LI MGO SOL-GEL CATALYSTS

Li/MgO catalysts were synthesized through the sol-gel method (using ma gnesium diethoxide and lithium chloride) and by traditional impregnati on. FTIR results show that the sol-gel catalysts present higher hydrox ylation as compared with impregnated ones. The features of the IR spec tra are explained as the treatment temperature increases. In the prepa ration process of traditional impregnated catalysts much Mg(OH)2 is fo rmed which is later transformed into MgO by thermal treatment. BET are as are very similar for both types of catalysts. Theoretical semi-empi rical Extended Huckel (EH) and self-consistent field (SCF) calculation s were performed on Li/MgO model clusters to test the existence of [Li +O-] sites and oxygen vacancies. The EH calculations were done with Li concentrations varying from 2.66 to 15.9 wt. %. Results show a trend towards the formation of [Li+O-] centers when Li concentration increas es. This concentration effect is in agreement with the experimental re sults of methane activation. The SCF calculations using minimal and ex tended gaussian basis sets were performed on pure MgO and Li/MgO model clusters. These SCF results also show the creation of [Li+O-] sites w hich could explain the abstraction of hydrogen in the oxidative coupli ng of methane over Li/MgO catalysts.