The role of Cl- in a Li~+-ZnO-Cl- catalyst on the oxidative coupling of methane and the oxidative dehydrogenation of ethane

摘要

The effect of Cl~- ion addition to a Li~+-ZnO catalyst has been studied with respect to the oxidative coupling of CH4 and the oxidative dehydrogenation (OXD) of C2H6. Increasing the Cl/Li ratio from 0.65 to 0.90 had relatively little effect on the CH4 conversion, whereas the C2H4/C2H6 ratio was enhanced significantly as a result of an increase in the OXD reaction rate. Conversely, loss of Cl- from the catalyst during the reaction had a much more deleterious effect on ethane OXD activity than on methane coupling activity. Addition of Cl- ions at a Cl/Li ratio of 0.9 caused a decrease both in the number of basic sites and in the basic strength of these sites, as determined by temperature-programmed desorption of CO2. The similarities between the results obtained over Li+-ZnO-Cl- catalysts and those previously reported for Li+-MgO-Cl- catalysts confirm that basicity of the host oxide plays only a minor role in determining the properties of these chlorided catalysts.