关键词: 氧化, 镁, 催化剂, 铌, 甲烷, 锂, 熔点, 偶联, 碳酸锂

The promotion effect of niobium on the Li/MgO catalyst for methane oxidative coupling has been investigated in some detail. Doping with Nb into the catalyst lowers the activation temperature for the coupling reaction for some 50℃. The lowered temperature falls into the range of Li2CO3 melting. Catalytic performance, DSC and TGA measurement reveal that the coupling reaction on Yb doped catalyst activates as the temperature reaches the range of Li2CO3 partly melting, and the catalyst starts to losing weight when the temperature runs over the metling point. Doping with Nb lowers and scatters the DSC peak of Li2CO3 melting in the catalyst. The activation of the catalyst is very sensitive to the melting process, that there appears a shift in the activity-temperature curve around the melting point for some catalyst, and that there is a light off around the melting temperature for the coupling reaction when measured at CH4/O2=5 and with no dilution. In the ageing experiment with high methane oxygen concentration, when the temperature is a little bit lower than the melting point, there is no deactivation observed for 65 hours, however, when the temperature is adjusted 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 the melting point, the oscillation of the coupling reaction was observed. These results indicate that both the activation and the deactivation of the Nb doped catalyst is related to the melting of the Li2CO3 in the catalyst.

Key words: OXIDATION, MAGNESIUM, CATALYST, NIOBIUM, METHANE, LITHIUM, MELTING POINT, COUPLED, LITHIUM CARBONATE