THE ROLE OF LI2CO3 MELTING IN THE ACTIVAT ION AND DEACTIVATION OF LI NB/MGO CATALYST FOR THE REACTION OF METHANE OXIDATIVE COUPLING/

The promotion effect of niobium on the Li/MgO catalyst for;methane oxi dative coupling has been investigated in some detail. Doping with Nh i nto the catalyst lowers the activation temperature for the coupling re action for some 50 degrees C. The lowered temperature falls into the r ange of Li2CO3 melting. Catalytic performance, DSC and TGA measurement reveal that the coupling reaction on Nh doped catalyst activates as t he temperature reaches the range of Li2CO3 partly melting, and the cat alyst starts to losing weight when the temperature runs over the metli ng point. Doping with Nh lowers and scatters the DSC peak of Li2CO3 me lting in the catalyst. The activation of the catalyst is very sensitiv e to the melting process, that there appears a shift in the activity - temperature curve around the melting point for some catalyst, and tha t there is a light off around the melting temperature for the coupling reaction when measured at CH4/O-2 = 5 and with no dilution. In the ag eing experiment with high methane oxygen concentration, when the tempe rature is a little bit lower than the melting point, there is no deact ivation observed for 65 hours, however, when the temperature is adjust ed to a little bit higher than the melting point, the activity reaches a very high level at the beginning but starts to deactivate quickly. When the catalyst is aged at constant temperature a little bit above t he melting point, the oscillation of the coupling reaction was observe d. These results indicate that both the activation and the deactivatio n of the Nh doped catalyst is related to the melting of the Li2CO3 in the catalyst.