A COMPARATIVE-STUDY OF THE OXIDES OF LANTHANUM, CERIUM, PRASEODYMIUM, AND SAMARIUM AS CATALYSTS FOR THE OXIDATIVE DEHYDROGENATION OF METHANE IN THE PRESENCE AND ABSENCE OF CARBON-TETRACHLORIDE

The catalytic oxidative coupling of methane to ethane and ethene has been investigated on the rare earth oxides. i.e., La2O3, CeO2, Pr6O11, and Sm2O3. Addition of a small amount of tetrachloromethane (TCM) to the reactant stream improves the catalytic activity of these oxides. In particular, the praseodymium catalyst yields high selectivity to the C2 compounds comparable to La2O3 or Sm2O3 when TCM is present in the feedstream. The X-ray diffraction patterns for these catalysts after the reaction with TCMshow the presence of the oxychlorides in the catalysts except forthe cerium catalyst, for which the selectivity to C2 compounds is very low even in the presence of TCM. The oxychlorides can be generated on La2O3, Sm2O3, or Pr6O11 by preheating under a stream including TCM. The product distribution of the reaction with these catalysts in the absence of TCM is similar to that with the oxides in the presence of TCM, while Pr6O11 pretreated with TCM is unstable with no TCM in the feedstream. It appears that the improvement of the activity of the rare earth catalysts with TCM in the feedstream is primarily due to the formation of the oxychlorides during the reaction. © 1993 Academic Press, Inc.