Adsorption and reactions of CH3Cl on Mo2C based catalyst

The adsorption of CH3Cl on ZSM-5, Mo2C/ZSM-5 and Mo2C/SiO2 was investigated by temperature-programmed desorption (TPD) and Fourier transform infrared spectroscopy (FTIR). The formation of methoxy species was clearly identified on all the three catalysts. Three elementary steps were considered to explain the absorption bands observed in the IR spectra and to describe the reaction products found at higher temperatures: (i) the interaction of CH3Cl with the OH groups of ZSM-5, (ii) dissociation of CH3Cl yielding CH3 and (iii) the elimination of HCl from the adsorbed CH3Cl to give CH2 species. A new finding was the identification of the alkenyl carbocation formed on the Lewis acidic sites of ZSM-5. The decomposition of CH3Cl on ZSM-5 proceeded at 673 K with a high conversion yielding propylene, ethylene, butane, methane and benzene in decreasing selectivities. Deposition of Mo2C on ZSM only slightly modified the catalytic behavior of ZSM-5. Its promoter effect came into prominence on silica surface. (C) 2000 Published by Elsevier Science B.V.