Oxidative coupling of methane over alkaline earth oxides deposited on commercial support precoated with rare earth oxides

A number of supported catalysts, prepared by depositing alkaline earth (viz. Mg, Ca, Sr and Ba) oxides on a commercial support (SA-5205) precoated with various rare earth (viz. La, Ce, Nd, Sm, Gd, Er and Yb) oxides have been evaluated for their surface properties and activity/selectivity in oxidative coupling of methane (OCM) at low contact time (GHSV = 1.02 x 10(5) cm(3) g(-1) h(-1)). The catalysts have been characterized for their basicity and acidity distributions by temperature programmed desorption (TPD) Of CO2 and ammonia from 50 degrees C to 950 degrees C, respectively, and for their oxygen chemisorption sites by TPD of O-2. The OCM activity of the catalysts has been correlated with their basic sites measured in terms of the CO2 desorbed between 500 degrees C and 950 degrees C. The catalysts with La2O3 and/or Nd2O3, showing good OCM activity, have been compared for their performance in the OCM process at different temperatures (750 degrees C-850 degrees C), and CH4/O-2 ratios (4.0-20.0) in the feed. At 850 degrees C, the catalyst with SrO deposited on the support precoated with mixed La2O3-Nd2O3 shows best performance in the OCM process. (C) 1999 Elsevier Science Ltd. All rights reserved.