CHARACTERIZATION, ACTIVITY, AND ADSORPTION-DESORPTION BEHAVIOR OF ALKALI-PROMOTED MOLYBDATE CATALYSTS FOR THE OXIDATIVE COUPLING OF METHANE

MnMoO4 and alkali-promoted (Li, Na, or K) MnMoO4 catalysts have been e xamined for the methane oxidative coupling reaction. The catalysts wer e characterized by XRD, XPS, LRS, TPR, and TPD. The molybdate structur e appeared to remain intact, although the presence of the promoter ion s was found to change the TPR and TPD profiles. Increased selectivity to C2 hydrocarbons has been observed for similar conversion levels (Dr iscoll, Zhang, and Ozkan, in ''Catalytic Selective Oxidation'' (S. T. Oyama and J. W. Hightower, Eds.), Vol. 523, p. 340. ACS, Washington, D C, 1993) through the addition of the alkali-promoter ions, especially potassium. Further examination of the catalysts at equal residence tim es revealed an increased activity due to the addition of the alkali-pr omoter ions, with no change in activity or selectivity when excess car bon dioxide was added to the feed. While the TPD experiments provided clues as to the nature and function of surface oxygen, laser Raman spe ctroscopy studies provided evidence of the existence of carbonyl group s on the surface. (C) 1994 Academic Press, Inc.