperature of CeO2. The increase of the temperature to 490 K led to the appearance of anew band at 1025 cm(-1) which was identified as nu(CO) of mu-OCH3 bound to more than three Ce ions; The TPD and IR results suggest that only the mu-OCH3 is decomposed into carbonate via a formate intermediate. The reactions of surface methoxy species on CeO2 are discussed.